Tropical Storm Philippe Forecast Discussion Number 29

By | September 30, 2023

WTNT42 KNHC 301455

Tropical Storm Philippe Discussion Number  29
NWS National Hurricane Center Miami FL       AL172023
1100 AM AST Sat Sep 30 2023

The satellite presentation of Philippe has not changed much this 
morning. The partially exposed low-level circulation lies on the 
western edge of a deep convective mass, as northwesterly shear 
continues to affect the storm's stucture. Recent UW-CIMSS objective 
estimates and subjective Dvorak classifications from TAFB and SAB 
have generally held steady, and so the initial intensity remains at 
45 kt for this advisory. The Air Force Reserve Hurricane Hunters 
are scheduled to investigate the system later today. 

The estimated initial motion of Philippe is southwestward (210/4 
kt). Philippe is not expected to move much during the next 12-24 h, 
although there is uncertainty even in the near term related to the 
extent of the interaction between Philippe and Tropical Storm Rina 
to its northeast. Most of the models show a slow and generally 
westward motion during the next day or so, which is reflected in 
the NHC forecast. Then, model spread increases regarding the timing 
of Philippe's turn toward the northwest and north early next week. 
Stronger model solutions (GFS, HAFS-A) depict an earlier turn along 
the eastern side of the guidance envelope, while weaker models 
(ECMWF, UKMET) show the storm making it west of 60W before turning. 
Given the greater-than-normal model spread, the NHC forecast remains 
near the TVCA and HCCA aids for this portion of the forecast, with 
a slight westward adjustment from the previous prediction. By days 
4-5, Philippe is forecast to move faster toward the north and 
northeast between a mid-level ridge over the central Atlantic and a 
deep-layer trough over the western Atlantic.  

Given the sheared structure of Philippe, only minor intensity 
fluctuations are expected during the next 12-24 h. Thereafter, the 
shear is generally forecast to decrease on Monday and Tuesday, 
although the magnitude remains at least somewhat dependent on how 
far west Philippe tracks. Based on our latest track forecast, it is 
assumed that the shear will relax enough to be conducive for some 
strengthening over the 29-29.5C SSTs, and this prediction shows 
Philippe becoming a hurricane by 60 h. Overall, the environment 
appears reasonably favorable for continued strengthening through 
days 4-5 as the cyclone moves into the subtropical Atlantic. The  
updated intensity forecast has been raised during this period to 
show additional strengthening, although it still lies below the 
IVCN and HCCA aids, so further adjustments could be necessary. 


INIT  30/1500Z 16.9N  56.3W   45 KT  50 MPH
 12H  01/0000Z 16.8N  56.6W   50 KT  60 MPH
 24H  01/1200Z 17.0N  57.2W   50 KT  60 MPH
 36H  02/0000Z 17.6N  58.0W   55 KT  65 MPH
 48H  02/1200Z 18.5N  58.9W   60 KT  70 MPH
 60H  03/0000Z 19.7N  59.6W   65 KT  75 MPH
 72H  03/1200Z 21.0N  59.9W   70 KT  80 MPH
 96H  04/1200Z 24.9N  59.3W   75 KT  85 MPH
120H  05/1200Z 28.5N  57.0W   75 KT  85 MPH

Forecaster Reinhart

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