[Tropical] Tropical Cyclone Discussion

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WTNT42 KNHC 290247
TCDAT2

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.


FORECAST POSITIONS AND MAX WINDS

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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