Tropical Storm PETER Advisory mar, 21-09

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Tropical Storm Peter Discussion Number  11
NWS National Hurricane Center Miami FL       AL162021
500 AM AST Tue Sep 21 2021

Peter is a ragged and strongly sheared tropical storm.  Satellite
images and surface observations indicate that the low-level center
is fully exposed and located about 100 miles west-southwest of the
edge of the main area of deep convection.  This very asymmetric
structure is due to strong west-southwesterly shear associated with
an upper-level low to the northwest of Peter.  The initial intensity
is held at 45 kt based on the Dvorak CI-numbers from TAFB and SAB,
but this could be a little generous.  An Air Force Hurricane Hunter
aircraft is scheduled to investigate the storm later this morning.

Since the storm has decoupled, the low-level center has been moving
just south of due west at 265/10 kt.  This motion has brought the
storm to the southwest of the previous track.  The models insist
that Peter will turn back to the west-northwest soon and continue
moving in that direction during the next couple of days as the storm
moves in the flow on the southwest side of a mid-level ridge.  After
that time, a turn to the north and then northeast is expected as
Peter moves toward broad troughing over the north Atlantic.  The
latest run of the ECMWF has come into line with the remainder of the
guidance, and the new forecast is to the west of, and slower than,
the previous one.  This prediction lies on the south side of the
guidance envelope during the first 24 hours of the forecast.

Peter is expected to remain in fairly hostile conditions during the
next few days with strong westerly shear continuing and dry air
likely entraining into the circulation.  These negative factors for
the storm should cause a slow decay, and that is reflected in the
NHC forecast.  In fact, some of the guidance suggests that Peter
could succumb to the hostile conditions and open into a trough later
this week.  The NHC intensity forecast is the same as the previous
one and in line with the majority of the guidance.

Key Messages:

1. Rainfall around the southern periphery of Tropical Storm Peter
could lead to areas of urban and small stream flooding through
Tuesday across northern Hispaniola, Puerto Rico, portions of the
Virgin Islands, and the Northern Leeward Islands.


FORECAST POSITIONS AND MAX WINDS

INIT  21/0900Z 19.6N  63.8W   45 KT  50 MPH
 12H  21/1800Z 20.3N  65.3W   40 KT  45 MPH
 24H  22/0600Z 21.2N  66.9W   40 KT  45 MPH
 36H  22/1800Z 22.2N  67.9W   35 KT  40 MPH
 48H  23/0600Z 23.2N  68.2W   35 KT  40 MPH
 60H  23/1800Z 24.0N  68.0W   30 KT  35 MPH
 72H  24/0600Z 25.2N  67.2W   30 KT  35 MPH
 96H  25/0600Z 27.2N  65.8W   30 KT  35 MPH
120H  26/0600Z 29.2N  64.2W   30 KT  35 MPH

$$
Forecaster Cangialosi