Atlantic Basin Tropical Cyclones

Tropical Storm Peter Forecast Discussion


098 
WTNT41 KNHC 211457
TCDAT1

Tropical Storm Peter Discussion Number  12
NWS National Hurricane Center Miami FL       AL162021
1100 AM AST Tue Sep 21 2021

Like the last several days, this morning's visible satellite
imagery indicates that Peter has become increasingly detached
from the remaining fragmented convection that is firing more than
100 n mi east of the center. An Air Force Reserve Reconnaissance
aircraft has been sampling the storm this morning and so far has
yet to find any flight level (925 mb) or SFMR winds above tropical
storm force, although they weren't able to fly the full pattern in
the northeastern quadrant. The initial intensity has been lowered
to 35 kt for this advisory, though the data so far suggests this
estimate is generous.

After taking a jog to the west overnight, Peter appears to have
resumed a slower west-northwest motion at 290/8 kt. Over the next
several days, Peter is expected to continue to slow down as it
gradually turns to the north and then north-northeast as a
deep-layer cyclone to the north is forecast to create a weakness in
the current low-level ridging. The track guidance is in general
agreement with this scenario, but differences remain in how sharp
this rightward turn will be. The latest NHC track forecast has
elected to stay close to the track consensus models TVCN and HCCA,
and is a bit right of the previous track.

After holding its own against a fairly hostile upper-level wind
environment during the last 24-48 hours, Peter appears to finally
be succumbing to the combination of 25-30 kt of deep-layer vertical
wind shear helping to import sub-50 percent mid-level relative
humidity over the center. This shear is not forecast to abate for
the next 36-48 hours, and it now appears likely Peter will not be
able to survive this unfavorable environment. The latest NHC
intensity forecast now weakens Peter to a tropical depression in 12
hours, and degenerates it to a remnant low in 48 hours. However,
given the current fragile state of the low-level circulation, it is
distinctly possible that Peter may open up into a trough even sooner
in the next 24-48 hours.


Key Messages:

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


FORECAST POSITIONS AND MAX WINDS

INIT  21/1500Z 19.9N  64.7W   35 KT  40 MPH
 12H  22/0000Z 20.7N  65.7W   30 KT  35 MPH
 24H  22/1200Z 21.7N  67.0W   30 KT  35 MPH
 36H  23/0000Z 22.7N  67.5W   25 KT  30 MPH
 48H  23/1200Z 23.4N  67.6W   25 KT  30 MPH...POST-TROP/REMNT LOW
 60H  24/0000Z 24.4N  67.0W   25 KT  30 MPH...POST-TROP/REMNT LOW
 72H  24/1200Z 25.4N  66.2W   25 KT  30 MPH...POST-TROP/REMNT LOW
 96H  25/1200Z 27.5N  64.4W   25 KT  30 MPH...POST-TROP/REMNT LOW
120H  26/1200Z 29.8N  62.5W   25 KT  30 MPH...POST-TROP/REMNT LOW

$$
Forecaster Papin




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