Met Office predicts above average Atlantic hurricane season

The Met Office Atlantic tropical storm forecast for 2013 is for 14 tropical storms between June and November, with a 70% chance that the number will be in the range 10 to 18.

The long-term average over the period 1980–2010 is 12 tropical storms. The last three hurricane seasons have all recorded above average tropical storm activity.

The most likely Accumulated Cyclone Energy (ACE) index — a measure of the strength and duration of storms over the season — is 130, with a 70% chance that the index will be in the range 76 to 184; the 1980–2010 average ACE index is 104.

For the first time this year, the Met Office are also releasing a forecast of the number of hurricanes (storms with winds of at least 74 mph), following the success of experimental forecasts produced throughout the 2012 hurricane season.

Between June and November 2013 the best estimate is for 9 hurricanes, with a 70% chance that the number will be in the range 4 to 14; the 1980–2010 average is 6 hurricanes.

Overall, these indicators point to a preference for above-average activity this year.

The evolution of the El Niño/La Niña cycle over the next few months is likely to play a large part in the North Atlantic hurricane season.

Joanne Camp, climate scientist at the Met Office, said: “El Niño conditions in the Pacific can hinder the development of tropical storms in the Atlantic whereas La Niña conditions can enhance tropical storm activity, so how these conditions develop will be important for the storm season ahead.”

The tropical storm forecast is produced using the Met Office’s new seasonal prediction system GloSea5. The model has higher resolution than its predecessor, with better representation of the complex physical processes that cause tropical storms and hurricanes. The forecast also uses information from the seasonal prediction system of the European Centre for Medium-Range Weather Forecasts (ECMWF).

For regular updates on tropical cyclones worldwide follow @metofficestorms on Twitter.

Cyclone Evan strikes Samoa

Towards the end of every year tropical storm activity moves from the northern hemisphere to the southern hemisphere. The South Indian Ocean has already spawned three tropical storms including the unusually strong early season Cyclone Anais in October. Attention has now switched to the South Pacific Ocean and Cyclone Evan.

Evan formed near Fiji a few days ago and moved north-east as it strengthened. As it reached the equivalent of hurricane intensity (winds near 75 mph) it made landfall over Samoa close to the capital city of Apia. Although winds of this strength are not exceptional for a cyclone, first reports indicate considerable wind damage and flooding from a storm surge of 12-15 feet (3.5-4.5 m). This storm surge is of similar height to that experienced in New York City during ‘Superstorm’ Sandy in October.

Visible satellite image of Cyclone Evan on 12 December 2012

Although Samoa lies within the cyclone belt of the South Pacific Ocean, the island nation has been relatively storm free for many years. Cyclone Heta passed close by in 2003, but the last time Samoa received direct strikes from tropical storms was in 1997 and 1998 by storms named Tui and, coincidentally, Evan.

To make matters worse, Cyclone Evan is expected to become slow moving near Samoa and American Samoa, producing large amounts of rainfall, before turning back south-west. Latest forecasts suggest Evan will strengthen some more and could threaten a strike on Fiji early next week.

Regional warnings for Cyclone Evan are produced by the Fiji Meteorological Service. The Met Office routinely supplies predictions of cyclone tracks from its global forecast model to regional meteorological centres worldwide, which are used along with guidance from other models in the production of forecasts and guidance.

You can keep up to date with tropical cyclones around the world on our website or follow us on Twitter.

Tropical Storm Isaac heads toward New Orleans

At 1500 UK time on Tuesday 28 August, Tropical Storm Isaac was located about 150 km southeast of the Louisiana coast and heading northwest at about 15 km per hour.  Mean wind speeds of 70 mph at the surface  have been observed by the United States National Hurricane Center aircraft. These mean wind speeds maintain Isaac as a tropical storm, just below hurricane strength which requires mean wind speeds of over 74 mph.

Satellite image showing Tropical Storm Isaac (Source: NOAA)

Although Isaac is expected to make landfall within the next 12 to 18 hours, there is still time for Isaac to intensify and become a hurricane. The official United States National Hurricane Center (NHC) forecast track predicts an intensification of this system into a category 1 hurricane as it continues its track northwestwards over the very warm Gulf of Mexico with winds increasing to around 80 mph when Isaac makes landfall at around 0600 UK time on Wednesday morning. 

Official National Hurricane Centre Forecast for Isaac on Tuesday 28th August

The latest forecast from the NHC suggests that Isaac will pass just to the west of New Orleans, though there is still some uncertainty over the exact track and intensity of the storm and the impact of Isaac will be felt quite widely along the Gulf coast region.

Although hurricane Isaac is not expected to be as intense as hurricane Katrina which caused massive damage to New Orleans 7 years ago, there is still a risk of extreme rainfall with up to 500 mm in 48 hours resulting in flash flooding and storm surge along the coast, in addition to the damaging winds.  As Isaac moves inland it will weaken, but is still likely to result in torrential rain, perhaps with tornados or very squally winds.  There is a risk of flooding over the lower Mississippi valley region for the next few days.

You can find out more about Tropical Cyclones on our website or read our case study on Hurricane Katrina on the Met Office Education website. 

Tropical Strom Isaac likely to make landfall as Cat 2 Hurricane

Tropical Strom Isaac was located about 120km WSW of Key West at 4am (UK time) on Monday 27 August, and continues to move west north west. Mean wind speeds of 65 mph have been observed by the United States National Hurricane Center aircraft. These mean wind speeds maintain Isaac as a tropical storm, just below hurricane strength which requires mean wind speeds of over 74 mph.

Satellite image and forecast track of Tropical Storm Isaac from Met Office StormTracker

The official United States National Hurricane Center (NHC) forecast track predicts an intensification of this system into a hurricane as it passes across the very warm Gulf of Mexico by midnight tonight with a high risk that the Hurricane will be a Category 2 storm, with winds of around 100 mph when it makes landfall along the US Gulf coastline during the early hours on Wednesday morning.

Official National Hurricane Center forecast for Tropical Storm Isaac

The NHC notes that there is still a great deal of forecast uncertainty in exactly where Isaac will make landfall, with locations ranging from the Texas/Louisiana border eastward to the Alabama/Florida border. The most likely forecast track has the eye of the storm making landfall close to New Orleans, but the NHC state that it is important not to focus on the exact forecast track due to forecast uncertainties and the fact that significant hazards extend well away from the centre.

Therefore, there is a high risk of very rough, chaotic seas and hurricane force winds across the Gulf of Mexico impacting marine traffic and oil and gas production during the next few days. This will be followed by torrential rain, potentially as much as 500mm in 48 hours, causing flash flooding. There is also the risk of embedded tornados and more general hurricane force winds, with a storm surge and over topping waves along the Gulf coast from Alabama to central Louisiana, with New Orleans at an increased risk of being impacted than previously expected.

The Met Office’s StormTracker allows you to monitor all named storms around  the globe to evaluate risk and enables the comparison of past and present storms. It can be used with the official warnings and guidance from the National Hurricane Center and other Regional Specialised Meteorological Centres (RSMCs) who have responsibility for the issue of tropical cyclone warnings.

Does the jet stream affect hurricanes?

Many news and weather articles, including our own blog, have reported recently that the UK’s wet summer is caused by the jet stream being situated further south than usual for this time of year.

However, some have questioned whether there is a link between this and the hurricane activity seen so far in the Atlantic.

So how is the Atlantic hurricane season shaping up and has it been influenced by the weather at higher latitudes?

Atlantic hurricane season so far

The Atlantic hurricane season officially started on 1 June, but in 2012 it began early with two tropical storms, Alberto and Beryl, forming in May.

After a break of almost three weeks there were two more storms, Chris and Debby, in the latter part of June, with Chris becoming the first hurricane of the season.

Since then there has been another lull of almost three weeks in Atlantic tropical storm activity.

Has the Atlantic hurricane season been unusual?

In mid-July it is far too soon to make judgements about how unusual a hurricane season is likely to be based on activity so far. However, it was certainly unusual to see four tropical storms before the end of June as this has never been observed before in over 150 years of records.

The recent quiet spell in Atlantic hurricane activity is by no means unusual. Atlantic hurricane seasons are often characterised by bursts of activity followed by quiet spells.

The peak of activity usually runs from the second half of August through to October. Even in some years which turned out to be very active, early season activity was low.

For example, by this time in 2010 and 2011 there had been just one tropical storm. Each of these seasons ended up yielding a total of 19 storms.

Is the jet stream involved?

The jet stream which affects UK weather is much further north than where the majority of tropical storms develop and hence has no direct impact on their formation.

However, once a tropical storm develops and starts to move to higher latitudes the jet stream can influence where it ends up. For example, in September 2011 as Hurricane Katia moved northwards in the Atlantic it met a powerful part of the jet stream and was swept eastwards as a strong ‘post-tropical’ storm which brought stormy conditions to the northern UK.

Will it be an active hurricane season?

The Met Office seasonal forecast for Atlantic tropical storm activity issued in May predicted a near-average season with the most likely number of storms in the June to November period being 10. Since June two tropical storms have occurred so far (the two May storms fall outside of this prediction period).

One of the major influences on the season’s activity includes the existence of La Niña or El Niño conditions (natural cycles which affect sea temperatures in the equatorial east Pacific).

Having just come out of an extended period of La Niña conditions, forecasts suggests an El Niño could develop before the end of the current hurricane season.

This would suppress hurricane activity in the Atlantic by disrupting the airflow over the regions where they usually develop.

However, it is worth remembering that it is 20 years since the quiet El Niño influenced Atlantic hurricane season of 1992. Despite being a quiet season overall, it still managed to spawn the deadly and powerful Hurricane Andrew which brought devastation to parts of Miami in Florida.

For more information on tropical cyclones worldwide visit our web pages or follow @metofficestorms on Twitter.

How often do the remains of hurricanes affect the UK

Hurricane Katia, currently in the western Atlantic is set to steam due east towards the UK and is expected to reach our shores as a post tropical storm later in the weekend. With it will come the risk of severe gales and heavy rain to parts of the UK. The strength and depth of this September storm is quite unusual, but similar storms that originated as hurricanes have affected the UK in the last 20 years several times.

Hurricane Bill – 2009

You only have to look back as far as 2009 to find a storm that crossed the Atlantic. Hurricane Bill formed on August 15th and reached the UK as a post tropical storm on August 25th, bringing severe gales and heavy rain two days after being downgraded from a hurricane to a tropical storm.

The path of Hurricane Bill in 2009. The storm crossed the Atlantic as a post tropical storm pushing into the UK and Ireland

 

Alberto, Gordon and Helene – 2006

In 2006, three post tropical storms reached the UK. Alberto, Gordon and Helene all brought wet and windy weather to the UK. Alberto combined with a cold front to the west of the UK whilst Gordon brought record warm temperatures as tropical air pushed north across the UK, but also strong winds that brought down power lines in Northern Ireland.

Isaac and Leslie – 2000

These two post tropical storms both affected the British Isles as in the year 2000.

Hurricane Karl – 1998

Hurricane Karl made its way to affect parts of southern Britain as a post tropical storm in 1998.

Hurricane Lili – 1996 

Perhaps the most similar storm to Katia was in 1996 when the remains of hurricane Lili pushed across the UK just one day after being downgraded from a hurricane. The post tropical storm ran across Britain on 28th and 29th October. The storm brought gusts in excess of 90 mph, bringing widespread impacts across the UK and causing significant disruption.

Path of Hurricane Lili in 1996

Hurricane Katia – 2011

Katia is currently a category one hurricane off the east coast of the US and will run across the Atlantic through the weekend bringing the risk of severe gales and storm force winds in places later on Sunday and through Monday.

Although it is expected to be windy everywhere, it is uncertain as to exactly which parts of the country will see the very strongest winds and therefore you should stay up to date with the latest forecast warnings.

Hurricane Irene expected to make landfall in the US this weekend

Latest forecasts show Hurricane Irene is expected to make landfall on the eastern coast of the United States on Saturday.

It is due to pass over North Carolina before continuing up the coast, passing over New York City about a day later.

Irene, the first hurricane of this year’s North Atlantic tropical storm season, has already caused much destruction in the Bahamas with winds of up to 115 mph.

The Miami-based National Hurricane Center (NHC), is warning that Irene could bring 6-10 inches (150-250mm) of rain, with up to 15 inches (380mm) possible in places. It will also bring a powerful storm surge which could cause flooding in low lying areas.

Julian Heming, Tropical Prediction Scientist for the Met Office, said: “While Irene’s strong winds have the potential to cause damage, it is the amount of rainfall combined with the storm surge which are most likely to cause disruption.

“Although there will be slow weakening, we are expecting Irene to remain a powerful storm as it travels north along the US east coast.”

The Met Office is one of the key providers of hurricane forecast modelling to the NHC.

The latest location and forecast track of Irene can be viewed on the Met Office’s StormTracker, a tool specifically designed to monitor tropical storms. It provides an interactive global picture of current storm activity to help quantify risk and aid decision making.

Travel advice relating to Hurricane Irene.

 

Met Office issues Atlantic tropical storm forecast for the 2011 season

Our forecast for this year’s North Atlantic tropical storm season states it is likely to be quieter than 2010, with 13 tropical storms between June and November 2011, with a 70% chance that the number will be in the range 10 to 17.

This is very close to the 1980-2010 long-term average of 12, and is in contrast to 2010 which had a total of 19 tropical storms.

Tropical storm frequency forecast. June to November 2011

The most likely Accumulated Cyclone Energy (ACE) index – a measure of the storm lifetimes and intensities as well as total numbers over a season – is 151, with a 70% chance that the index will be in the range 89 to 212: well above the 1980-2010 average of 104.

Accumulated Cyclone Energy (ACE) Index forecast . June to November 2011

For the past four years, the Met Office forecast has given accurate guidance of Atlantic tropical cyclone activity, identifying the relatively quiet seasons of 2007 and 2009 from the active seasons of 2008 and 2010.

Matt Huddleston, Principal Consultant on climate change at the Met Office said: “North Atlantic tropical storms affect all of us through fluctuating oil, food and insurance markets. Seasonal and multi-year forecasts are the focus for key research at the Met Office and the benefits of that are being realised through the increasing accuracy of its predictions”.

This is the second year of operation of the Met Office’s new seasonal prediction system called GloSea4. The new generation model has better representation of the complex physical processes that cause tropical storms and hurricanes to form, thus improving the accuracy of the forecast. The forecast also uses information from the seasonal prediction system of the European Centre for Medium Range Weather Forecasts.

One of the key indicators for a tropical storm season is the El Niño Southern Oscillation (ENSO), which affects sea surface temperatures in the tropical Pacific and, remotely, conditions in the North Atlantic. It’s therefore vital to be able to accurately predict the ENSO cycle and GloSea4 has shown good skill in such predictions.

Met Office in the News: 26 November 2010

The cold and snow across the UK is being covered extensively with coverage including, Britain ‘faces 10-day wintry blast’ (mirror.co.uk), North-east UK struggles as snow blows in (independent.co.uk), Fresh snowfall amid ice warning (bbc.co.uk), Snowvember (thesun.co.uk) and Forecasters predict more snow in UK (bbc.co.uk).

Today on BBC Radio 4 reported how the Met Office have issued a report on how this year is shaping up to be the hottest year on record, and how global temperatures may have been under-estimated. Dr Vicky Pope, head of climate change at the Met Office, explained how we may be underestimating the rate of global warming.

BBC Radio 5 Breakfast (last 5 minutes) and BBC online also covered the story in Met Office says 2010 ‘among hottest on record’.

Other newspapers reported: World is growing warmer, but pace slows (ft.com), Global warming is slowing down, say scientists (dailymail.co.uk) and World is warming quicker than thought in past decade, says Met Office (guardian.co.uk).

Met Office scientists have been awarded the inaugural Lloyd’s Science of Risk Prize for our work on long range hurricane predictions that will help tackle the largest single cause of insured loss.

Dr. Doug Smith, Met Office specialist in decadal forecasting, was awarded the prize for Best Overall Paper as well as the Science of Risk Prize for the Natural Hazard category. He led research that demonstrated for the first time the capability of climate models such as the Met Office Decadal Climate Prediction System (DePreSys) extends successful storm activity forecasts beyond the current season, to provide predictions years ahead.  An interview with Doug Smith followed the story.

Met Office in the Media: 08 November 2010

The Times reports on a new piece of research published in Nature Geoscience which shows skill in being able to predict the frequency of tropical storms in the North Atlantic more than one season ahead.  This has significant benefit for the insurance and re-insurance industry who rely on this kind of information to support their business decisions. This research builds on another successful forecast of the number of North Atlantic tropical storms forecast for the 2010 season between July and November. We predicted the most likely number to be 20.  Hurricane Tomas, which affected Cuba and Haiti over the weekend was the 19th storm of the season.

The wet and windy weather, forecast by us last week, has also generated a lot of coverage. The Sun and Daily Mail both reported on the heavy rain and strong winds that affected the country overnight last night and through today. They reported on the risk of snow, although the risk was confined to the higher parts of northern England and Scotland.

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