The National Hurricane Center has declared in their latest advisory that Subtropical Depression #1 has transformed into Tropical Depression #1. This is the fifth tropical depression (or stronger) tropical cyclone in the Atlantic hurricane basin on record in April. The Atlantic Hurricane Season doesn’t officially start until June 1.
In the latest update, the National Hurricane Center says Tropical Depression #1 was near latitude 36.1 North and longitude 40.0 West. The tropical depression is moving toward the northwest near 14 mph and this general motion is expected to continue until dissipation. Maximum sustained winds are near 35 mph with higher gusts. The estimated minimum central pressure is 996mb or 29.42″ of Mercury.
The tropical depression is forecast to be absored by a large extratropical low pressure system moving through the central Atlantic; as such, Tropical Depression #1 is likely to dissipate later tonight or tomorrow. Once it does, the National Hurricane Center will cease issuing advisories on it.
The overnight runs of the major American (GFS) and European (ECMWF) global weather forecast models show the the depression persisting as a well-defined, shallow low pressure system into Friday before it is absorbed by the aforementioned larger extratropical low. The combination of decreasing sea-surface temperatures and increasing southwesterly vertical wind shear ahead of the large extratropical low should act to steadily erode the associated convection, resulting in the depression weakening to a remnant low
pressure system by tonight, if not sooner.
The 2017 Atlantic Hurricane Season doesn’t officially start until June 1, but subtropical and tropical cyclones do pop up from time to time during the off-season. Leading hurricane forecasters believe this season will be slightly less active than normal; however, they also stress that it takes just one storm to create significant loss of life and property. Because this Subtropical Depression never became a named storm, the first named storm of the season will continue to be Arlene; the full list of names is here.