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Tropical Storm Peter Forecast Discussion

WTNT41 KNHC 202032

Tropical Storm Peter Discussion Number   9
NWS National Hurricane Center Miami FL       AL162021
500 PM AST Mon Sep 20 2021

Peter's evolution on satellite today is nearly a repeat of 
yesterday, with the deep convection having been stripped well east 
of the center in the morning and then redeveloping over and east of 
the center by the afternoon. An Air Force Reserve Hurricane Hunter 
aircraft investigating Peter this morning and early afternoon 
provided data during a few different passes through the northeast 
quadrant that supported peak surface winds of 40-45 kt. Since the 
convection has returned it is reasonable to assume that no weakening 
has occurred since the aircraft departed the cyclone, and the 
initial advisory intensity remains 45 kt.

Vertical wind shear is forecast to remain near 30 kt for the next 
few days as Peter interacts with an upper trough to its west, so 
some weakening is anticipated during that time. By late in the 
forecast period, the shear should lessen somewhat as the cyclone 
lifts north of the upper trough. Therefore, slow strengthening is 
indicated by late this week. There remains a possibility that Peter 
does not survive the shear over the next few days. However, the 
storm thus far has shown some resiliency to the hostile environment. 
The latest NHC intensity forecast is little changed from the 
previous one and remains near the various intensity consensus 

Peter continues to move west-northwest but at a slightly slower pace 
of around 12 kt. The forecast track reasoning for the cyclone 
remains the same. The west-northwestward motion is forecast to 
continue for the next two days as the system remains to the 
southwest of a subtropical ridge. By Wednesday, Peter should slow 
down and turn northwest then north as it reaches a developing 
weakness in the ridge carved out by a mid-latitude trough moving 
across the northeastern United States. There were no significant 
changes to the track or the track guidance from the previous 
advisory, and the latest NHC track is closest to the TVCN and GFEX 
consensus tracks. 

Based on the latest track, intensity, and wind radii forecasts, no
tropical storm watches or warnings are required for the northern
Leeward Islands, Virgin Islands, or Puerto Rico at this time.
However, locally heavy rain is possible today and Tuesday when
Peter is expected to pass to the north of these locations.

Key Messages:

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


INIT  20/2100Z 20.0N  61.8W   45 KT  50 MPH
 12H  21/0600Z 20.6N  63.5W   45 KT  50 MPH
 24H  21/1800Z 21.4N  65.4W   40 KT  45 MPH
 36H  22/0600Z 22.2N  66.9W   40 KT  45 MPH
 48H  22/1800Z 23.1N  68.0W   35 KT  40 MPH
 60H  23/0600Z 24.0N  68.3W   35 KT  40 MPH
 72H  23/1800Z 25.1N  68.0W   30 KT  35 MPH
 96H  24/1800Z 27.8N  66.9W   30 KT  35 MPH
120H  25/1800Z 30.5N  65.8W   35 KT  40 MPH

Forecaster Latto

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