Official Discussion issued by the National Hurricane Center

Philippe (AL172023) DATA RELEASED: 9/27/2023 9:00:00 PM UTC

Copy of official data

Tropical Storm Philippe Discussion Number  18
NWS National Hurricane Center Miami FL       AL172023
500 PM AST Wed Sep 27 2023

Philippe's convection continues to oscillate this afternoon. Shortly 
after the previous advisory, the convection waned and has become 
less organized. An ASCAT-C pass showed that the center of the system 
has become more ill-defined, with the low-level center difficult to 
pinpoint this afternoon. Convection continues to redevelop back to 
the east, with the expected mean center on the west side of the 
convection. This was further supported by an AMSR microwave 
overpass depicting and overall lack of organization. Subjective 
Dvorak data-T numbers have come down with the current intensity 
estimates remaining at 3.0. Given the earlier ASCAT-B pass and the 
CI intensity estimates, the initial intensity will is held at 45 
kt, but this could be generous.

This is a fairly complicated intensity and track forecast. Philippe 
is in a sheared environment, and currently lacks organization. The 
system is forecast to move into a slightly drier mid-level airmass 
in a few days, which may also inhibit the overall convective 
pattern. Some slight fluctuations in intensity may occur due to the 
pulsing convective nature of the system during the next few days, 
with an overall slow weakening trend later this weekend. There 
remains uncertainty in the intensity forecast and it is possible 
Philippe maintains its tropical cyclone status as it reaches the 
northern Leeward Islands, or the system could weaken and open into 
a trough.

The estimated motion is west-northwestward at 4 kt.  Philippe is 
currently being steered by the flow around a weak mid-level ridge 
and is expected to move west-northwestward over the next couple of 
days. In the latter part of the forecast period, a weakening and 
shallow system should turn toward the west-southwest. There is 
unusually large spread in the model guidance this cycle with the GFS 
and ECMWF over 1100 miles apart on Day 5. The GFS is stronger and on 
the right side, of the guidance envelope which has pulled the 
consensus aids right as well. The ECMWF is weaker and on the left 
side of the guidance. The track forecast is highly dependent on the 
intensity forecast, however. The official track forecast is similar 
to the previous forecast, just slower given the initial slower 
motion, which is closest to the ECMWF. 


INIT  27/2100Z 17.7N  54.0W   45 KT  50 MPH
12H  28/0600Z 18.1N  55.1W   45 KT  50 MPH
24H  28/1800Z 18.6N  56.5W   40 KT  45 MPH
36H  29/0600Z 18.9N  57.7W   40 KT  45 MPH
48H  29/1800Z 18.9N  58.8W   40 KT  45 MPH
60H  30/0600Z 18.8N  60.0W   35 KT  40 MPH
72H  30/1800Z 18.7N  61.6W   35 KT  40 MPH
96H  01/1800Z 18.4N  64.0W   30 KT  35 MPH...POST-TROP/REMNT LOW
120H  02/1800Z 18.2N  66.3W   30 KT  35 MPH...POST-TROP/REMNT LOW

Forecaster Kelly