Tropical Storm Philippe Forecast Discussion Number 31

By | October 1, 2023

WTNT42 KNHC 010245

Tropical Storm Philippe Discussion Number  31
NWS National Hurricane Center Miami FL       AL172023
1100 PM AST Sat Sep 30 2023

Philippe's convective cloud pattern remains rather ragged-looking,
but there are very cold cloud tops of -80 deg C or colder over the
southeastern part of the circulation.  The center of circulation is
estimated to be near the northwestern edge of the main area of deep
convection.  There is little evidence of banding features at this
time.  The current intensity estimate is kept at 45 kt in agreement 
with the latest Dvorak classification from TAFB although objective 
satellite estimates are somewhat lower.  A recent scatterometer 
pass showed slightly higher winds over the southeastern quadrant 
but these are believed to be rain-inflated.  Another Hurricane 
Hunter aircraft is scheduled to investigate Philippe tomorrow 
morning to check on the intensity of the storm.

The motion is somewhat uncertain since the center is not easy to
locate in nighttime satellite imagery.  However it appears that
Philippe is moving more to the right and the initial motion
estimate is now 230/4 kt.  Steering currents are expected to remain 
ill-defined for the next day or two, but a weak mid-level high to 
the northeast of the system should cause Philippe to turn 
northwestward on Sunday.  In about 3 days, a turn to the north is 
expected as the cyclone moves along the western side of the high.  
Late in the forecast period, the system should turn toward the 
north-northeast on the southeast side of a mid-tropospheric trough 
over the western Atlantic.  The latest track guidance for the next 
48 hours or so, in particular the new GFS, has shifted westward 
from the previous cycle.  This has resulted in a westward shift of 
the model consensus and necessitated a westward shift in the NHC 
track as well, which is now closer to the northern Leeward Islands. 
It should be noted that the model guidance continues to show very 
little outward extent of tropical-storm-force winds over the 
western semicircle of Philippe through 48 hours, and this forecast 
still does not necessitate the issuance of tropical storm watches 
for those islands.  However, interests there should continue to 
monitor the progress of Philippe.

Based on the global model forecasts, the system is likely to
continue experiencing significant vertical wind shear for the next
day or two.  Therefore only a slow increase in intensity is
forecast during the next couple of days.  Later in the forecast 
period, vertical shear is expected to lessen somewhat which should 
allow the system to strengthen into a hurricane, as suggested by 
the regional hurricane model, HAFS-A.  However, the official 
intensity forecast is now above most of the model guidance.


INIT  01/0300Z 16.1N  57.0W   45 KT  50 MPH
 12H  01/1200Z 16.5N  57.7W   45 KT  50 MPH
 24H  02/0000Z 17.1N  58.6W   50 KT  60 MPH
 36H  02/1200Z 17.8N  59.4W   55 KT  65 MPH
 48H  03/0000Z 18.6N  60.3W   60 KT  70 MPH
 60H  03/1200Z 19.6N  61.0W   60 KT  70 MPH
 72H  04/0000Z 21.1N  61.2W   65 KT  75 MPH
 96H  05/0000Z 24.8N  61.1W   75 KT  85 MPH
120H  06/0000Z 28.5N  59.2W   80 KT  90 MPH

Forecaster Pasch

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