Cyclone twins form in the Indian Ocean

April to June each year usually sees the transition from the southern to the northern hemisphere tropical cyclone season.

During this time it is possible to see cyclones in both hemispheres simultaneously. Furthermore, cyclone ‘twins’ sometimes develop at approximately the same longitude either side of the equator.

For the first time since 2009 cyclone twins have developed in the Indian Ocean.

This was caused by a strong burst of westerly winds along the equator about a week ago. A large mass of clouds located in the same area initially moved eastwards with the wind.

The clouds furthest from the equator then started to curl northwards in the northern hemisphere and southwards in the southern hemisphere due to the earth’s rotation. Over time these cloud masses have consolidated and started to rotate to produce twin tropical storms.

The southern hemisphere storm has been named Jamala and is currently not expected to affect any land areas.

The northern hemisphere storm has been named Mahasen and there is a stronger likelihood of this making landfall next week on one of the Bay of Bengal’s coastal regions.

Regional warnings for Tropical Storm Jamala are produced by the Tropical Cyclone warning Centre at La Réunion in the South Indian Ocean.

Regional warnings for Tropical Storm Mahasen are produced by the Tropical Cyclone Warning Centre at New Delhi, India.

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.

You can see the latest image of Tropical Storms Jamala and Mahasen at:

http://tropic.ssec.wisc.edu/real-time/indian/images/xxirm5bbm.jpg

2012 hurricane season comes to an end

This year saw another active season in the North Atlantic with 19 named storms, of which 10 became hurricanes.

Both the number of named storms and hurricanes were well above the 1980–2010 averages of 12 and six respectively. However, only one of these (Michael) became a major hurricane, which is below the average of three.

Unusual season

It has been an unusual season in many respects. This is the third year in a row with 19 named storms, which is unprecedented in the historical records. Only one other season – 2005, which saw the devastating Hurricane Katrina – has experienced more named storms (28) since reliable records began in 1944.

The season has also been notable for the high number of relatively short-lived storms, with seven of the nine tropical storms lasting just two days or less. These storms contribute towards a high storm count, but relatively little towards the Accumulated Cyclone Energy (ACE) index – a measure of the combined strength and duration of all named storms in the season.

Joanne Camp, a long-range hurricane forecaster at the Met Office, explained that having so many short-lived and relatively weak tropical storms was a notable feature of the season: “If you look at the long-term record, this is unusual – but it has been an increasing trend over recent years.

“It is almost certainly due to the improvement of technology, such as satellites, which allows us to observe developments over the North Atlantic in ever greater detail. This means that we are now identifying storms that could previously have gone undetected.”

Many storms – but not much power

Because such a high proportion of this season’s storms were short-lived and weak, the ACE index was only moderately above average at 127. The average is 104. Many seasons in the historical record have had a much lower total tropical storm count, but much higher ACE index,  for example the 2004 season recorded only 14 named storms but an ACE index of 225 – nearly twice  that seen in 2012.

The Met Office public forecast for the North Atlantic hurricane season, which is issued in May, continued its run of providing good guidance on the ACE index – with this year’s actual total well within the predicted range. On the number of storms, the total of 19 this year is outside of the forecast range.

Chris Landsea, Science and Operations Officer at the National Hurricane Center in Miami, said: “Because we are now better able identify weak, short-lived tropical storms than we were just 15 to 20 years ago, a simple count of how many storms occur in a season is perhaps not the most representative measure of how active a season has been. Using ACE index or number of hurricanes would be a more stable measure, less prone to changes in technology during the last 40-50 years.”

Experimental forecasts run by the Met Office during the 2012 season show that there is skill for forecasting the number of hurricanes. In May 2012 the Met Office predicted that the most likely number of hurricanes to occur during June to November 2012 would be six, with a 70% chance that the number would be in the range two to ten. In the event ten hurricanes occurred.

Significant storms

The most notable storm of the 2012 season was Hurricane Sandy (also referred to as Superstorm Sandy), which became one of the largest storms on record, measuring over 1000 miles across. The storm resulted in 253 deaths (at least 122 of those in the Caribbean) and is estimated to have caused over $65 billion in damage – making it the second most costly hurricane in US history, behind Hurricane Katrina.

GOES-13 natural-color image of Hurricane Sandy at 17:45 UTC on October 28, 2012. CREDIT: NOAA/NASA GOES Project.

The Caribbean also experienced a number of tropical storms during 2012 season. Hurricane Isaac caused severe damage in Haiti and eastern Cuba before making landfall along the northern Gulf Coast of the USA. Tropical Storm Rafael passed close to Puerto Rico and the British Virgin Islands. Hurricane Sandy made landfall over Jamaica and Cuba before heading to the northeast coast of the USA and Hurricane Ernesto made landfall over Central America.

No major hurricanes (those registering category 3-5 on the Saffir-Simpson hurricane wind scale) have made landfall in the US since Wilma in 2005 – a near-record length of time.

Longer-term trends

Overall the relatively high level of Atlantic hurricane activity continues a trend which started in 1995, with most years since then being above-average. To assess long-term cycles in North Atlantic hurricane activity the Met Office is trialling experimental forecasts for up to five years ahead.

While this research continues, the Met Office’s hurricane experts will continue to monitor the drivers of tropical storm activity over the next few months as they prepare the first forecast for next year’s season, which will be issued in March 2013. The main public forecast will be released in May 2013.

Further details on the 2012 season can be found in this year’s verification report (PDF, 1 MB).

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.

Typhoon Bopha on course for southern Philippines

Typhoon Bopha is set to bring strong winds and heavy rain to the island of Mindanao and other parts of the southern Philippines during Tuesday. Almost a year ago Tropical Storm Washi caused devastation in this region with the loss of over 1200 lives. Typhoon Bopha is far stronger and likely to make landfall in the same place at around midnight UK time.

Typhoon Bopha has already had an impact on the island republic of Palau causing a loss of power, wind damage and flooding, although the eye of the typhoon passed south of the main island sparing it from the worst effects. After a short period of weakening, Bopha has restrengthened to the equivalent of a category 5 hurricane and is likely to produce winds up to 150 mph and heavy rain as it makes landfall in the Philippines causing structural damage, flooding and landslides. Relief agencies are watching the situation closely, ready to respond to the unfolding situation.

Typhoon Bopha is one of the lowest latitude storms for many years. Tropical cyclones rarely form closer than about five degrees of latitude (500 km) from the equator. This is because the coriolis effect, which causes storms to spin, is not strong. However, Typhoon Bopha became a typhoon at just 3.8 degrees from the equator. This makes Bopha the lowest latitude typhoon since Typhoon Vamei in 2001. Bopha continued strengthening and went on to attain what some agencies refer to as ‘super typhoon’ status (1-minute mean winds near 150 mph). This occurred at 6.1 degrees from the equator – just 0.1 degree shy of the record set by Super Typhoon Kate in 1970.

Satellite image showing Typhoon Bopha 30th November 2012

Regional warnings for Typhoon Bopha are produced by the Japanese Meteological Agency (JMA) and the Philippine Atmospheric Geophysical and Astronomical Services Administration (PAGASA). The Met Office routinely supplies predictions of typhoon 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 Sandy heading for Jamaica and Cuba

It may be late October, but the Atlantic hurricane season is still in full swing. At this time of year the strongest storms usually develop in the Caribbean Sea and this is where Tropical Storm Sandy has been gathering strength in the last couple of days.

Sandy could reach hurricane strength before making landfall over Jamaica later today bringing winds of up to 75 mph and 150 to 300 mm rain. Sandy may not strengthen much once it hits the land but is then expected cross Cuba and the Bahamas, giving Haiti a glancing blow on the way.

Sandy is then likely move north and bring strong winds and torrential rain to southeast Florida for a time  before it develops into a deep Atlantic low pressure system with the possibility of bringing wet and windy conditions to north-eastern USA or eastern Canada early next week.

Further out in the Atlantic Tropical Storm Tony has developed. Although no threat to land, Tony is the 19th storm of the 2012 Atlantic season equalling the tally of both the 2011 and 2010 seasons.

Tropical Storms Sandy and Tony

Meanwhile, a tropical depression has developed in the Arabian Sea and looks set to bring rain to Somalia in eastern Africa in the next couple of days. If it does strengthen into a tropical storm, it will be the first storm in the northern Indian Ocean in 2012.

In the western Pacific Tropical Storm Son-Tinh is bringing wet and windy weather to the southern islands of the Philippines including Mindanao. This will bring back memories of last year’s Tropical Storm Washi which caused devastation in this region. Son-Tinh is likely to continue its track across the South China Sea and make a further landfall at the weekend over Vietnam or southern China.

Tropical Storm Son-Tinh

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 storm season heading towards its peak

August and September are the months when tropical cyclone activity in the northern hemisphere reaches its peak. As August begins there are currently several active tropical cyclones and possibly more to come.

Typhoon Saola formed in the west Pacific and gave a glancing blow to the northern Philippines. Over 900 mm rain in three days were recorded in Baguio. There were reports of flooding across northern Luzon and a number of fatalities. Saola has now slowly moved on towards Taiwan dumping similar amounts of rain and causing flooding and mudslides. It is expected to move onwards to Fujian province of China in the next day or so.

Meanwhile to the north of Saola the more compact Typhoon Damrey has tracked just to the south of Kyushu in south-west Japan. This area is still recovering from the devastating floods of last month. The typhoon has tracked across the Yellow Sea and is set to make landfall over the Handong province of China just south of the large city of Qingdao.

These two typhoons are part of a large complex area of disturbed weather covering much of the tropical western Pacific. Another storm is forming out at sea and latest forecast suggest it could track close to southern Japan in a few days time. There are even suggestions that yet another storm could develop a few days later in the open waters of the west Pacific.

Meanwhile in the Atlantic after an active start to the season, July was completely stormless. August has started with the formation of a depression which looks set to track through the Leeward Islands and into the Caribbean Sea. However, there is a high degree of uncertainty as to whether this depression will undergo significant strengthening. El Niño conditions are starting to develop as predicted by longer range forecasts for the tropics from the Met Office, which acts to suppress Atlantic tropical storm activity by making atmospheric conditions unfavourable. It is possible that conditions may be hostile towards storm development in this region in the next few days, but it is by no means certain.

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 just two tropical storms have occurred so far in this region.

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

Related articles

• Typhoons trigger flood alert (China Daily)
• Torrential rains wreak havoc in Taiwan (Todayszaman.com)
• Philippine floods persist, toll rises to 23 (channelnewsasia.com)

Met Office in the News: “Tropical Storms to hit Wimbledon”?

There have been several articles in the Daily Express over the last couple of days reporting ‘Summer is on the way at last’ with temperatures set to reach 34 Celsius this week and ‘Tropical storms set for Wimbledon’.

These headlines are unfortunately wide of the mark and rather misleading, both by implying that hot and sunny weather is on the way and that Wimbledon will be hit by tropical storms.

Although the Met Office has spoken to the Daily Express, the forecasts featured in the stories have not come from the Met Office, but from an independent forecaster.

The Met Office forecast for this week is for a couple of days of warm, humid and rather cloudy weather across much of the UK, with temperatures reaching 26 or 27 Celsius in any sunshine. For more detail you can find the latest weather forecast on our website.

It is our understanding that the temperatures of 34 deg C referenced in the articles are actually feels like temperatures taken from the website of an independent forecaster rather than actual air temperature. This is not made clear within the article and is potentially misleading.

The inference – through the lack of reference to the original source of the forecasts – that these forecasts have come from the Met Office is very misleading for the public, and potentially damages the reputation not only of the Met Office, but the wider weather forecasting community.

The Met Office is a world leader in meteorological science and our forecasts are recognised the world over as some of the best in the world. We are proud to be trusted to give the best possible guidance on the weather by the public and we report the weather exactly as it is.

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.