Atlantic Hurricane and Tropical Cyclone Track Updates

Tropical Depression Peter Forecast Discussion

WTNT41 KNHC 220244

Tropical Depression Peter Discussion Number  14
NWS National Hurricane Center Miami FL       AL162021
1100 PM AST Tue Sep 21 2021

The last visible satellite images of Peter this evening indicated 
that its low-level center was losing definition and becoming even 
more elongated. Earlier, new bursts of convection associated with 
Peter had become oriented along a northeast to southwest axis, a 
possible sign that Peter may no longer have a well-defined center 
and could be opening up into a trough. But the estimated center 
position is now obscured by convective debris, and without recent 
scatterometer data to prove otherwise, Peter is maintained as a 
sheared tropical depression for this advisory. The initial intensity 
of 30 kt is consistent with a UW-CIMSS ADT objective 30-kt estimate 
and a T2.0/30 kt Dvorak classification from SAB.

It is estimated that Peter is moving northwestward, or 310/6 kt, 
although this is somewhat uncertain given the degraded low-level 
structure of the cyclone. The track reasoning remains consistent 
with previous advisories. Peter is forecast to turn more northward 
on Wednesday, and then move north-northeastward to northeastward 
through the end of the week as a trough to the north and northeast 
of Peter erodes the southern portion of the low-level steering 
ridge. The track consensus aids have shifted slightly to the right 
this cycle, and so the latest NHC track forecast has been adjusted a 
little to the right of the previous one.

Environmental conditions are expected to remain hostile for Peter 
over the next couple of days. Strong vertical wind shear of 25-30 kt 
will persist for the next 24-36 h, and GFS and ECMWF model simulated 
satellite imagery suggest that Peter will be unable to sustain 
enough deep, organized convection to maintain its status as a 
tropical cyclone for much longer. Thus, the NHC forecast shows Peter 
becoming a remnant low in 36 h, with some additional weakening 
expected before dissipation by this weekend. Of course, without 
sufficient convection to sustain the low-level vortex, it would not 
be surprising if the depression degenerated into a trough even 
sooner than forecast.

Key Messages:

1. Rainfall around the southern periphery of Peter may lead to areas 
of urban and small stream flooding through early Wednesday across 
northern Hispaniola, Puerto Rico, and portions of the Virgin 


INIT  22/0300Z 20.8N  65.3W   30 KT  35 MPH
 12H  22/1200Z 21.6N  66.2W   30 KT  35 MPH
 24H  23/0000Z 22.6N  66.8W   25 KT  30 MPH
 36H  23/1200Z 23.6N  66.7W   25 KT  30 MPH...POST-TROP/REMNT LOW
 48H  24/0000Z 24.6N  66.0W   25 KT  30 MPH...POST-TROP/REMNT LOW
 60H  24/1200Z 25.7N  65.1W   25 KT  30 MPH...POST-TROP/REMNT LOW
 72H  25/0000Z...DISSIPATED

Forecaster Reinhart

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