19 August 2023

Tropical Depression 6 forms, plus four areas of interest scattered across the tropical Atlantic

Right on the climatological clock, the tropical Atlantic has awakened.  There are FIVE features of interest peppered from the Bahamas to Africa.

In the map above, the current position of TD6 is the red circle, and the current positions of the four disturbances are the colored Xs (yellow for low probability of formation within a week, orange for medium, and red for high).  The hatched blobs indicate the areas of potential formation... they are not track forecast cones. Remember, those things have not become tropical cyclones yet and perhaps never will.

I'll begin with Tropical Depression 6 which is located about 700 miles east of the Leeward Islands.  This African easterly wave developed in a brief window of opportunity, and due to some strong vertical wind shear and dry air, it's not expected to intensify to a tropical storm, and NHC actually forecasts its dissipation by Monday, well before reaching the Leeward Islands.

Tropical Depression Six

Now let's move west to east across the basin.  The first disturbance is not an Invest yet, but will be 91L.  It's a disorganized mass of thunderstorms spawling over the western Bahamas, south Florida, and Cuba, slowly making its way westward.  Model guidance suggests it could acquire a closed surface circulation and become a tropical depression once it's in the Gulf of Mexico... but no models develop it into anything troublesome.

Given the all-time record warm water temperatures in the Gulf of Mexico though, we obviously can't tune it out completely.  Widespread areas of 32-33°C water is unheard of in the Gulf, but it's what we've got right now.  This system should reach southern Texas or northern Mexico on Tuesday.

The next feature is another African easterly wave, tagged as Invest 90L.  It's just crossing the Windward Islands on Saturday afternoon and should continue moving west through the Caribbean for another couple of days.  Then, there's agreement among the models that it will turn north toward Hispaniola.  After exiting the Caribbean on Wednesday-ish, it actually has a better chance of intensification, and will likely remain over the open ocean.

1600 miles east of Invest 90L is Invest 98L.  Similar to TD 6, this has a brief window in which environmental conditions will be favorable for development.  After the next few days, wind shear should increase substantially and be the demise of whatever this becomes by then.  The track forecasts in model guidance generally turn it north by the time it reaches 50-55°W.

And finally, 1200 miles east-southeast of Invest 98L is a new African easterly wave.  It's also battling a hostile environment and has pretty minimal chances of development in the coming week, but we'll want to watch it.  So, even though the map looks extremely active overall, only a couple of the disturbances could end up as named tropical storms.

It's too soon to know if any of these will become tropical storms, or in what order, but the next few names on this year's list are Emily, Franklin, Gert, Harold, and Idalia.  Harold and Idalia are new names on this list, replacing Harvey and Irma from six years ago.  Relative to the 1991-2020 climatology, this year's Accumulated Cyclone Energy (ACE) just crossed below the average today for the first time all season.

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