US weather forecasters have increased their predictions for the number of named storms that will form in the Atlantic Basin this season and now expect an ‘above normal’ 2008 hurricane season.
The National Oceanic and Atmospheric Administration is now expecting between 14 and 18 named storms, including seven to 10 hurricanes and three to six major hurricanes of Category 3 or higher strength, it said Thursday.
In May the agency had predicted 12 to 16 named storms, including six to nine hurricanes and two to five major hurricanes. An average Atlantic hurricane season has 11 named storms, including six hurricanes and two major hurricanes.
The increase was attributed to atmospheric and oceanic conditions across the Atlantic Basin that favour storm development combined with strong early season activity.
‘Leading indicators for an above-normal season during 2008 include the continuing multi-decadal signal – atmospheric and oceanic conditions that have spawned increased hurricane activity since 1995 – and the lingering effects of La Niña,’ said Gerry Bell, lead seasonal hurricane forecaster at NOAA’s Climate Prediction Centre.
‘Some of these conditions include reduced wind shear, weaker trade winds, an active West African monsoon system, the winds coming off of Africa and warmer-than-average water in the Atlantic Ocean.’
Another indicator favouring an above-normal hurricane season is a very active July, the third most active since 1886, NOAA said. Even so, there is still a 10 per cent chance of a near normal season and a five per cent chance of a below normal season.
NOAA’s assessment came after forecasters at Colorado State University said earlier last week they were increasing their storm predictions from 15 to 17 named storms for the season. Researchers Philip Klotzbach and William Gray said they expect nine to become hurricanes and five to become intense hurricanes with sustained winds of 111mph or greater.
If their predictions hold it would signify a 190 per cent increase in storm activity, compared to what was experienced between 1950 and 2000. The long-term annual average over that period was 9.6 named storms, 5.9 hurricanes and 2.3 intense hurricanes.
The prediction called for above-average major hurricane landfall risk in the Caribbean.
‘We have increased our forecast because there has already been a very active early tropical cyclone season in the deep tropics and more favourable hurricane-enhancing sea surface temperature and sea level pressure patterns in the tropical Atlantic have developed,’ said Mr. Klotzbach, lead author of the forecasts.
‘The primary concern with our current very active seasonal forecast numbers is the continued ocean surface warming in the eastern and central tropical Pacific. Although it seems unlikely at this point, there is a possibility that a weak El Nino could develop by the latter part of the hurricane season. If this happened, it would likely reduce the number of late season tropical cyclones.’
The forecasters said there was 67 per cent chance of a major hurricane hitting the U.S coastline this season, up from the long-term average of 52 per cent.
Five named storms have formed in the Atlantic basin this season including Hurricane Dolly, which passed by Cayman as tropical-storm Dolly on 20 July, bringing with it wind gusts of around 33mph and 4.45 inches of rain.