Hurricane Katrina

Heatwave Summer 2018

map of ukMore links and images will be added to this page as they are identified.

A comparison between 1976 and 2018 from the BBC.

This fairly lengthy discussion from the Met Office has some good maps and statistics.

Wildfires on Saddleworth Moor and Glenshane Pass, 27.6.18. Image reproduced with thanks from University of Dundee satellite receiving station.

And the corresponding Met Office chart, showing the High pressure/ polar continental conditions which dominated during the heatwave.

Case Study – The Great Smog

The Great Smog of 1952

A fog so thick and polluted it left thousands dead wreaked havoc on London in 1952. The smoke-like pollution was so toxic it was even reported to have choked cows to death in the fields. It was so thick it brought road, air and rail transport to a virtual standstill. This was certainly an event to remember, but not the first smog of its kind to hit the capital.

Smog had become a frequent part of London life, but nothing quite compared to the smoke-laden fog that shrouded the capital from Friday 5 December to Tuesday 9 December 1952. While it heavily affected the population of London, causing a huge death toll and inconveniencing millions of people, the people it affected were also partly to blame for the smog.

During the day on 5 December, the fog was not especially dense and generally possessed a dry, smoky character. When nightfall came, however, the fog thickened. Visibility dropped to a few metres. The following day, the sun was too low in the sky to burn the fog away. That night and on the Sunday and Monday nights, the fog again thickened. In many parts of London, it was impossible at night for pedestrians to find their way, even in familiar districts. In The Isle of Dogs area, the fog there was so thick people could not see their feet.

A history of smog

How the smog of 1952 formed

Impacts of the smog

Response to the smog

A history of smog

Britain has long been affected by mists and fogs, but these became much more severe after the onset of the Industrial Revolution in the late 1700s. Factories belched gases and huge numbers of particles into the atmosphere, which in themselves could be poisonous. The pollutants in the air, however, could also act as catalysts for fog, as water clings to the tiny particles to create polluted fog, or smog.

When some of the chemicals mix with water and air, they can turn into acid which can cause skin irritations, breathing problems, and even corrode buildings. Smog can be identified easily by its thick, foul-smelling, dirty-yellow or brown characteristics, totally different to the clean white fog in country areas.

There are reports of thick smog, smelling of coal tar, which blanketed London in December 1813. Lasting for several days, people claimed you could not see from one side of the street to the other. A similar fog in December 1873 saw the death rate across London rise 40% above normal. Marked increases in death rate occurred, too, after the notable fogs of January 1880, February 1882, December 1891, December 1892 and November 1948. The worst affected area of London was usually the East End, where the density of factories and homes was greater than almost anywhere else in the capital. The area was also low-lying, making it hard for fog to disperse.

How the smog of 1952 formed

The weather in November and early December 1952 had been very cold, with heavy snowfalls across the region. To keep warm, the people of London were burning large quantities of coal in their homes. Smoke was pouring from the chimneys of their houses.

Under normal conditions, smoke would rise into the atmosphere and disperse, but an anticyclone was hanging over the region. This pushes air downwards, warming it as it descends. This creates an inversion, where air close to the ground is warmer than the air higher above it. So when the warm smoke comes out of the chimney, it is trapped. The inversion of 1952 also trapped particles and gases emitted from factory chimneys in the London area, along with pollution which the winds from the east had brought from industrial areas on the continent.

the great smog
1950s car driving in thick smog

Early on 5 December, in the London area, the sky was clear, winds were light and the air near the ground was moist. Accordingly, conditions were ideal for the formation of radiation fog. The sky was clear, so a net loss of long-wave radiation occurred and the ground cooled. When the moist air came into contact with the ground it cooled to its dew-point temperature and condensation occurred. Beneath the inversion of the anticyclone, the very light wind stirred the saturated air upwards to form a layer of fog 100-200 metres deep. Along with the water droplets of the fog, the atmosphere beneath the inversion contained the smoke from innumerable chimneys in the London area.

great smogDuring the period of the fog, huge amounts of impurities were released into the atmosphere. On each day during the foggy period, the following pollutants were emitted: 1,000 tonnes of smoke particles, 2,000 tonnes of carbon dioxide, 140 tonnes of hydrochloric acid and 14 tonnes of fluorine compounds. In addition, and perhaps most dangerously, 370 tonnes of sulphur dioxide were converted into 800 tonnes of sulphuric acid.

 

Impacts of the smog

The fog finally cleared on December 9, but it had already taken a heavy toll.

  • About 4,000 people were known to have died as a result of the fog, but it could be many more.
  • Many people suffered from breathing problems
  • Press reports claimed cattle at Smithfield had been asphyxiated by the smog.
  • Travel was disrupted for days

Response to the smog

A series of laws were brought in to avoid a repeat of the situation. This included the Clean Air Acts of 1956 and 1968. These acts banned emissions of black smoke and decreed residents of urban areas and operators of factories must convert to smokeless fuels.

People were given time to adapt to the new rules, however, and fogs continued to be smoky for some time after the Act of 1956 was passed. In 1962, for example, 750 Londoners died as a result of a fog, but nothing on the scale of the 1952 Great Smog has ever occurred again. This kind of smog has now become a thing of the past, thanks partly to pollution legislation and also to modern developments, such as the widespread use of central heating.

Web page reproduced with the kind permission of the Met Office

Case Study – Severe Winters

Severe Winters

The list below may look like something that would happen in the Arctic, but all of them happened in the UK during two particularly severe winters — in 1947 and 1963.

  • Thousands of people cut off in their villages by snowdrifts up to seven metres deep.
  • Frozen rivers, lakes and even blocks of ice at sea.
  • Snow covering most of the land every day for more than two months.

Serious snowfall in the winter of 1947

The winter of 1963 — the coldest for more than 200 years

Serious snowfall in the winter of 1947

Thousands of people were cut off for days by snowdrifts up to seven metres deep during the winter of 1947, which saw exceptional snowfall. Supplies had to be flown in by helicopter to many villages, and the armed forces were called in to help clear roads and railways.

Between January and March that year, snow fell every day somewhere in the country for 55 days straight. Much of this settled because temperatures stayed very low, just above freezing most days.

No-one expected this winter to be severe, as January started with very mild temperatures at up to 14 °C recorded. This was soon to change, however. An area of high pressure moved over southern Scandinavia, setting up a weather pattern which dominated the UK for the rest of the month. The first snow came on 23 January, falling heavily over southern England. Blizzard conditions occurred across the south-west of England, leaving many villages in Devon isolated.

The cold, snowy weather continued through February and into March. Any breaks in the cold weather were short-lived.

  • In February, the temperature at Kew Observatory did not go over 4.4 °C and the night minimum temperature only went above 0 °C twice.
  • The mean maximum temperature for the month was 0.5 °C (6.9 °C below average) and the mean minimum was -2.7 °C (4.6 °C below average).
  • Mean minimum temperatures were more than 4 °C below average everywhere in southern England, and almost 6 °C below average in some places.

February 1947 was the coldest February on record in many places. One notable feature of this month was the lack of precipitation in parts of western Scotland. Because of the persistent anti-cyclonic conditions, some places that were normally very wet had no rain at all. A completely dry month in western Scotland is unusual. It was unprecedented in February.

Another unusual feature of February 1947 was the lack of sunshine in the Midlands and south of England — a complete contrast to the north-west of Scotland, where the weather was unusually sunny.

  • At Kew, Nottingham and Edgbaston, there was no sun on 22 of the month’s 28 days.
  • Most of the Midlands and southern England had sunshine totals about 40% of the average.

When skies did clear, night-time temperatures plunged. Woburn in Bedfordshire registered a low of of -21 °C early on 25 February.

If February hadn’t been bad enough, March was even worse. In the first half of the month, there were strong gales and heavy snowstorms, making for blizzard conditions. On 4 and 5 March, heavy snow fell over most of England and Wales, with severe snow drifts forming. On 6 March, drifts were five metres deep in the Pennines and three metres deep in the Chilterns.

On 10 and 11 March Scotland had its heaviest snowfall of the winter, with snow drifts up to seven metres deep reported by 12 March. The snowstorm heading over Scotland was to be the last over the UK for this cold spell, however. As it moved away, temperatures were already rising in the very south west of the UK. Temperatures rapidly got up to about 10 °C, and the leftover snow began to thaw rapidly. This created a serious problem. The ground was still frozen solid due to the weeks of cold weather, leaving the melting snow with nowhere to go.

As the warmer weather moved across the UK, the melt-water poured into rivers and caused many to burst their banks. Flooding problems began to spread across England from the south west, as a new depression came in from the Atlantic, bringing rain and severe gales. During the afternoon of 16 March, winds over southern England averaged about 50 knots, with gusts of 80–90 knots. This caused damage to buildings and caused even more problems as the strong winds created waves which pounded and even broke some flood defences.

River levels continued to rise. The banks of the Trent burst at Nottingham on 18 March and hundreds of homes were flooded, many to first floor level. While floods in the south-west England began to subside, other rivers continued to rise in eastern England. The Wharfe, Derwent, Aire and Ouse all burst their banks and flooded a huge area of southern Yorkshire. The town of Selby was almost completely under water. Only the ancient abbey and a few streets around the market place escaped inundation. Seventy per cent of all houses in the town were flooded. The flooding issues continued into the spring, bringing a nasty end to the cold and snowy winter.

In pictures

Boats frozen in ice on Poole Harbour in 1963 (courtesy of M. Nimmo)
Boats frozen in ice on Poole Harbour in 1963 (courtesy of M. Nimmo)
Skiing at Bulbarrow in Dorset in 1963. (courtesy of M. Nimmo)

The winter of 1963 — the coldest for more than 200 years

With temperatures so cold the sea froze in places, 1963 is one of the coldest winters on record. Bringing blizzards, snow drifts, blocks of ice, and temperatures lower than -20 °C, it was colder than the winter of 1947, and the coldest since 1740.

It began abruptly just before Christmas in 1962. The weeks before had been changeable and stormy, but then on 22 December a high pressure system moved to the north-east of the British Isles, dragging bitterly cold winds across the country. This situation was to last much of the winter.

A belt of rain over northern Scotland on 24 December turned to snow as it moved south, giving Glasgow its first white Christmas since 1938. The snow-belt reached southern England on Boxing Day and parked over the country, bringing a snowfall of up to 30 cm.

A blizzard followed on 29 and 30 December across Wales and south-west England, causing snowdrifts up to 6 m deep. Roads and railways were blocked, telephone lines brought down, and some villages were left cut off for several days. The snow was so deep farmers couldn’t get to their livestock, and many animals starved to death.

This snow set the scene for the next two months, as much of England remained covered every day until early March 1963. While snow fell, and settled there was still plenty of sunshine. The weak winter sun did not warm things up, however, as the lack of cloud cover allowed temperatures to plunge. In Braemar in Scotland, the temperature got down to -22.2 °C on 18 January. Mean maximum temperatures in January were below 0 °C in several places in southern England and Wales, more than 5 °C below average. Mean minimum temperatures were well below freezing. Temperatures weren’t much higher for most of February.

The long bitterly cold spell caused lakes and rivers to freeze, even sea water in some of England’s harbours turned to ice. Ice patches formed at sea and on beaches. Winter didn’t fully relax its grip until 4 March, when a mild south-westerly flow of air reached the British Isles. By 6 March, there was no frost anywhere in the British Isles and the temperature in London reached 17 °C — the highest since October 1962.

Finally, the coldest winter for more than 200 years in England and Wales had ended. With the thaw came flooding, but nothing like the scale of the 1947 floods. Soon after the winter had ended, life returned to normal.

Web page reproduced with the kind permission of the Met Office.

Case Study – Heatwave July 2013

A heat wave affected most of the UK from 3 to 23 July 2013, making this the warmest and sunniest July for the UK as a whole since 2006, and the third warmest on record. The Met Office issued a level three heat wave alert.

Meteorological situation

Below is the weather chart for 12:00 on Friday, 19 July 2013: there is high pressure over the UK.

High pressure generally results in a stable atmosphere and settled weather, and in the summer this can lead to warm temperatures. In July 2013 high pressure became established over the UK for much of the first two-thirds of the month.

july 2013 heatwaveLeft is a visible satellite picture of the British Isles from 19 July 2013 – a photograph taken from a satellite orbiting at an altitude of around 800 km. What is notable about this particular image is the amount of the UK without cloud cover. There is unbroken sunshine across much of the UK. You can also see smooth edged cloud on the coast of East Anglia and to the west of Scotland. This is low cloud called stratus, a typical cloud formation that occurs where moist air at low altitudes is cooled to the point that it saturates. When its base is near the surface, it becomes fog. During July the easterly winds often brought stratus inland along the east coast, so it did not get quite as hot here.

What caused the hot weather?

The seeds of the July hot spell were sown in June. Although June 2013 was not an exceptionally warm month, it was the lack of rainfall that was important. Because the ground was dry, it quickly warmed up in any strong July sunshine and in turn transferred the warmth to the air above it.

A weak cold front moved south-east across Britain during the 4th, with pressure building to the rear so that an area of high pressure formed over southern Britain on the 5th. Apart from some patches of low cloud near eastern coasts, inland there was hardly any cloud to stop the strong July sunshine from heating up the dry ground and therefore warming the air above it. The light winds also meant the heat didn’t disperse.

The hottest day was on the 22nd when the temperature reached 33.5 °C at Heathrow and at Northolt, both on the west side of London. By this time the airflow was blowing in from the south-east. Temperatures over northern France were as high as 30-35 °C in the days leading up the 22nd, and this very warm air transferred slowly into south-east England. A combination of dry ground, very warm air imported from northern France, a build up of heat from the previous days, and the fact that the south-east flow enabled the already warm air to travel over the built up area of London and heat up a little more, led to the high temperatures recorded on the west side of London. The hot spell broke down between the 22nd and 23rd as some heavy thundery rain spread from the west.

In a historical context, this hot spell was not particularly unusual. The length of it was the more notable feature, especially when put in the context of the run of rather changeable summers since 2007. This was the most significant heat wave since that of July 2006 (also dominated by high pressure and preceded by a dry June).

Getting the message to people

Heat Health Watch Service

The Met Office’s Heat Health Watch Service is designed to alert customers and the general public to the likelihood of heat wave conditions in different government regions of England, shown below in green:

There are four levels of the watch; one of the four levels will always apply from 1 June to 15 September each year. There are set daytime and overnight temperature thresholds which vary for each region. If there is a high chance (greater than 60 per cent) that these values will be reached on at least two consecutive days and the intervening night, then a higher watch level will be triggered.

In July a level three heat watch was issued; a level three is issued when the temperature threshold values for one or more regions has been reached the previous day and following night, and there is 90 per cent or more confidence that the threshold values in those regions will be exceeded during the next day.

The Met Office’s use of social media to get the message across

The Met Office has several of its own Twitter accounts (@metoffice; @metofficewarnings; @metofficenews) that are manned 24 hours a day, seven days a week. They not only respond to weather questions posted by the general public but also make people aware of the general weather forecast and any warnings that may have been issued by forecasters. This includes the Heat Health Warning Service, and several times during the July heat wave the @metoffice Twitter account was used to tell users about any current Heat Health alert levels for any of the nine regions.

 

Impacts

The July 2013 heat wave had both positive and negative impacts on people.

In the UK we are not used to such prolonged spells of warm weather, so it can be bad for people’s health, particularly for high risk groups such as young children and the elderly.

The hot, dry weather also raised the risk of fire, and there was a spate of wild fires in London as well as blazes elsewhere.

But these negative impacts should not take away from the generally buoyant mood that the warm, settled weather created, and the boost to tourism. The south-west of England, a tourist hotspot, had over 300 hours of sunshine during July.

Further information

http://metofficenews.wordpress.com/2013/07/ – The Met Office blog has several posts about the July heat wave.

The Met Office Weather Observations Website . You can see that the hottest day was 22 July.

Web page reproduced with the kind permission of the Met Office

Case Study – January Snow 2013

A snowy spell of weather affected most the UK from 14 to 26 January 2013.

This period brought the most widespread and prolonged snowfall in the UK since November and December 2010 and led to travel disruption and school closures across many parts of the country. All areas, apart from the far southwest of England, were affected.

Meteorological situation

Snow affected eastern Scotland and the north and east England on the 14 and 15 January.
10 cm was recorded in places. A cold few days followed and temperatures as low as -13.1 °C were recorded at Marham in Norfolk on 16 January.

On the 18 January a series of Atlantic weather fronts attempted to introduce milder air to the UK. With high pressure centred over Scandinavia, cold air from the east had been affecting the UK. With these fronts encountering such cold air, the precipitation fell as snow.

Image 1 below is the weather chart for 6am 18 January.

Image 2 below shows the weather radar for the same time and shows where the snow was falling. On the weather radar image the brighter colours show heavier snowfall. To see the weather radar intensity colour scheme go to www.metoffice.gov.uk/weather/uk/radar/
25 cm of snow fell across parts of south Wales and 5 to 15 cm fell widely across England
and Wales.

jan snow

Further snowfalls affected southeast and eastern England on the 19 and 20 January.

Parts of Scotland and Northern Ireland had significant falls too.

Image 3 below shows the snow depths (cm) on 20 January.

On 21 January northeast England and eastern Scotland had the heaviest falls of snow and strong southeasterly winds gave blizzard conditions in places. Parts of Northern Ireland were also affected by heavy snow.

Image 4 below shows the weather chart for 12pm on 21 January. Milder air was to the southwest of the UK and cold easterly winds affected the north. The weather front across northern England represents a battle between warm and cold air. The thin black lines (isobars) are lines of equal pressure. Closer spaced isobars give stronger winds.

january snowAnother fall of snow affected southwest England and south Wales on the 22 and 23 January as mild Atlantic air battled with the existing cold air. A final period of snow affected the Midlands northwards on the 25 and 26 January. A further 20 cm fell in places. The snow eventually turned to rain on 26 January with milder southwesterly winds finally becoming established across the UK.
Unsurprisingly, there were low temperatures during this period. Day time temperatures reached 1 or 2 °C at best and overnight temperatures were typically in the range -2 to -5 °C.

The table below shows the snow depths recorded during this period.

Getting the message to people

For many years the public has accessed Met Office forecasts via the TV, radio and newspapers. Now, our social media accounts on Facebook, Twitter, YouTube, Google+ and our News Blog have helped people to access our weather forecasts and warnings. During this cold spell people accessed the Met Office web pages millions of times every day.

cars in snowOn 17 January our web pages were viewed over four million times, roughly four times more than normal. People were able to plan, prepare and protect themselves from the impacts of the snow, ice and cold. Our social content was viewed by the Scottish Government, Heathrow Airport and the Highways Agency to name just a few.

 

Impacts

The disruption caused across the UK was significant. The transport network was badly affected right across the UK.

In Northern Ireland the snow which fell on 21 January led to many motorists been stuck in their cars for many hours. Some vehicles were abandoned and there were several crashes. Numerous buses were cancelled and the M1 had to be closed for a time.

Many trains were either cancelled or severely delayed right across the UK. Heathrow airport had to cancel hundreds of flights during the wintry period. Some of the delays were due to poor visibility rather than amounts of lying snow.
Thousands of schools were closed. It’s estimated that on 21 January roughly 5,000 schools were closed across the UK.

Further information.
www.bbc.co.uk/news/uk-21115289
www.bbc.co.uk/news/uk-northern-ireland-21135436
www.bbc.co.uk/news/uk-21139972
www.bbc.co.uk/news/uk-scotland-21138319
www.bbc.co.uk/news/uk-wales-21145509

Web page reproduced with the kind permission of the Met Office

Case Study – Hurricane Sandy

New York and its history of storms

New York City is no stranger to the effects of tropical storms and hurricanes. In fact, being located on something of a meteorological crossroads, lying in the zone where cold, Canadian Arctic air masses meet the warm Gulf Stream current, the Big Apple is in the firing line for both extreme winter storms and tropical cyclones.

One particularly notable storm that hit New York is the blizzard of 11 March 1888, which is considered one the USA’s worst ever blizzards. As for hurricanes and tropical cyclones, a number of tropical cyclones have clipped New York as they worked their way northwards, three making a direct hit (or landfall) over New York City: the 1821 Norfolk and Long Island Hurricane, the 1893 New York Hurricane and Tropical Storm Irene in 2011. The 1938 New England Hurricane came very close, making landfall on nearby Long Island.

Meanwhile, several hurricanes and tropical storms have just clipped New York City, including Hurricane Agnes, which passed just west of New York in June 1972 and killed 24. Hurricane Hazel brought record-breaking gusts of 113 mph to Battery Park, Manhattan Island, in October 1954. More recently Tropical Storm Floyd brought 60 mph winds and flash flooding to New York City in September 1999, whilst Hurricane Irene made landfall on Coney Island in August 2011, sparking the first-ever mandatory evacuation of coastal residents as a precaution.

2012’s Hurricane Sandy broke no wind or rainfall records in the Big Apple, but this massive hurricane proved one of the costliest ever to affect the USA. It brought winds up to 100 mph and widespread flooding from the associated storm surge. The surge flooded large parts of lower Manhattan, including subways and tunnels, caused mass power outages and destroyed thousands of homes and businesses, not just in New York but also in neighbouring New Jersey.

Some background on hurricanes and tropical cyclones

Before we look at how Sandy developed into one of New York City’s most notorious visitors it’s worth taking a closer look at some general aspects of tropical cyclones and hurricanes.

A tropical cyclone is the generic name given to a weather system over tropical or sub-tropical waters containing an organised area of thunderstorms, with cyclonic winds (anticlockwise in the northern hemisphere) around a low pressure centre. The tropical cyclone spectrum ranges from relatively small, weak storms called tropical depressions, with surface wind speeds less than 38 mph, to powerful hurricanes with surface wind speeds in excess of 160 mph. They are among the most dangerous natural hazards on earth and every year they cause considerable loss of life and damage to property.

Tropical cyclones typically start life over tropical oceans, forming when tropical thunderstorms are able to cluster and merge together in areas where the sea surface temperature is 27 ºC or more, where wind speed does not vary greatly with height and where winds near the ocean surface blow from different directions.

The sea provides a constant source of heat and moisture to ‘fuel’ the tropical cyclone. Winds near the ocean surface blowing from different directions help the warm, moist air rise and form cloud, and as wind speeds do not vary greatly with height, the cloud is able to grow into the giant thunderstorms.

When reaching land (known as ‘making landfall’), tropical cyclones will quickly tend to weaken because their ‘fuel source’ has been cut off. They will also weaken if they move over areas of cooler sea. Or they can weaken if wind speeds near the upper parts of the tropical cyclone cloud increase – ‘blowing’ the tops of the cloud downstream, destroying some of the cyclone’s organised structure and weakening it. Sometimes, however, a tropical cyclone will move away from the tropics and sub-tropics into the mid-latitudes and merge with existing mid-latitude weather systems. When this happens large and very powerful storms can form from the merger of the two systems.

There are various categories of tropical cyclone based on their wind speed. Weak tropical cyclones are called tropical depressions. When winds reach 39 mph they become known as tropical storms and they are then also given a name, which helps weather forecasters talk about them. Tropical cyclones can last more than a week and there can be more than one over any ocean at once, so giving them different names helps prevent confusion in weather forecasts. When winds reach 74 mph tropical storms over the Atlantic and north-east Pacific become known as hurricanes, and it is usually not until a storm becomes a hurricane that an ‘eye’ (an area of calm in the centre of a storm) becomes visible. In North America the Saffir-Simpson scale is used to categorise hurricane intensity – there are five categories and a hurricane is known as a ‘major hurricane’ if it reaches category 3 or higher.

Category

Max 1 minute sustained surface 10 m wind speed

Tropical depression

≤ 38 mph

Tropical storm

39-73 mph

Category one hurricane

74-95 mph

Category two hurricane

96-110 mph

Category three hurricane

111-129 mph

Category four hurricane

130-156 mph

Category five hurricane

≥ 157 mph

Table One: Categories of tropical cyclone.

tropical cyclone

Figure One: Tropical cyclone distribution (https://www.metoffice.gov.uk/research/weather/tropical-cyclones/facts).

Figure One shows where Atlantic hurricanes tend to occur. They usually take place between early June and late November, though a few have been known in both May and December. The peak in the Atlantic hurricane season is mid-August to around mid-October. Climatologically a powerful hurricane tracking close the USA’s eastern seaboard becomes more likely later in the summer and during the autumn; later in the year such storms will tend to be steered away north-eastwards into the Atlantic Ocean.

Typically tropical cyclones move forward at speeds of around 10 to 15 mph, though they can move both more slowly or much quicker, perhaps as fast as 40 mph under some circumstances. Movement can also be erratic, making forecasting their track even more challenging. A typical hurricane is around 300 to 400 miles in diameter, though as we shall see later they can be much bigger. The highest wind speeds will be wrapped around the core of the hurricane, extending out 25 to 50 miles from the core in smaller hurricanes, and 150 to 200 miles in larger ones.

The size of tropical cyclones is such that they will tend to steer around larger scale weather systems. In the case of Hurricane Sandy we shall see that this played an important role in determining her track.

The evolution of Sandy

hurricane sandy

Sandy started life as a cluster of thunderstorms which left western Africa on 11 October 2012 and moved westward to reach the Caribbean Sea on 18 October. This cluster of thunderstorms then gradually intensified to become a tropical storm on the 22nd. It moved towards Jamaica and on 24 October officially became a hurricane, called Sandy, just south of Jamaica. Sandy then moved across Jamaica, bringing with it winds up to 85 mph, before crossing eastern Cuba on the 25th. Sandy was at its most intense as it crossed eastern Cuba and moved towards the Bahamas, sustaining winds of around 115 mph. Sandy hit the Bahamas on the 26th and then weakened a little, briefly dropping back to a tropical storm before re-intensifying to a hurricane on the 27th. During the 26th and 27th Sandy was also able to grow much bigger in size whilst tracking almost parallel to the east coast of the USA.

An area of high pressure developing over Ontario on the 28th spread eastwards on the 29th and 30th, and acted as a block to Sandy’s path. Instead of curving north-eastwards into the Atlantic Ocean as many hurricanes do, Sandy was instead forced to turn north-westwards towards north-eastern USA. At the same time it interacted with a mid-latitude weather system which helped it to re-intensify and become much larger.

Sandy made landfall near Atlantic City, New Jersey, during the early evening of 29 October as one the most intense and damaging storms ever to affect the east coast of the USA. Sustained surface winds at landfall were close to 80 mph with gusts between 85 and 95 mph. After making landfall Sandy moved north-westwards, bringing heavy snow and blizzards to parts of the central Appalachian Mountains, and by the morning of 31 October no discernible storm centre could be found as the remnants of Sandy pressed on towards the Great Lakes and eastern Canada.

As Sandy was so big, wind damage covered a much larger area than would usually be expected from a hurricane. A larger area of strong winds led to a larger than usual storm surge. Sandy’s arrival into the US coast on the 29th also coincided with both high tide and spring tide, meaning that the tide would be at around its highest level. In New York City this added an extra 20 to 50 cm to the high water mark.

The extensive damage Sandy caused was the result of a number of unfortunate coincidences. It was able to grow particularly big, it was steered by the weather pattern developing over Canada, its landfall coincided with one of the highest tides of the month, worsening the impact of the storm surge, and it was pushed into the New York area rather than the less densely populated area further north.

Sandy’s impacts

hurricane sandy impacts

  • Impacts extended to Canada, Wisconsin and Lake Michigan down the eastern side of the USA into the Bahamas, Cuba, Haiti, the Dominican Republic and Jamaica.
  • At least 286 people were killed either directly or indirectly by Sandy. There were 147 direct deaths: 72 in the USA and the rest mainly in Caribbean, including 54 in Haiti and 11 in Cuba.
  • In the USA of the 87 indirect deaths from Sandy, at least 50 were attributable to either falls by the elderly, carbon monoxide poisoning from inadequately ventilated generators and cooking equipment, or hypothermia as a cold snap followed Sandy and extended power outages left people without heating.
  • Sandy was Cuba’s deadliest hurricane since 2005, whilst over the USA this was the greatest number of hurricane deaths from one storm outside of the southern states since Hurricane Agnes in 1972. Sandy was also the first hurricane to make landfall in Jamaica since 1988.
  • Sandy will go down as one of the USA’s costliest hurricanes. Damage estimates, based on 2012 values, will top $60 billion. In New York City economic losses are estimated at exceeding $18 billion.
  • Elsewhere damage estimates, again based on 2012 values, exceeded $30 million in the Dominican Republic, $100 million in Jamaica and $750 million in Haiti, as Haiti’s costliest hurricane on record. In Cuba damage estimates were around $2 billion, making it one of Cuba’s costliest ever hurricanes.
  • 346,000 houses were damaged or destroyed in New Jersey and 305,000 damaged or destroyed in New York and there were power outages from Indiana to Maine, with more than 8.5 million homes and businesses losing power. More than 18,000 flights were cancelled.
  • Sandy goes down as the largest hurricane on record in the Atlantic since at least 1988 in terms of diameter of gales. Among other meteorological ‘highlights’, Sandy brought 80 to 90 mph gusts over New York and New Jersey and its rain turned to heavy snow and blizzards over the Central Appalachians.
  • Sandy also brought heavy rain into north-east USA, the highest totals occurring south and west of New York City where typical amounts were around 25 mm whereas, for example, Washington DC had more than 125 mm and Niagara Falls close to 75 mm.
  • Record storm tides were also recorded in New Jersey, New York State and Pennsylvania coastal areas; in New York City, for example, the storm tide rose more than 4 m above mean low water, a record high storm tide for New York, beating the previous record set in 1960. Meanwhile, waves close to 10 m high were recorded in New York harbour, more than 2 m higher than the previous record, whilst waves just offshore New York were probably the largest in at least the last 40 or so years.

Web page reproduced with the kind permission of the Met Office

Case Study – Hurricane Katrina

At least 1,500 people were killed and around $300 billion worth of damage was caused when Hurricane Katrina hit the south-eastern part of the USA. Arriving in late August 2005 with winds of up to 127 mph, the storm caused widespread flooding. 

Physical impacts of Hurricane Katrina

Aftermath

Physical impacts of Hurricane Katrina

Flooding
Hurricanes can cause the sea level around them to rise, this effect is called a storm surge. This is often the most dangerous characteristic of a hurricane, and causes the most hurricane-related deaths. It is especially dangerous in low-lying areas close to the coast.

There is more about hurricanes in the weather section of the Met Office website https://www.metoffice.gov.uk/research/weather/tropical-cyclones/facts

Hurricane Katrina tracked over the Gulf of Mexico and hit New Orleans, a coastal city with huge areas below sea-level which were protected by defence walls, called levees. The hurricane’s storm surge, combined with huge waves generated by the wind, pushed up water levels around the city.

The levees were overwhelmed by the extra water, with many collapsing completely. This allowed water to flood into New Orleans, and up to 80% of the city was flooded to depths of up to six metres.

Hurricane Katrina also produced a lot of rainfall, which also contributed to the flooding.

In pictures

House and car destroyed by the hurricane
House and car destroyed by the hurricane
Flooded New Orleans street
Flooded New Orleans street
Boat on top of a house
Boat on top of a house

Strong winds
The strongest winds during 25-30 August were over the coastal areas of Louisiana and Florida. A map of the maximum wind speeds which were recorded during the Hurricane Katrina episode is shown. Although the winds did not directly kill many people, it did produce a storm surge over the ocean which led to flooding in coastal areas and was responsible for many deaths.

Satellite Image

hurricane katrina
Fig. 1 Satellite Image of Hurricane Katrina, 28 August 2005 at 2045 GMT. Courtesy NOAA/CIMSS/SSEC.

Illustration

Fig 2. Illustration showing different wave heights on a shoreline. Image courtesy of NOAA.
Fig 2. Illustration showing different wave heights on a shoreline. Image courtesy of NOAA.

Tornadoes
Hurricanes can create tornadoes. Thirty-three tornadoes were produced by Hurricane Katrina over a five-day period, although only one person died due to a tornado which affected Georgia.

Impact on humans

  • 1,500 deaths in the states of Louisiana, Mississippi and Florida.
  • Costs of about $300 billion.
  • Thousands of homes and businesses destroyed.
  • Criminal gangs roamed the streets, looting homes and businesses and committing other crimes.
  • Thousands of jobs lost and millions of dollars in lost tax incomes.
  • Agricultural production was damaged by tornadoes and flooding. Cotton and sugar-cane crops were flattened.
  • Three million people were left without electricity for over a week.
  • Tourism centres were badly affected.
  • A significant part of the USA oil refining capacity was disrupted after the storm due to flooded refineries and broken pipelines, and several oil rigs in the Gulf were damaged.
  • Major highways were disrupted and some major road bridges were destroyed.
  • Many people have moved to live in other parts of the USA and many may never return to their original homes.

Aftermath

The broken levees were repaired by engineers and the flood water in the streets of New Orleans took several months to drain away. The broken levees and consequent flooding were largely responsible for most of the deaths in New Orleans. One of the first challenges in the aftermath of the flooding was to repair the broken levees. Vast quantities of materials, such as sandbags, were airlifted in by the army and air force and the levees were eventually repaired and strengthened.

Although the USA is one of the wealthiest developed countries in the world, it highlighted that when a disaster is large enough, even very developed countries struggle to cope.

Weather Map

Fig 3. Map of America showing highest wind speeds. Image courtesy of NOAA.
Fig 3. Map of America showing highest wind speeds. Image courtesy of NOAA.

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Case Study – Hurricane Igor (Sept 2010)

A Met Office forecaster was working on secondment in Bermuda during
hurricane Igor. Some thoughts were gathered from somebody who experienced
it in person.

What is a hurricane?

A hurricane is a storm system which has a large low pressure centre. They produce heavy rain and have strong winds. To be classed as a hurricane the mean (as opposed to gust speeds) wind speeds must be in excess of 74 mph. The table below shows the Saffir-Simpson hurricane scale.

igot table

A hurricane with a wind speed of 74 mph is classed as a Category 1 hurricane. Category five hurricanes have wind speeds in excess of 155 mph. As well as heavy rain and intense wind hurricanes are traditionally accompanied by storm surges. Hurricanes form over warm tropical seas where the sea surface temperature is at least 27 °C. Moist air and converging winds are also required. Most hurricanes initially form to the west of Africa. As the hurricane develops it forms a clearly defined eye.

This satellite image shows Hurricane Igor.
The eye can clearly be seen as can the rain bands around it.

igor storm

On 17 September Bermuda was placed under a hurricane watch. It was feared that Igor would affect Bermuda as a Category three. On the 20 September Igor passed roughly 40 miles to the west of Bermuda. Winds reached sustained of 91 mph with gusts of 117 mph, in actual fact a Category one hurricane.

The impacts on Bermuda

Every year the Atlantic hurricane season spans from the start of June to the end of November.

Why was Igor in particular chosen for this case study? 

The reason is that Andy, a Met Office forecaster was on secondment with the Bermuda Weather Service and he experienced the full effects of the hurricane. It is good to get some thoughts from someone who experienced the effects in person.

“Hurricane Igor was predicted to be a direct hit on Bermuda. My job was to keep track of the forecasts and warnings for the Bermuda Weather Service, working closely with the National Hurricane Centre. This was exciting but the safety of the Islanders was always a concern. When the hurricane moved near, the noise in the weather centre became immense. The storm proof windows warped and there was a distinct smell of fish from the sea spray. Into the night there were flashes in the distance, which signalled the many downed power lines. Meanwhile reports came in of flooding in St Georges and some boats let loose from their moorings. When Igo finally cleared the Bermuda nobody was injured because they were prepared, thanks to the forecast and the action of government emergency agencies.”

photographing the storm

The main impacts were due to the winds which downed trees and as a result the power supply to around 28,000 people was cut. The airport was closed for 2 days. Several boats were broken from their moorings and damaged on rocks.

No evacuation plans were initiated but a school was converted into a shelter for anyone who felt unsafe. A small number of emergency rescues had to be made but thankfully nobody was hurt.

The main causeway between St David’s and St George’s islands was damaged and one lane was closed for several days.

Tourists were more apprehensive about staying on the island with the majority choosing to leave Bermuda a week or so before Igor’s arrival. A Royal Navy vessel was positioned offshore to assist if required during the hurricane and also in the post-hurricane recovery effort.

The damage was estimated to be less than $500,000. Officials believe that the biggest financial impact of Bermuda was vastly reduced income from tourism. With so many tourists choosing to leave Bermuda (and many cancelling their trips to Bermuda) during the run-up to Igor this had a major impact on hotel and restaurant trade etc.

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Case Study – Great Storm

The Great Storm of 1987

A powerful storm ravaged many parts of the UK in the middle of October 1987. 

With winds gusting at up to 100mph, there was massive devastation across the country and 18 people were killed. About 15 million trees were blown down. Many fell on to roads and railways, causing major transport delays. Others took down electricity and telephone lines, leaving thousands of homes without power for more than 24 hours.

Buildings were damaged by winds or falling trees. Numerous small boats were wrecked or blown away, with one ship at Dover being blown over and a Channel ferry was blown ashore near Folkestone. While the storm took a human toll, claiming 18 lives in England, it is thought many more may have been hurt if the storm had hit during the day.

The storm gathers

Warning the public

How the storm measured up

A hurricane or not?

The aftermath

The storm gathers

Four or five days before the storm struck, forecasters predicted severe weather was on the way. As they got closer, however, weather prediction models started to give a less clear picture. Instead of stormy weather over a considerable part of the UK, the models suggested severe weather would pass to the south of England – only skimming the south coast.

During the afternoon of 15 October, winds were very light over most parts of the UK and there was little to suggest what was to come. However, over the Bay of Biscay, a depression was developing. The first gale warnings for sea areas in the English Channel were issued at 6.30 a.m. on 15 October and were followed, four hours later, by warnings of severe gales.

At 12 p.m. (midday) on 15 October, the depression that originated in the Bay of Biscay was centred near 46° N, 9° W and its depth was 970 mb. By 6 p.m., it had moved north-east to about 47° N, 6° W, and deepened to 964 mb.

At 10.35 p.m. winds of Force 10 were forecast. By midnight, the depression was over the western English Channel, and its central pressure was 953 mb. At 1.35 a.m. on 16 October, warnings of Force 11 were issued. The depression moved rapidly north-east, filling a little as it went, reaching the Humber estuary at about 5.30 am, by which time its central pressure was 959 mb. Dramatic increases in temperature were associated with the passage of the storm’s warm front.

Warning the public

great stormDuring the evening of 15 October, radio and TV forecasts mentioned strong winds but indicated heavy rain would be the main feature, rather than strong wind. By the time most people went to bed, exceptionally strong winds hadn’t been mentioned in national radio and TV weather broadcasts. Warnings of severe weather had been issued, however, to various agencies and emergency authorities, including the London Fire Brigade. Perhaps the most important warning was issued by the Met Office to the Ministry of Defence at 0135 UTC, 16 October. It warned that the anticipated consequences of the storm were such that civil authorities might need to call on assistance from the military.

great stormIn south-east England, where the greatest damage occurred, gusts of 70 knots or more were recorded continually for three or four consecutive hours. During this time, the wind veered from southerly to south-westerly. To the north-west of this region, there were two maxima in gust speeds, separated by a period of lower wind speeds. During the first period, the wind direction was southerly. During the latter, it was south-westerly. Damage patterns in south-east England suggested that whirlwinds accompanied the storm. Local variations in the nature and extent of destruction were considerable.

How the storm measured up

Fig. 1 shows maximum gusts (in knots) during the storm.

Comparisons of the October 1987 storm with previous severe storms were inevitable. Even the oldest residents of the worst affected areas couldn’t recall winds so strong, or destruction on so great a scale.

  • The highest wind speed reported was an estimated 119 knots (61 m/s) in a gust soon after midnight at Quimper coastguard station on the coast of Brittany (48° 02′ N 4° 44′ W).
  • The highest measured wind speed was a gust of 117 knots (60 m/s) at 12.30 am at Pointe du Roc (48° 51′ N, 1° 37′ W) near Granville, Normandy.
  • The strongest gust over the UK was 100 knots at Shoreham on the Sussex coast at 3.10 am, and gusts of more than 90 knots were recorded at several other coastal locations.
  • Even well inland, gusts exceeded 80 knots. The London Weather Centre recorded 82 knots at 2.50 am, and 86 knots was recorded at Gatwick Airport at 4.30 am (the authorities closed the airport).

A hurricane or not?

TV weather presenter Michael Fish will long be remembered for telling viewers there would be no hurricane on the evening before the storm struck. He was unlucky, however, as he was talking about a different storm system over the western part of the North Atlantic Ocean that day. This storm, he said, would not reach the British Isles — and it didn’t. It was the rapidly deepening depression from the Bay of Biscay which struck.
This storm wasn’t officially a hurricane as it did not originate in the tropics — but it was certainly exceptional. In the Beaufort scale of wind force, Hurricane Force (Force 12) is defined as a wind of 64 knots or more, sustained over a period of at least 10 minutes. Gusts, which are comparatively short-lived (but cause a lot of destruction) are not taken into account. By this definition, Hurricane Force winds occurred locally but were not widespread.

The highest hourly-mean speed recorded in the UK was 75 knots, at the Royal Sovereign Lighthouse. Winds reached Force 11 (56–63 knots) in many coastal regions of south-east England. Inland, however, their strength was considerably less. At the London Weather Centre, for example, the mean wind speed did not exceed 44 knots (Force 9). At Gatwick Airport, it never exceeded 34 knots (Force 8).

The powerful winds experienced in the south of England during this storm are deemed a once in 200 year event — meaning they were so unusually strong you could only expect this to happen every two centuries. This storm was compared with one in 1703, also known as a ‘great storm’, and this could be justified. The storm of 1987 was remarkable for its ferocity, and affected much the same area of the UK as its 1703 counterpart.

Northern Scotland is much closer to the main storm tracks of the Atlantic than south-east England. Storms as severe as October 1987 can be expected there far more frequently than once in 200 years. Over the Hebrides, Orkney and Shetland, winds as strong as those which blew across south-east England in October 1987 can be expected once every 30 to 40 years.

The 1987 storm was also remarkable for the temperature changes that accompanied it. In a five-hour period, increases of more than 6 °C per hour were recorded at many places south of a line from Dorset to Norfolk.

The aftermath

Media reports accused the Met Office of failing to forecast the storm correctly. Repeatedly, they returned to the statement by Michael Fish that there would be no hurricane — which there hadn’t been. It did not matter that the Met Office forecasters had, for several days before the storm, been warning of severe weather. The Met Office had performed no worse than any other European forecasters when faced with this exceptional weather event.

However, good was to come of this situation. Based on the findings of an internal Met Office enquiry, scrutinised by two independent assessors, various improvements were made. For example, observational coverage of the atmosphere over the ocean to the south and west of the UK was improved by increasing the quality and quantity of observations from ships, aircraft, buoys and satellites, while refinements were made to the computer models used in forecasting.

Strength of gusts

Fig 1. Graphic showing areas with strengths of maximum gusts.
Fig 1. Graphic showing areas with strengths of maximum gusts.