Despite relative calm during the first two months of the 2010 hurricane season, unusually warm sea surface temperatures in the tropical and North Atlantic and the development of a La Nina event in the Pacific are still likely to produce as many as 18 named storms, including 10 hurricanes, five of them intense (Category 3 or greater), before the season ends Nov. 30, according to Colorado State University (CSU) forecasters.

The CSU team said it is maintaining its previous forecast for a “very active” Atlantic hurricane season (see Daily GPI, June 3) and anticipates a “well above-average probability” of a major hurricane making landfall in the United States and the Caribbean. The forecast, which is based on a model that utilizes 60 years of past data, “is predicting a very active season for the Caribbean,” it said.

The probability of a major hurricane making landfall along the U.S. coastline this year is 75% compared with the last-century average of 52%, according to the CSU forecast. There is a 64% probability of at least one major hurricane tracking into the Caribbean this year, and a 49% probability of at least one major hurricane making landfall on the Gulf Coast between the Florida Panhandle and Brownsville, TX.

La Nina conditions — an unusual cooling of ocean surface temperatures off the western coast of South America that is believed to have significant effects on North American weather patterns — have developed over the past couple of months and are expected to be present for several more months, CSU said. Near-record warm surface temperatures in the Atlantic and anomalously low sea level pressures that occurred across the tropical Atlantic in June and July also favor the creation of hurricanes, they said.

The consensus forecast for the 2010 hurricane season has pointed decidedly towards an unusually active season, with most forecasters pointing to La Nina as the primary indicator of tropical storm formation. The National Oceanic and Atmospheric Association has said it expects an increase in Atlantic hurricane activity this year with 14-23 named storms, including eight to 14 hurricanes, three to seven of them intense (see Daily GPI, July 16; May 28), while Chief Long Range Forecaster Joe Bastardi has said 2010 could be one of the most active seasons on record (see Daily GPI, May 20).

But WSI Corp., which had increased its Atlantic hurricane forecast three times this year, last month lowered its expectations from 20 named storms to 19, while keeping its prediction that there will be 11 hurricanes and five intense hurricanes (see Daily GPI, July 21). WSI warned that the new 2010 forecast numbers are still well above long-term (1950-2009) averages.

The first two named storms of the season, Hurricane Alex and Tropical Storm Bonnie, created little threat to Gulf of Mexico oil and natural gas production. A third named storm, Tropical Storm Colin, formed in the Atlantic earlier this week, but had collapsed by Wednesday morning while still about 150 miles east-northeast of the Leeward Islands, according to the National Weather Service (NWS). There is only about a 20% chance that the remnants of Colin will become a tropical cyclone again over the next couple of days, NWS said.

Bastardi has said that the weakening of El Nino — the warming of surface temperatures in the central and eastern equatorial Pacific Ocean — and the current La Nina event will influence weather across the United States this winter (see Daily GPI, Aug. 4).

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