Atlantic Tropical Depression Could Form in a Rare Location for So Late in the Hurricane Season

Chris Dolce
Published: October 14, 2019

A tropical depression or storm could form this week in a region of the Atlantic where development is rare this time of year.

The National Hurricane Center (NHC) says there is a high chance of a tropical depression forming before midweek from an area of low pressure centered southeast of the Cabo Verde Islands, or just off the western coast of Africa.

This system has been dubbed Invest 94L by the NHC, which is a naming convention used by meteorologists to identify disturbances that are being monitored for tropical development.

Stormy weather conditions are expected in the Cabo Verde Islands whether or not Invest 94L forms into a tropical depression.

Tropical development in October and November is most likely to occur west of 40 degrees west longitude. Development is most likely in parts of the western Caribbean Sea and Gulf of Mexico to the western Atlantic Ocean.

For reference, the far eastern portion of the yellow area in the North Atlantic part of the map below is very near 40 degrees west longitude.

Since 1851, just 10 tropical depressions or storms have formed near or east of 40 degrees west longitude for the nearly seven weeks spanning Oct. 11 through Nov. 30, according to historical records from the NHC. As you can see below, the area the NHC is monitoring for development this week is significantly farther east than the red dots depicting the origin points for those 10 tropical cyclones.

The white line depicts 40 degrees west longitude, and the red dots are origins near or east of there from Oct. 11 through Nov. 30. On the right side, the X shows the system being monitored for development into a tropical depression or storm this week.

A tropical storm here would be unprecedented in the satellite era for this time of year. No tropical storms have formed this far east in the tropical Atlantic Ocean so late in the season since satellites started tracking them in 1966.

The tropical Atlantic is a region of the North Atlantic Basin south of 23.5 degrees north latitude.

The farthest east a tropical storm has developed in the tropical Atlantic this late is 37 degrees west longitude, according to Dr. Phil Klotzbach, tropical scientist at Colorado State University.

That storm formed on Nov. 17, 1903. Since satellites did not exist until the mid-1960s, it's possible that the 1903 storm formed farther east than what's reflected in the historical record.

The reason this part of the Atlantic becomes less favorable for development late in the hurricane season is that tropical waves – one of the seeds for tropical storm development – become less defined as they move off Africa. Winds in the upper atmosphere also become less favorable for tropical storm formation.

If a tropical depression or storm does form this week, then upper-level winds will likely limit its long-term ability to survive. Therefore, this system poses no threat to any other land areas besides the Cabo Verde Islands.

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