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Tropical Storm Philippe Discussion Number  28
NWS National Hurricane Center Miami FL       AL172023
500 AM AST Sat Sep 30 2023
 
An Air Force Reserve Hurricane Hunter crew investigated Philippe a 
few hours ago and found that the minimum pressure had fallen to 999 
mb, however the maximum winds do not appear to have increased.  The 
maximum flight-level wind was 46 kt at 700 mb, and SFMR readings 
outside of deep convection were as high as 45 kt (SFMR measurements 
higher than 50 kt appeared questionable due to coincident heavy 
rain).  The low-level center remains located on the northwestern 
edge of the deep convection due to continued shear.

The reconnaissance fixes showed that Philippe has been moving toward 
the south-southwest (200 degrees) at about 4 kt.  The storm has 
moved a little farther south than expected, possibly due to a more 
pronounced binary interaction with Tropical Storm Rina about 450 n 
mi to its east-northeast.  As the interaction continues, Philippe is 
forecast to move slowly toward the west and then northwest during 
the next few days.  However, there is still quite a bit of model 
spread in how far west Philippe will get before it turns, and the 
ECMWF and HAFS-B models in particularly bring the storm very close 
to the northern Leeward Islands in about 48 hours.  The NHC track 
forecast has been shifted west of the previous prediction and lies 
just to the west of the TVCA consensus aid.  It is noteworthy that 
several models and ensemble members still lie west of the new 
forecast, and it's possible that additional adjustments may be 
required in future forecast cycles.  All models show Philippe 
accelerating toward the north and north-northeast by days 4 and 5, 
steered by the flow between a mid-level high over the central 
Atlantic and a deep-layer trough over the western Atlantic.

The intensity forecast remains tricky and is complicated by 
competing positive and negative environmental factors.  On one hand, 
moderate-to-strong northwesterly shear is likely to continue at 
least for the next 48 hours.  However, the magnitude of the shear 
will depend on Philippe's exact location, and it could also be 
offset by a more diffluent upper-level environment.  Since the storm 
has already been overachieving in the sheared environment, the NHC 
intensity forecast shows gradual strengthening during the next few 
days, and is near or just below the IVCN and HCCA consensus aids 
through 60 hours.  The atmosphere could become more favorable for 
strengthening after that time, and the NHC forecast now shows 
Philippe reaching hurricane intensity while it recurves toward the 
subtropical Atlantic.  It's worth noting that this new forecast is 
still on the conservative side, and that many of the intensity 
models and consensus aids are at least 20 kt higher on days 4 and 5. 
 Only the ECMWF and its SHIPS and LGEM derivatives remain on the 
weaker end of the scale and don't bring Philippe to hurricane 
strength.
 
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  30/0900Z 17.1N  55.9W   45 KT  50 MPH
 12H  30/1800Z 16.9N  56.2W   50 KT  60 MPH
 24H  01/0600Z 16.9N  56.7W   50 KT  60 MPH
 36H  01/1800Z 17.3N  57.5W   55 KT  65 MPH
 48H  02/0600Z 18.0N  58.3W   60 KT  70 MPH
 60H  02/1800Z 19.2N  59.0W   65 KT  75 MPH
 72H  03/0600Z 20.7N  59.5W   65 KT  75 MPH
 96H  04/0600Z 24.1N  59.3W   65 KT  75 MPH
120H  05/0600Z 28.1N  56.6W   65 KT  75 MPH
 
$$
Forecaster Berg
 
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