Official Discussion issued by the National Hurricane Center

Philippe (AL172023) DATA RELEASED: 9/24/2023 3:00:00 PM UTC

Copy of official data

Tropical Storm Philippe Discussion Number   5
NWS National Hurricane Center Miami FL       AL172023
1100 AM AST Sun Sep 24 2023

Philippe is a challenging tropical cyclone to analyze this morning. 
On one hand, the overall satellite presentation has improved since 
yesterday, and a 0907Z SSMIS microwave pass shows a possible 
mid-level eye.  Yet the 1-min GOES16 imagery reveals a weak 
low-level swirl southwest of the main convective blob, and ASCAT-B 
near 12Z showed a disorganized inner core with less wind than one 
might expect (albeit very contaminated with rain).  Overall, 
intensity estimates have risen since the last advisory, so the 
initial wind speed is set to 45 kt, similar to the TAFB/SAB values, 
but this should be considered fairly uncertain.

Little change in intensity is forecast with the storm during the 
next couple of days as increasing shear is forecast to otherwise 
counteract a conducive environment.  There are a variety of 
solutions after that point, with some models showing a stronger 
Philippe after finding a lower-shear environment, while others 
suggesting that the storm succumbs to the shear from an 
upper-level trough.  There are no easy answers here with moderate 
shear cases in high SST/moisture conditions well known to have 
higher errors due to an inherent lack of predictability.  The new 
forecast splits the difference in the model guidance, lying near 
the consensus and the previous forecast, and we will just have to 
see if a trend emerges for the eventual intensity of Philippe.

The long-term motion of the storm is westward or 280/10 kt. The 
subtropical ridge to the north of Philippe is forecast to gradually 
weaken and slide eastward in a day or two, allowing the tropical 
storm to move more west-northwestward and northwestward by the 
middle of the week.  Uncertainty grows after that point, with the 
track seemingly dependent on the intensity.  A stronger system 
would probably turn northward, like the GFS/HWRF/HMON models, while 
a weaker one, like the UKMET/ECMWF solutions, would take a left 
turn under the low-level subtropical ridge.  For now, little change 
was made to the long-range forecast given all of the uncertainty.


INIT  24/1500Z 16.2N  41.7W   45 KT  50 MPH
12H  25/0000Z 16.5N  43.3W   45 KT  50 MPH
24H  25/1200Z 16.9N  45.6W   45 KT  50 MPH
36H  26/0000Z 17.4N  47.8W   45 KT  50 MPH
48H  26/1200Z 18.0N  49.7W   45 KT  50 MPH
60H  27/0000Z 18.9N  51.0W   50 KT  60 MPH
72H  27/1200Z 20.0N  52.5W   50 KT  60 MPH
96H  28/1200Z 22.5N  54.5W   55 KT  65 MPH
120H  29/1200Z 24.0N  55.5W   55 KT  65 MPH

Forecaster Blake