Tropical Storm Danny formed in the Atlantic Ocean on Tuesday afternoon, the fourth named storm of the 2015 hurricane season. (NOAA)

Tropical Depression Four strengthened on Tuesday afternoon and is now Tropical Storm Danny with sustained 40 mph winds, says the National Hurricane Center. Danny, which is located about 1,600 miles east of the Windward islands in the eastern Caribbean, is forecast to strengthen into the first hurricane of the 2015 season on Thursday.

Though there’s no immediate threat to land from this storm, it will probably continue to track west toward the Caribbean over the next week.

The National Hurricane Center is forecasting Tropical Storm Danny to strengthen into a Category 1 hurricane on Thursday, and then intensify further into a Category 2 with sustained winds of 98 mph by Sunday.


(National Hurricane Center)

Tropical Storm Danny is the earliest fourth named storm since Dorian in 2013, which was named on July 24.

A fledgling storm at this time and location has a formidable pedigree. Looking back at all the August storms that have formed within 200 miles of where Danny is located, the list includes some infamous hurricanes that made landfall in the United States, such as David (1979); Allen (1980); Andrew (1992); and Frances (2004).


Tracks of previous storms that formed during August and within 200 miles of 96L’s current position. (NOAA)

Environmental conditions are as conducive for this storm as we’ve seen all summer — although that’s not saying much given how quiet this season has been so far. But the tropical storm is in a climatological sweet spot for tropical cyclone development.

The biggest factor working against Danny is a huge plume of very dry, Saharan air that surrounds it, especially to the north. Otherwise, the sea surface temperature in the Atlantic is plenty warm to fuel a storm, the wind shear is moderately low, and the low to mid-level humidity is high in the area of the storm. Depending on the track, however, the dry air and shear could both increase rapidly by the end of the weekend.


Infrared satellite image (gray) with a “Saharan air layer” product overlaid in shades of yellow-red. 96L is in the bottom right corner. (University of Wisconsin/CIMSS)