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Tropical Storm PETER

Tropical Storm Peter Discussion Number   5
NWS National Hurricane Center Miami FL       AL162021
500 PM AST Sun Sep 19 2021
Over the past few hours deep convection with cloud tops as cold as
-85 degrees C have developed near and to the east of the center of
Peter. An Air Force Reserve Hurricane Hunter aircraft investigating
the system earlier provided data during several legs of the flight
that confirmed an intensity of 40 kt. A blend of the latest Dvorak
T- and CI- numbers from TAFB are consistent with that data, and
therefore the initial intensity remains 40 kt for this advisory.
The vertical wind shear that stripped Peter of its deep convection 
earlier today is forecast to increase further through tonight and 
persist for at least a few days. Global model simulated satellite 
imagery suggests this latest burst of convection will also become 
removed from the center within several hours, with the cyclone 
struggling to maintain persistent deep convection throughout much of 
the 5-day forecast period. Therefore, despite being over very warm 
waters, Peter is forecast to slowly weaken over the next several 
days. The intensity model guidance is in decent agreement on this 
scenario, and the NHC forecast remains near the various intensity 
consensus solutions. As mentioned in the previous discussion, there 
are some indications, particularly by the GFS, that Peter could open 
back into a wave within a few days which adds some additional 
uncertainty to the intensity forecast.
Peter's initial motion remains 290/15 kt. The storm is forecast to 
continue to move in this west-northwestward direction for the next 
couple of days as it is steered to the south of a subtropical ridge. 
This ridge is expected to weaken in a few days which should cause 
the cyclone to slow its forward motion and turn northwestward. Late 
in the forecast period a turn to the north and possibly northeast 
is expected to occur as Peter gets caught in the flow around a 
large trough to its north. The model guidance has shifted westward 
beyond day 2, in part due to a faster forward motion. While the 
timing of the cyclone's turn to the north remains the same, the NHC 
forecast was shifted to the left beyond 48 h, but still remains to 
the east of the consensus.
Based on the track, intensity, and wind radii forecast, no tropical
storm watches or warnings are required for the northern Leeward
Islands, Virgin Islands or Puerto Rico.  However, interests there
should monitor the progress of the system as locally heavy rain is
possible on Monday and Tuesday when it is expected to pass to the
north of the area.
Key Messages:
1. Rainfall around the southern periphery of Tropical Storm Peter
may lead to areas of urban and small stream flooding from late today
into Tuesday across Puerto Rico, the Virgin Islands, and the
Northern Leeward Islands.
INIT  19/2100Z 18.4N  57.8W   40 KT  45 MPH
 12H  20/0600Z 19.1N  59.8W   40 KT  45 MPH
 24H  20/1800Z 19.9N  62.1W   35 KT  40 MPH
 36H  21/0600Z 20.8N  64.3W   35 KT  40 MPH
 48H  21/1800Z 21.9N  66.0W   35 KT  40 MPH
 60H  22/0600Z 22.9N  67.2W   35 KT  40 MPH
 72H  22/1800Z 24.1N  68.2W   30 KT  35 MPH
 96H  23/1800Z 26.1N  68.3W   30 KT  35 MPH
120H  24/1800Z 27.7N  67.5W   30 KT  35 MPH
Forecaster Latto