Here's What Else We're Watching in the Atlantic

Jonathan Belles
Published: September 21, 2019

A wide look at the tropics

In addition to Tropical Storm Jerry, we're monitoring two tropical disturbances moving westward across the Atlantic Basin.

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The first system, a tropical wave dubbed Invest 99L by the NHC, has a high chance of development as it moves quickly westward toward the Windward Islands. The large tropical wave is expected to bring 1 to 3 inches of rain to the Lesser Antilles through Sunday.

In addition to rain, gusty winds are expected in the Leeward Islands.

The NOAA Hurricane Hunters found that this disturbance is a sharp tropical wave with no well-defined center of circulation in a flight through the system Saturday afternoon.

(MORE: What Is an Invest?

Invest 99L could become a tropical depression over the next few days as it passes through the northeastern Caribbean Sea. 99L is expected to turn northward toward Puerto Rico or the Virgin Islands on Tuesday.


A second area to watch, a tropical wave with bursting thunderstorms, will move off the African continent on Sunday.

Favorable environmental conditions, along with warm ocean temperatures, are expected to be in place across the tropical Atlantic as this wave moves westward.

(MORE: Why Tropical Waves Are Important During Hurricane Season

Several computer models are developing this into a tropical depression as the system rolls westward across the Atlantic this weekend into early next week.

The NHC said this system has a high chance of development early in the week ahead.


The next storm to be named will be given the name Karen. Hurricane season continues until Nov. 30.

The Tropics Usually Stay Hot Through the End of September

Activity in the Atlantic begins to wane as we head into October, but tropical storms and hurricanes can occur just about anywhere in the basin.

On average, four more tropical storms, three more hurricanes and one more Category 3 or stronger hurricane form on or after Sept. 21. Many of these come in late September and early October.

With the peak of hurricane season over, we usually begin to see a few changes heading into October.

First, we begin to watch closer to home once again for tropical genesis because cold fronts can again begin to reach the East Coast and Gulf of Mexico. These cold fronts can gain spin and usually already have moisture draped along them.

These cold fronts also help scoop up tropical storms and hurricanes and pull them northeastward.

Usually, this is a good thing. Tropical storms and hurricanes that develop in the open Atlantic and the eastern Caribbean are usually redirected away from most land masses, including the United States.

But this isn't always the case. On occasion, storms can brew closer to Central America or in the Gulf of Mexico and be steered toward the northeastern Gulf of Mexico, Cuba or the Bahamas.

Another change that begins to happen: the African wave machine begins to shut down.

Tropical wave activity typically peaks during September, but declines quickly into October as the Sahara Desert cools off.

Tropical waves are, in part, produced by the temperature contrast between the hot Sahara Desert and the relatively cooler forests of equatorial Africa. When the Sahara cools off, the waves are no longer produced.

Tropical waves can be produced as late as Halloween, but they become less potent as the year goes on.


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