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WTNT42 KNHC 300835

TCDAT2

 

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