The forecasters cited several reasons for their forecast of an active season:
1) Above-average sea surface temperatures (SSTs) in the eastern subtropical Atlantic and cooler-than-normal SSTs in the South Atlantic have weakened the Bermuda-Azores High. This has resulted in lower surface wind speeds over the tropical Atlantic, and these weak trade winds are expected to persist into hurricane season. Weak trade winds reduce the amount of evaporative cooling of the ocean, resulting in warmer SSTs and lower surface pressures during hurricane season. Hurricane like to form in an environment with low surface pressures and high SSTs.
2) Hurricane activity in the Atlantic is lowest during El Niño years and highest during La Niña or neutral years. The current strong La Niña event has begun weakening noticeably in the past few weeks. However, there is probably not time for a full-fledged El Niño event to replace it by hurricane season, and it is expected that we will have weak La Niña or neutral conditions this hurricane season. None of the computer models are forecasting a switch over to El Niño conditions this year (Figure 1). Keep in mind, though, that the accuracy of these long range models is poor, particularly for forecasts made in March and April.
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