[Tropical] Tropical Cyclone Discussion

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WTNT41 KNHC 030236
TCDAT1

Tropical Storm Earl Discussion Number   1
NWS National Hurricane Center Miami FL       AL062022
1100 PM AST Fri Sep 02 2022

Air Force Reserve and NOAA Hurricane Hunter aircraft each flew
missions into the area of low pressure east of the Leeward Islands
this afternoon into this evening, and the data from those flights
indicated that the circulation and center of the low became well
defined today.  Deep convection has also persisted with the low,
albeit sheared near and to the east of the center, which means the
system has finally met the criteria of a tropical cyclone.
Flight-level, surface, and dropsonde data from the reconnaissance
flights all indicate that the system is producing
tropical-storm-force winds in the convection well to the east of the
center, and for good measure TAFB provided a Dvorak estimate of
T2.5/35 kt.  The low is therefore being designated as Tropical Storm
Earl with maximum winds of 35 kt.  The minimum pressure is estimated
to be 1005 mb based on an Air Force dropsonde that measured a
surface pressure of 1007 mb with 23-kt winds.

Earl is moving toward the west-northwest, or 295/12 kt.  The track
guidance is in fairly good agreement during the next 3 days, with a
low- to mid-level ridge expected to steer Earl west-northwestward
and then northwestward at decreasing forward speed.  The ridge to
the north is forecast to weaken and shift westward around day 3,
which should cause Earl to slow down to less than 5 kt and turn
northward by day 4, and then north-northeastward by day 5 as it
begins to feel the influence of the mid-latitude westerlies to the
north.  The biggest outliers on days 4 and 5 are the GFS and HMON,
which show a stronger Earl moving faster toward the northeast.  For
now, the NHC official forecast favors a slower scenario on days 4
and 5, closer to the ECMWF, HWRF, HCCA, and TVCN.

Moderate to strong shear is likely to continue affecting Earl for
much of the next 5 days, possibly peaking in 3 to 4 days according
to the SHIPS guidance.  Mid-level relative humidity ahead of the
system also remains lower than what is ideal for strengthening, and
as a result, the NHC intensity forecast shows only modest
intensification through the forecast period.  This forecast is very
close to the IVCN and HCCA consensus aids.

Tropical-storm-force winds are forecast to remain on the northern
and eastern side of the circulation, and as a result, are not
expected to move across the northern Leeward Islands, the Virgin
Islands, or Puerto Rico.  However, any southward shift of Earl's
center would increase the risk of tropical-storm-force winds in
those areas.


KEY MESSAGES:

1.  Tropical storm Earl is forecast to pass near or just to the
north of the northern Leeward Islands, the Virgin Islands, and
Puerto Rico over the weekend.  Gusty winds, especially in squalls,
area possible on those islands over the next day or two.

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


FORECAST POSITIONS AND MAX WINDS

INIT  03/0300Z 18.4N  60.3W   35 KT  40 MPH
 12H  03/1200Z 18.9N  62.0W   35 KT  40 MPH
 24H  04/0000Z 19.5N  63.8W   40 KT  45 MPH
 36H  04/1200Z 20.2N  65.3W   40 KT  45 MPH
 48H  05/0000Z 20.9N  66.4W   40 KT  45 MPH
 60H  05/1200Z 21.5N  67.2W   40 KT  45 MPH
 72H  06/0000Z 22.2N  67.7W   40 KT  45 MPH
 96H  07/0000Z 23.3N  67.8W   40 KT  45 MPH
120H  08/0000Z 24.7N  67.0W   45 KT  50 MPH

$$
Forecaster Berg
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