It’s officially an El Niño season. That means that certain climate conditions have aligned. Sea surface temperatures are above normal in the east and central tropical Pacific Ocean and are expected to stay that way for at least several months, and air circulation in the atmosphere has shifted away from the “normal” state of rising in the usually warmer far western Pacific and flowing east to sink over the usually colder water in the east. The circulation reverses, with air rising in the east and sinking in the west to flow back east over the ocean, with lighter tradewinds.
Air circulation patterns work in tandem, and as a consequence of the Pacific reversal, the cycle of rising and sinking air has shifted in the Atlantic Ocean as well, and here, El Niño may interfere with the ability of tropical depressions to form hurricanes.
Because of this shift, NOAA forecasters with the Climate Prediction Center, a division of the National Weather Service, are predicting near-normal Atlantic hurricane activity for this year. The forecast is for 12 to 17 named storms with winds of at least 34 knots, with the possibility of five to nine becoming hurricanes with winds of 64 knots. Of those, one to four may become major hurricanes of category 3, 4 or 5, with winds of 96 knots or more. NOAA’s confidence in these ranges is 70 percent.
The chances of at least a moderate El Niño are 84 percent according to scientists on the The El Niño-Southern Oscillation blog team. Confidence is not 100 percent because other factors in the tropical Atlantic Basin could still change the risk of strong storm development. The potential for an above-normal West African monsoon and significantly warmer than normal sea surface temperatures are both part of long-term climate variations which have been conducive to and producing more active Atlantic hurricane seasons since 1995.