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Monday, February 1, 2010

More Active 2010 Hurricane Season Expected

(Feb. 1) -- Even though it's the middle of winter, some private forecasters have already turned their meteorological brains toward the warm season, with forecasts for the 2010 Atlantic Basin hurricane season. WSI, a private forecasting company, and the Tropical Meteorology Project of Colorado State University (CSU) have both issued early season projections of more storms than last year -- and more storms than an average tropical season.

WSI is forecasting 13 named storms (tropical storms and hurricanes), including seven hurricanes, and three major hurricanes. A major hurricane is considered one of category 3 or higher, which is a storm with a sustained wind of at least 131 mph. CSU is forecasting 11 to 16 named storms, including six to eight hurricanes and three to five major hurricanes. The 50-year average is 9.6 named storms, 5.9 hurricanes, and 2.3 major hurricanes per year.

Whenever a long-range or seasonal weather forecast is issued, it's immediately followed by cries such as "They can't get the forecast right for tomorrow, but they think they get the forecast right for six months from now -- please!" While I understand the sentiment behind the statement, short- and long-range forecasts are done so differently that the statement has no relevance.

Hurricane Bill, here in a satellite image, churns in the Atlantic in August 2009.
An accurate short-range forecast is dependent on details -- what is happening now, and how it will change during the next hour, day, or week. A slight change in the wind flow, upper-level temperatures, or track of a specific storm can be the difference between a partly sunny day and non-stop rain or the difference between a chilly rain and heavy snow.

Long-range forecasts are not influenced by these small-scale factors. They're based on general, long-term weather factors, such as temperatures of the Pacific Ocean, temperatures of the Atlantic Ocean, and general position of large upper-level high- and low-pressure systems. The details, which can cause an embarrassing short-range forecast, don't influence the overall accuracy of a seasonal forecast.

There's no comparison between the two types of forecasts, and the ability -- or inability -- to make a quality short-range forecast has no bearing on the ability to make a quality seasonal forecast, such as a hurricane forecast.

The early season hurricane forecasts are based, in no small part, on El Nino, or more accurately, the anticipated lack of an El Nino during the upcoming summer. The presence, or development, of an El Nino during the hurricane season typically results in fewer storms in the Atlantic Basin (the Atlantic Ocean, Gulf of Mexico and Caribbean), which was the case in 2009, a particularly quiet season. The season following an El Nino, however, typically has an average or above-average number of storms.

While the El Nino is forecast to last at least into spring by the Climate Prediction Center, it is expected by these private weather forecasters to dissipate by summer, possibly setting the stage for a more active hurricane season. Other factors will influence the details of the season and the specifics of any seasonal forecasts issued later by these forecasters, other private forecasters, and the Climate Prediction Center.

At this point, though, the forecast of a more active hurricane season is reasonable.

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