April 6th, 2011

2011 North Atlantic Tropical Cyclone Season Forecasts

Posted at 11:25 AM ET

With the start of the 2011 Atlantic hurricane season just a couple of months away, tropical cyclone activity forecasts have started to emerge. AccuWeather, the Colorado State University (CSU) and Weather Services International (WSI) have released forecasts for the forthcoming hurricane season so far and there seems to be a general consensus that 2011 will see above-average activity. The most recent forecasts are summarised in the table below.

Summary of Hurricane Forecasts for 2011 (Source: AccuWeather, CSU, WSI)

Tropical Storms (>39 mph)

Hurricanes (>74 mph)

Major Hurricanes (>111 mph)

Average storm development (based on data from 1950 – 2009)




AccuWeather (released 30 March 2011)




CSU (released 6 April 2011)




WSI (released 22 December 2010)




Although an above-average 2011 season is forecast, hurricane activity is expected to be down compared to last year. The 2010 season was the third most active on record, with the formation of 19 named storms, 12 hurricanes and five major hurricanes. Despite this, there was little impact on the United States coastline. For the 2011 season, meteorologists said the main factors affecting the forecasts are the El Niño/La Niña-Southern Oscillation (ENSO), sea surface temperatures (SSTs), the positioning of the Azores/Bermuda high and dust coming off Africa.

When announcing its 2011 hurricane prediction on April 6, the CSU said it expected the 2011 season to be less active than 2010 as the current La Niña conditions are likely to transition to near-neutral ENSO conditions by the middle of the year. El Niño, a phenomenon marked by a warming of SSTs in the equatorial Pacific, tends to suppress the development of hurricanes (as demonstrated in 2009). Conversely, La Niña cools SSTs in the Pacific and typically enhances Atlantic basin activity (as seen in 2010). However, the CSU still expects the 2011 season to see above-average activity, with 16 named storms, nine hurricanes and five major hurricanes predicted.

The CSU said that the chances of at least one major hurricane making landfall in the United States in 2011 is 72 percent, notably higher than the long-term average of 52 percent. For the U.S. east coast, including the Florida Peninsula, the probability of a major hurricane making landfall is 48 percent, again up on the average of 31 percent. For the Gulf Coast, from the Florida Panhandle west to Brownsville, the probability is 47 percent, compared with a long-term average of 30 percent.

AccuWeather has also stated there is likely to be an increased risk of landfalling hurricanes along the U.S. mainland in 2011. Specifically, AccuWeather sees an early season landfall threat in the western Gulf of Mexico and the southern Caribbean, with the Texas and Louisiana coastline particularly vulnerable. The threat shifts into the U.S. southeast during the middle and late parts of the season, with a high probability of landfall along the Florida Peninsula and the Carolinas, AccuWeather said. AccuWeather added that northern New England and the Canadian Maritime provinces were likely to be threatened towards the end of season.

All forecasters seemingly agree on an increased landfall threat in the United States, with WSI also warning of enhanced landfall probabilities in the western Gulf of Mexico region in its December 2010 forecast. WSI said the forecast landfall numbers for the region were similar to those prior to the 2008 season, when hurricanes Dolly, Gustav and Ike pounded Louisiana and Texas. WSI’s next update for the 2011 hurricane season will be released on April 27.

Sources: Associated Press, Reuters News, Accuweather, Colorado State University, WSI Corporation

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Guy Carpenter publishes CAT-i reports for major natural catastrophes worldwide. These reports cover catastrophes including worldwide tropical cyclones, earthquakes, major UK and European floods and any other natural event that is likely to incur a significant loss to the (re)insurance industry. Please email CAT.i@guycarp.com if you wish to be added to the free email distribution list.

Guy Carpenter compiles RISK-i reports for major technological or man-made events worldwide. These reports cover risks to property, transport and life including explosions, fires, crashes, engineering disasters and terrorist attacks that are likely to incur a significant loss to the (re)insurance industry. Please email RISK.i@guycarp.com if you wish to be added to the free email distribution list.

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