Official Discussion issued by the National Hurricane Center

Philippe (AL172023) DATA RELEASED: 9/25/2023 9:00:00 AM UTC

Copy of official data

Tropical Storm Philippe Discussion Number   8
NWS National Hurricane Center Miami FL       AL172023
500 AM AST Mon Sep 25 2023

The satellite appearance of Philippe has remained steady overnight. 
Burst of deep convection, with cold cloud tops to -80 C, continue 
from time to time within the overall convective plume. An AMSR 
microwave pass depicts that the convection remains displaced to the 
east of the low-level center, with the system still lacking 
organization. Philippe is struggling to become better organized due 
to the strong mid-level shear impacting the system. Subjective 
Dvorak intensity estimates from TAFB and SAB remain at T3.0/45-kt 
this cycle, and the initial intensity is held at 45 kt.

Philippe will continue to be in an environment with moderate to 
strong mid-level shear, which will limit the overall organization of 
the system. The storm is traversing fairly warm sea surface 
temperatures around 29C and favorable mid-level RH values the next 
few days. Given these mixed parameters and lack of organization, the 
NHC forecast calls for Philippe to remain fairly steady with the
potential for some slow strengthening by the end of the period. 
However, there remains uncertainty in the intensity forecast given 
the guidance envelope. The ECMWF suggest the system remains steady 
or may even weaken, while the GFS depicts strengthening with the 
system moving far enough north into a lower shear environment. The 
intensity forecast is similar to the previous, and is closest to the 
IVCN and HCCA consensus aids.

The system is moving west-northwest at an estimated motion of 285/9 
kt. Philippe should continue west-northwestward over the next day or 
two, steered along the southern side of a mid-level ridge. In about 
2 days, all models depict a weakness developing in the ridge, but 
the track guidance diverges quite drastically, and it is directly 
related to the intensity of the system. A deeper, stronger system, 
like the GFS depicts, will feel the weakness in the ridge and curve 
the system faster on a more northwestward track. However, a weaker, 
shallow cyclone, like the ECMWF depicts, will cause the system to 
continue on a west-northwestward or even westward track. The NHC 
track forecast continues to be in the middle of the guidance, and 
lies close to both the simple and corrected consensus aids. This 
remains a low confidence track and intensity forecast.


INIT  25/0900Z 17.4N  43.9W   45 KT  50 MPH
12H  25/1800Z 17.8N  45.7W   45 KT  50 MPH
24H  26/0600Z 18.3N  47.9W   45 KT  50 MPH
36H  26/1800Z 19.0N  49.9W   45 KT  50 MPH
48H  27/0600Z 20.0N  51.8W   45 KT  50 MPH
60H  27/1800Z 21.2N  53.3W   50 KT  60 MPH
72H  28/0600Z 22.4N  54.5W   50 KT  60 MPH
96H  29/0600Z 24.0N  56.0W   55 KT  65 MPH
120H  30/0600Z 25.5N  57.0W   55 KT  65 MPH

Forecaster Kelly