07 September 2020

Two new tropical depressions form

Finally, from a mess of scattered easterly waves in the deep tropics that people have been watching for days, two tropical cyclones have emerged: Tropical Depressions 17 and 18.  Both are located in the far eastern Atlantic, and both are likely to become tropical storms soon. The next two names on the list are Paulette and Rene -- and the record earliest dates for 16th and 17th named storm formation are September 17 and 18 (Philippe and Rita in 2005).

TD17 is the western one, and faces a more hostile environment in the coming days. While it could easily become a tropical storm, there is no model guidance that even remotely suggests it could become a hurricane.  It looks likely that it will make a turn toward the northwest in 5-6 days.

TD18 is still east of Cabo Verde, where a tropical storm warning is in effect.  Storms can and do form between the African coast and Cabo Verde, but it's impressively quick (recall that Fred passed over the islands as a hurricane in 2015!). This one does have several models that bring it up to hurricane -- and even major hurricane -- intensity in a few days. It looks like it will turn safely to the north well before becoming a concern to land, but that will depend on the strength of the subtropical ridge to its north, which has had notable breaks in it lately.

If these don't start cranking out of ACE (Accumulated Cyclone Energy) real soon, then for the first time this year, the Atlantic hurricane season will be "average" -- in terms of ACE. As of this writing, 2020 is at 45.0, and the average (over the past fifty years) through today is 42.6. We cross below average on the 9th if nothing else happens. But the odds are good that TD 17 and/or 18 will be TS Paulette and Rene by then and delay that crossing a bit.

And while 2020 is smashing records for the earliest date of the Nth named storm formation, it really does look quite average when compared to historical values of ACE through today.

Aside from TD 17 and 18, there are two other areas of interest coming up this week: another easterly wave exiting the African coast, and a weak low pressure system near Bermuda that is drifting toward the U.S. mid-Atlantic coast.  NHC is giving both of these just a 30% probability of becoming at least a tropical depression within the next five days.

I was also reminded of a unique moment that occurred three (and ten) years ago today. In the anxiety and haste of preparing for Hurricane Irma's potential arrival on September 10th, 2017, I was struck by the satellite presentation on the morning of the 7th and knew it reminded me of something. And it did... I remembered the same set and placement of active named storms just a few years prior (K, I, J in 2010) and made this comparison image that I shared on Twitter: https://twitter.com/BMcNoldy/status/905770545899286528

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