23 September 2019

Jerry heading for Bermuda, Karen heading for Puerto Rico, soon-to-be Lorenzo near Cabo Verde

The tropical Atlantic continues to bubble with activity, and there could be three named storms by the end of the day.
Tropical Storm Jerry is centered about 350 miles southwest of Bermuda and is forecast to pass just north of (or over) the island on Wednesday as a tropical storm -- about 6.5 days after Category 3 Hurricane Humberto passed north of the island. It is forecast to continue to weaken in the face of wind shear, dry air, and cooler ocean temperatures, but tropical storm conditions should reach Bermuda on Tuesday evening. Beyond the Bermuda encounter, Jerry will dissipate over the cold north-central Atlantic later in the week.
Next on the list is Tropical Storm Karen, which formed on Sunday from a tropical wave near Trinidad and Tobago. It has since entered the far eastern Caribbean and is battling moderate vertical wind shear (it looks like it's losing that battle). The forecast brings it north, and tropical storm warnings are in effect for Puerto Rico and the Virgin Islands.  It's not even a given that it remains intact that long, as some models dissipate it before then.
But, assuming that it holds together, models are in good agreement on a northward track for another 1-2 days after crossing Puerto Rico on Tuesday.  At that point, a strong ridge of high pressure is forecast to build to its north, which would force it to make a sharp left turn to the west.  The ridge is pretty robust in the models, so a continued westward track would bring it toward the Bahamas, Florida, and/or the southeast US coast in about one week.

Track density from the 23Sep 00Z ECMWF 50-member ensemble. The 00Z deterministic run is shown by the cyan dashed line, and the 5-day NHC forecast is the black solid line. (UAlbany)
But that all comes with the uncertainty built into the survival of the tropical cyclone in the next couple of days, the exact strength and position of the ridge, and a list of environmental factors that Karen will need to contend with beyond two days.  At this long lead time, it's just worth being aware of this "left turn" possibility, and knowing that the global models and their ensembles have supported this scenario for a couple days now.

Finally, Tropical Depression 13 is located south of the Cabo Verde islands and is very close to becoming the 12th named storm of the season: Lorenzo.  Models are in excellent agreement on this becoming a strong hurricane in a few days, and on a turn to the north before reaching 60°W.  It appears at this time that it will never be a threat to land.  The NHC forecast brings this close to major hurricane status on Saturday as it begins the northward turn.

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