[Tropical] Tropical Cyclone Discussion

[EMWIN Server]

WTNT42 KNHC 272038
TCDAT2

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.


FORECAST POSITIONS AND MAX WINDS

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
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