[Tropical] Tropical Cyclone Discussion

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WTNT41 KNHC 032044
TCDAT1

Tropical Storm Earl Discussion Number   4
NWS National Hurricane Center Miami FL       AL062022
500 PM AST Sat Sep 03 2022

Earl has strengthened this afternoon. Satellite data indicate the
previously exposed low-level center of the cyclone has been drawn
underneath an area of deep convection, with cloud top temperatures
colder than -70C. An Air Force Hurricane Hunter aircraft that
recently investigated the storm reported max flight-level (925 mb)
winds of 56 kt. This would support surface winds between 40 and 45
kt using a standard reduction factor. Based on these data, the
cyclone's improved satellite structure, and falling surface
pressures throughout the day, the initial intensity of Earl is
raised to 45 kt for this advisory.

The cyclone has strengthened some today despite facing moderate
deep-layer southwesterly shear. The shear is forecast to persist or
even increase during the next couple of days, so some fluctuation in
intensity is possible if the deep convection gets stripped away and
the center becomes exposed again. But, sea-surface temperatures
greater than 29C should continue to support convective development,
and the overall trend in the latest intensity guidance favors at
least slow strengthening into early next week. Then, the models
suggest that favorable interaction with an upper-level trough over
the warm waters of the western Atlantic will promote additional
strengthening, along with a broadening of the wind field. The latest
NHC intensity forecast has been raised closer to the HCCA and IVCN
consensus aids, and it now brings Earl up to hurricane strength at
days 4-5.

The initial motion of Earl is west-northwestward, or 290/9 kt. The
general forecast track reasoning has not changed. Earl is expected
to slow down as it moves west-northwestward to northwestward over
the next couple of days. A weakness in the subtropical ridge should
allow the cyclone to gradually turn northward early next week, then
move northeastward as it becomes steered by a mid- to upper-level
trough over the western Atlantic. The official NHC forecast track is
very similar to the previous forecast and lies slightly to the left
of the HCCA and TVCA aids.

Tropical-storm-force winds are still forecast to remain on the
northern and eastern side of the circulation, and are not expected
to move across the northern Leeward Islands, the Virgin Islands, or
Puerto Rico.  However, gusty winds in squalls are possible at these
locations through Sunday.


KEY MESSAGES:

1.  Heavy rainfall from Earl is expected to lead to limited flash,
urban, and small stream flooding impacts over the Leeward Islands,
U.S. and British Virgin Islands, and Puerto Rico this weekend. Rapid
rises on rivers and mudslides in areas of steep terrain are possible
in Puerto Rico.

2.  Earl is forecast to pass to the north of the the Virgin Islands
and Puerto Rico tonight and Sunday. Gusty winds, especially in
squalls, area possible on those islands through Sunday.


FORECAST POSITIONS AND MAX WINDS

INIT  03/2100Z 19.3N  63.2W   45 KT  50 MPH
 12H  04/0600Z 19.7N  64.3W   45 KT  50 MPH
 24H  04/1800Z 20.5N  65.4W   50 KT  60 MPH
 36H  05/0600Z 21.3N  66.0W   50 KT  60 MPH
 48H  05/1800Z 22.2N  66.4W   55 KT  65 MPH
 60H  06/0600Z 23.0N  66.6W   55 KT  65 MPH
 72H  06/1800Z 24.1N  66.6W   60 KT  70 MPH
 96H  07/1800Z 25.6N  65.6W   65 KT  75 MPH
120H  08/1800Z 27.7N  63.7W   75 KT  85 MPH

$$
Forecaster Reinhart
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