|After an abnormally warm winter across much of the United States and the globe, we now turn our attention to the upcoming tropical season. Several factors play a role in how active or inactive a hurricane season will be, including sea surface temperatures, wind shear, and dry air. This season, several indicators are pointing to the possibility of a weak/moderate El Niño developing during the second half of 2017, from August through December, with some model forecasts hinting at a shift to El Niño as early as June, according to NOAA’s latest NCEP ENSO outlook. Figure 1 shows sea surface temperatures at or below normal across the Bahamas and Western Atlantic and above average temperatures near the central and eastern equatorial Pacific, an indicator for El Niño.
Figure 1: Sea surface temperature anomaly chart for May 2017 (Click To Enlarge)
In the Atlantic, El Niño conditions can hinder the formation of tropical systems by increasing the amount of wind shear across the Tropical Atlantic. Wind shear causes squalls to become displaced away from the center of a tropical system, deterring the strengthening and development of the system. We expect that with a weak/moderate El Niño expected to occur this season, the number of named tropical systems this year will be at or just below the 30-year average (12 named storms), with approximately 10-12 named storms likely to develop over the season. The Tropical Meteorology Project at Colorado State University has released their prediction for the upcoming Atlantic tropical season. Citing the weak El Niño expected to occur, they are forecasting a below average year for tropical development, with 11 named storms expected to form in the Atlantic. This is just shy of the 30-year average of 12 named storms, and only 2 of these storms are expected to become a major hurricane. It is worth noting, however, that we have already seen one named system in the Atlantic basin this year – Tropical Storm Arlene, who formed out of a subtropical cyclone in the North Atlantic in late April. The East Pacific basin averages more named storms than the Atlantic basin per year, with an average of 16 named storms. This year, the abnormally warm sea surface temperatures off the coasts of Nicaragua and Honduras are indicative of an active season of tropical development. Additionally, while El Niño results in increased wind shear in the Atlantic, the warmer sea surface temperatures in the Pacific yield lower wind shear values. Tropical Storm Adrian has already gotten the ball rolling in the East Pacific, becoming the first named system in the basin. Adrian formed prior to the official start of the tropical season in the East Pacific, which began on May 15th. Due to this early start and the two important ingredients in place in our forecast, we can expect that tropics in the East Pacific will be active this year, with an above average number of named storms. Although a below-average number of systems is forecast in the Atlantic, one factor not considered is how many of these storms will make landfall or affect major shipping lanes. WRI will monitor all potential development this year to ensure safe and efficient routing, remaining ahead of the game with our in-house Tropical Lows to keep our clients informed and prepared.