Tropical Disturbance in Central Atlantic, Invest 99L, Likely to Develop and Head Toward Lesser Antilles

Bob Henson
Published: August 24, 2019

A tropical disturbance moving across the central Atlantic could strengthen into a tropical depression or tropical storm as it heads west toward the Lesser Antilles over the next several days.

This disturbance, dubbed Invest 99L by the National Hurricane Center, was centered in the deep tropics near 10 degrees north latitude, roughly 900 miles east of the Windward Islands.

(MORE: What Is an Invest?

National Hurricane Center Potential Development Area

Winds near the surface, as measured with a satellite-borne instrument called a scatterometer, showed on Friday that 99L already had a broad but weak low-level circulation.

Sea surface temperatures are warm ahead of 99L, and upper-level wind shear will be lighter. These factors would favor intensification.

However, the mid-level atmosphere is moderately dry around 99L, and that will, most likely, keep a brake on any rapid strengthening. If the storm can develop an inner core of moisture and keep it walled off from the dry air, more sustained intensification would be possible.

The National Hurricane Center gave 99L a 70% chance of becoming at least a tropical depression by Monday morning, with a 80% chance by Thursday.

On its predicted path, 99L would approach the Lesser Antilles by Tuesday.

It’s too soon to know if 99L will pose any threat farther west or northwest toward the Greater Antilles and/or the United States. Any such threat would most likely be one to two weeks away.

Prime Time and a Prime Location

99L is located in the heart of the deep Atlantic tropics, also known as the Main Development Region. Tropical storms and hurricanes are most common in this region from late July into September as tropical waves move off Africa and into the Atlantic.

Such tropical waves emerging off the west coast of Africa are often referred to as Cabo Verde systems because many of them pass near the Cabo Verde Islands.

These are the locations where tropical storms developed in the time frame of Aug. 21-31 during the years 1851-2015.

On average, the peak of hurricane season occurs in early September, according to the NHC.

Tropical storms and hurricanes are still possible all the way to the official end of the season (Nov. 30), and sometimes even beyond that point.

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