[Tropical] Tropical Cyclone Discussion

[EMWIN Server]

WTNT42 KNHC 300237
TCDAT2

Tropical Storm Philippe Discussion Number  27
NWS National Hurricane Center Miami FL       AL172023
1100 PM AST Fri Sep 29 2023

Deep convection continues to pulse over the southeastern portion of
Philippe's circulation this evening.  The center is located near
the northwestern edge of the deep convection due to moderate
westerly shear.  The intensity is held at 45 kt, and is based on
the earlier reconnaissance aircraft data and a T3.0 (45 kt)
subjective Dvorak classification from TAFB.  Another Air Force
Reserve reconnaissance mission is scheduled overnight, and this
mission should provide a full assessment of Philippe's structure
and intensity.

The earlier aircraft center fixes and more recent satellite
position estimates indicate that Philippe is moving slowly
southwestward. This motion is being influenced by Philippe's
interaction with Tropical Storm Rina located to Philippe's
east-northeast.  As the two tropical cyclone's continue to
interact, Philippe is expected to move slowly west-southwestward
to westward during the next 24 to 36 hours.  After that time, the
distance between the tropical cyclones should increase, and
Philippe is forecast to turn northwestward when a mid-level ridge
builds over the central Atlantic.  After 72 hours, Philippe is
expected to turn northward between the aforementioned ridge and a
mid- to upper-level trough over the southwestern Atlantic.
Although the models are in general agreement on this scenario,
there is significant spread on the longitude of the northward turn,
and on how fast Philippe moves later in the period.  The updated
NHC track forecast is near the various consensus aids, and very
close to the previous advisory.

The moderate shear that has been affecting Philippe the past few
days could lessen during the next day or two.  This should allow
for some gradual strengthening over the weekend.  After that time,
there is a bifurcation in the intensity guidance with the
GFS-based SHIPS model, the HMON, the HWRF, and even the GFS showing
a more favorable upper-air environment and more significant
deepening with a track farther east.  Meanwhile, the ECMWF-based
SHIPS guidance, and the HAFS-A and HAFS-B which show a more westward
track keeps stronger southwesterly vertical wind shear over the
storm and therefore less strengthening.  The NHC intensity foreast
is near the middle of these two scenarios, but is a bit more
conservative than the lastest intensity consensus models.


FORECAST POSITIONS AND MAX WINDS

INIT  30/0300Z 17.6N  55.8W   45 KT  50 MPH
 12H  30/1200Z 17.3N  56.0W   45 KT  50 MPH
 24H  01/0000Z 17.2N  56.4W   50 KT  60 MPH
 36H  01/1200Z 17.3N  56.9W   55 KT  65 MPH
 48H  02/0000Z 17.8N  57.5W   60 KT  70 MPH
 60H  02/1200Z 18.7N  58.2W   60 KT  70 MPH
 72H  03/0000Z 20.2N  58.7W   60 KT  70 MPH
 96H  04/0000Z 23.4N  58.9W   60 KT  70 MPH
120H  05/0000Z 27.3N  57.5W   60 KT  70 MPH

$$
Forecaster Brown
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