Official Discussion issued by the National Hurricane Center

Philippe (AL172023) DATA RELEASED: 9/29/2023 9:00:00 AM UTC

Copy of official data

Tropical Storm Philippe Discussion Number  24
NWS National Hurricane Center Miami FL       AL172023
500 AM AST Fri Sep 29 2023

A 0546 UTC GMI microwave pass showed that Philippe continues to 
have a broad circulation, with the low-level center located 
somewhere near the northwestern edge of a large area of deep 
convection.  There is a large range in the subjective Dvorak 
estimates (30-55 kt), but the various objective numbers from 
UW-CIMSS are in closer agreement (35-45 kt).  Using a blend of 
these values, as well as ASCAT data from last evening, Philippe's 
intensity is held at 40 kt.

While there is a bit of uncertainty in the exact location of the 
center, the storm does appear to be drifting toward the southwest 
(235 degrees) at about 2 kt.  Philippe's movement during the next 
3-4 days is likely to be dictated by binary interaction with 
Tropical Storm Rina to the east.  The bulk of the track guidance 
indicates that Philippe will dip farther toward the southwest during 
the next 48 hours due to Rina's influence, but then turn toward the 
northwest and north on days 3 through 5 as a mid-tropospheric high 
builds over the central Atlantic.  The new NHC track forecast is 
not much different from the previous prediction and is close to the 
TVCA and HCCA consensus aids.  The HAFS regional hurricane models 
show little to no interaction between Philippe and Rina during the 
next few days.  However, with the two storms located only 500 n mi 
apart from each other, some degree of interaction is likely, and 
therefore the western solutions shown by those models (near or over 
the northern Leeward Islands) appear to be outliers at this time.  
That said, there continues to be larger-than-normal uncertainty in 
Philippe's future track.

A combination of shear, dry air, and Philippe's proximity to Rina 
are likely to cause little change in intensity for the next day or 
so.  However, the global models have trended toward Philippe not 
only surviving the next few days, but also deepening in an 
environment of increasing upper-level divergence (and still over 
very warm waters of 29-30 degrees Celsius).  The NHC intensity 
forecast has been nudged upward from 36 hours onward, although it 
still sits well below most of the intensity models, including the 
consensus aids, during the latter part of the forecast period.  
Until it becomes more clear how Philippe will evolve over the next 
couple of days, the official intensity forecast will remain on the 
conservative side, but future adjustments to the forecast are 
becoming more likely.


INIT  29/0900Z 18.5N  55.2W   40 KT  45 MPH
12H  29/1800Z 18.3N  55.4W   40 KT  45 MPH
24H  30/0600Z 17.9N  55.7W   40 KT  45 MPH
36H  30/1800Z 17.4N  56.0W   45 KT  50 MPH
48H  01/0600Z 17.1N  56.4W   50 KT  60 MPH
60H  01/1800Z 17.1N  56.8W   50 KT  60 MPH
72H  02/0600Z 17.6N  57.2W   55 KT  65 MPH
96H  03/0600Z 20.0N  57.9W   55 KT  65 MPH
120H  04/0600Z 23.1N  58.1W   55 KT  65 MPH

Forecaster Berg