Tropical Depression Three is poised to develop in the Atlantic

July 29

In what seems like deja vu, exactly one week after Tropical Depression Two dissipated before our eyes, Tropical Depression Three is close to forming in almost the same location.  But this week, the environment is more favorable for it to strengthen.


Enhanced infrared satellite image of the central Atlantic from 10:15am EDT. (NASA)

This tropical wave exited the coast of Africa last Friday, and has been a feature of interest since then.  It has gradually become better organized, and despite its ragged appearance, it is in an environment that would allow it to intensify.  It’s centered about 1,500 miles due east of Trinidad, or about 1,900 miles east-southeast of Puerto Rico.

Currently, the vertical wind shear in the area is fairly strong, and not conducive for a tropical cyclone to form, but it is expected to relax later on Wednesday and remain low-to-moderate for several days.  The ocean temperature under the storm will stay in the 81-83°F range, which is warm enough to support even a strong hurricane. As far as the forecast goes, all models agree on it becoming a tropical storm within a day.  Some are little more aggressive and bring it up to minimal hurricane intensity by Friday, while the majority maintain a tropical storm for several days.  

The short-range track forecast is easy: maintain a west-northwest heading at about 12 mph for the next five days.  This will bring it near the Leeward Islands on Saturday and Puerto Rico on Sunday. Around that time, depending on its intensity, it could start interacting with an upper-level trough.  If it is weaker, it will be more likely to stay further south, but if it’s stronger, it will be more likely to get nudged northward and recurve east of the Bahamas.  

There is still plenty of time to refine this forecast, since the split in track scenarios doesn’t happen until early next week.


Ten-day track forecasts and probabilities from this morning’s run of the GFS model (AVNO), its 20-member ensemble (AP20), and the mean of the ensemble members (AEMN).  (B.Tang, UAlbany)

Coincidentally, the storm that provides a close analog for this one is Bertha from 1996.  The map below shows Bertha’s track in 1996, and the gray circle in the lower-right corner is where pre-TD3 is located today.  So not only would they form at virtually the same location, and during July, but the track forecast for the current system lies close to Bertha’s, at least for the next several days.

Track and intensity of Hurricane Bertha 1996. (NOAA)
Track and intensity of Hurricane Bertha 1996.  The current disturbance is located at the gray circle.  (NOAA)

Since the last depression never did reach tropical storm intensity and get named, I wanted to revisit the naming trivia now that Bertha appears extremely likely.  Bertha is one of the names from the original set of six lists started in 1979.  It was first used in 1984, so this year will be its sixth time around. And, 80 of the original 126 names (6 lists with 21 alphabetical names each, omitting Q, U, X, Y, Z) are still in use, while 53 names have been retired.  Want to guess which letter has had the most retirees?   This year’s list contains 12 of the original 21 names, and five of the six lists still have their original “B” name too!

(If you guessed “I” for the letter with the most retired names, pat yourself on the back!  Since 1979, there have been eight “I” names retired, while “F” comes in second place with six.  The only letter with no retirees is “V.”)

 

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Matt Rogers · July 29