The Met Office has confirmed it expects an active North Atlantic storm season this year – with a total of 20 tropical storms anticipated between July and November.

In a worrying development for coastal communities, the Met Office also revealed there is a 70 per cent chance there could be as many as 27 storms - well above the 1990–2005 long-term average of 12.4 storms per season.

Matt Huddleston, principal consultant on climate change at the Met Office said: “North Atlantic tropical storms affect us all through fluctuating oil, food and insurance markets.”

Accumulated Cyclone Energy

The Accumulated Cyclone Energy (ACE) index is a measure of the storm lifetimes and intensities as well as total numbers over a season.

This year’s most likely ACE index is 204; with a 70 per cent chance that the index will be in the range 90 to 319.

Again well above the 1990–2005 average of 131, and would make it one of the most active tropical storm seasons on record.

In the last 40 years only 2005 has seen more storms in the July to November period with 25 recorded, and only three seasons (1995, 2004 and 2005) have recorded a higher ACE index than 204.

For the past three years, the Met Office forecast has given good indication of Atlantic tropical cyclone activity and was able to identify the relatively quiet seasons of 2007 and 2009 from the active season of 2008.

“The Met Office forecast has demonstrated its benefits over recent years through the accuracy of its predictions,” added Mr Huddleston.

2010 Storm Season

This year the Met Office has moved to a new prediction system called GloSea4.

The new generation model has better representation of the complex physical processes that cause tropical storms and hurricanes to form, which should further improve 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.

Forecasts and background information on tropical storms can be found here.