2015 tropical and Mid-Atlantic summertime outlook
Overall Summary: The overall numbers are likely to be down this year in terms of the number of Atlantic Basin tropical storms, but the sea surface temperature pattern in the western Atlantic and Gulf of Mexico makes the U.S. east coast vulnerable to “home-grown” tropical hits. The major factors involved with this year’s tropical outlook include a strengthening El Nino in the central equatorial Pacific, colder-than-normal waters off of the west coast of Africa, and pockets of warmer-than-normal temperatures in the Gulf of Mexico and also just off the US east coast. As a result, there are likely to be fewer-than-normal “African-wave” type tropical systems that travel long distances across the tropical Atlantic this season and more in the way of “home-grown” type systems that develop much closer to the U.S. Typically, the “African-wave” type storm plays an important role during the peak months of the tropical season (August and September) while “home-grown” systems can be important early and late in a given tropical season.
In a normal Atlantic Basin tropical season, there are about 12 named storms with 6 or 7 reaching hurricane status and only 2 or 3 actually reaching major status (i.e., category 3, 4 or 5). This year there may be more on the order of 8-10 named storms with 3-5 reaching hurricane status, but despite these expected slightly below-normal overall numbers, the U.S. could actually see more tropical activity than normal due to the sea surface temperature pattern in the western Atlantic and Gulf of Mexico.
One final note of interest, amazingly and fortunately, the US mainland has not been struck by a major hurricane (i.e. category 3 or higher) since Hurricane Wilma in October 2005. Although the landfall record gets muddy before the early 20th century, this is the first time since hurricane record-keeping began in 1851 that the United States has gone so long without at least a category 3 landfall. The previous streak was eight years, from 1861 to 1868.
El Nino in the tropical Pacific Ocean: What goes on in the tropical Pacific Ocean does indeed have an effect on the tropical Atlantic Ocean. El Nino, which refers to warmer-than-normal waters in the equatorial Pacific Ocean, affects global weather patterns and it tends to produce faster-than-usual high-altitude winds over the tropical Atlantic Ocean. This increase in the upper atmospheric winds over the tropical Atlantic Ocean is usually an inhibiting factor for tropical storm formation in the Atlantic Basin as it tends to “rip apart” developing storms. Currently, there are numerous signs for strengthening of the current El Nino in the tropical Pacific Ocean over the next few months and this should inhibit storm formation in the tropical Atlantic Ocean. Specifically, numerous computer forecast models support the idea that the current relatively weak equatorial El Nino strengthens this summer into moderately-strong status.