Tropical Storm Philippe Forecast Discussion Number 23

By | September 29, 2023

WTNT42 KNHC 290247

Tropical Storm Philippe Discussion Number  23
NWS National Hurricane Center Miami FL       AL172023
1100 PM AST Thu Sep 28 2023

There has not been much change in Philippe's organization this
evening with deep convection pulsing around the eastern and 
southern portions of the circulation.  Satellite imagery and a very 
recently arriving ASCAT pass indicate that the circulation is 
quite elongated east to west. In fact, the ASCAT data suggests 
Philippe likely lacks a well-defined center, but there are some 
indications that a center may be trying to re-form farther east. 
Subjective Dvorak T-numbers from SAB and TAFB were T2.0 (30 kt) and 
T2.5 (35 kt), respectively at 00Z, but the recently arriving ASCAT 
data revealed winds of around 35-36 kt. Given the typical 
undersampling of that instrument, the initial wind speed is held 
at 40 kt. 

The scatterometer data suggests that Philippe is located a little 
south of the previous estimates, but the storm appears to have moved 
little since the previous advisory. The track forecast is still 
quite challenging due to the current disorganized structure and the 
close proximity of Tropical Storm Rina to Philippe's east. The 
dynamical model guidance suggests that the cyclone will move slowly 
southwestward as Rina moves to the northeast of Philippe during the 
next two to three days.  By early next week, the storm is forecast 
to begin moving northward between a mid-level ridge over the 
east-central Atlantic and a mid- to upper-level trough over the 
southwestern Atlantic.  There is still significant spread in the 
models on where Philippe makes the northward turn, but the guidance 
is in slightly better agreement than 24 hours ago.  The updated NHC 
track is a little to the right of the previous forecast, but it 
lies a little west of the latest consensus aids. There continues to 
be larger-than-normal uncertainty in the latter portion of the 
track forecast.

Westerly shear, dry air, and Philippe's close proximity to Rina
have continued to prevent any increase in organization today.
Those negative environmental factors are expected to linger during
the next day or so, and little overall change in strength is
forecast during that time. Although not explicitly shown in this
forecast or by most of the model guidance, it is possible that
Philippe's circulation becomes increasing elongated and the system
dissipates within the next couple of days.  However, most of the 
guidance shows Philippe surviving, and then finding a more favorable
environment in which to strengthen early next week.  The NHC
intensity forecast has been nudged upward from 72-120 h, but it
remains below much the latest dynamical guidance and the consensus
aids.  Until there is a bit more clarity it seems prudent to stay
on the more conservative side of the guidance. As with the track
forecast, there is still significant uncertainty in the long-range
intensity prediction for Philippe.


INIT  29/0300Z 18.3N  55.0W   40 KT  45 MPH
 12H  29/1200Z 18.2N  55.2W   40 KT  45 MPH
 24H  30/0000Z 17.9N  55.6W   40 KT  45 MPH
 36H  30/1200Z 17.6N  55.9W   40 KT  45 MPH
 48H  01/0000Z 17.2N  56.2W   45 KT  50 MPH
 60H  01/1200Z 17.0N  56.6W   45 KT  50 MPH
 72H  02/0000Z 17.0N  57.0W   50 KT  60 MPH
 96H  03/0000Z 18.8N  57.6W   50 KT  60 MPH
120H  04/0000Z 21.7N  58.3W   50 KT  60 MPH

Forecaster Brown

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