[Tropical] Tropical Cyclone Discussion

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WTNT42 KNHC 022056
TCDAT2

Tropical Storm Philippe Discussion Number  38
NWS National Hurricane Center Miami FL       AL172023
500 PM AST Mon Oct 02 2023

The center of Philippe remains exposed this afternoon with
some convection firing closer to the center over the last few
hours. Heavy rainfall and thunderstorms remain displaced to the
south and southeast of the center as high northwesterly vertical
wind shear persists. The initial intensity is again held steady at
45 kt for this advisory, consistent with SFMR data from the Air
Force Reserve reconnaissance aircraft mission showing a large area
of 40-45 surface winds mostly on the east and southeast side of the
system earlier this afternoon. Another Air Force Reserve mission is
scheduled for this evening.

The storm continues to move to the northwest (305 degrees) at 6 kt
this afternoon.  Philippe refuses to gain much vertical depth as a
tropical cyclone and has been steered more by the lower-level
ridge.  Thus, the track forecast is again adjusted westward to
match recent satellite trends and in line with the weaker model
guidance.  The cyclone is forecast to pass near Barbuda tonight
before turning north-northwest north of the Leeward Islands.
Around mid-week, Philippe should turn northward due to flow between
a mid-level trough in the southwest Atlantic and the subtropical
ridge.  Uncertainty greatly increases after that point, with huge
differences showing up between the GFS- and ECMWF-based guidance.
The differences in model track forecasts are related to whether this
trough captures Philippe's circulation, causing Philippe to move
more to the north-northwest, or whether it is shunted more to the
northeast ahead of the trough.  Consistent with model guidance, the
track forecast has shifted farther west from the previous advisory
and is in line with the consensus aids and mean ensemble track
guidance. Further adjustments to the west may be necessary.

Strong northwesterly vertical wind shear is expected to
prevent significant strengthening in the short term. Shear is
forecast to decrease a bit for a short period of time in the next 2
to 3 days and could allow for some strengthening.  However, almost
all of the guidance is showing a less conducive environment, and
the NHC forecast reflects this trend, lying on the high end of
model guidance but in line with HCCA.  The uncertainty is extremely
large at the end of the forecast period as some models are now
showing an extratropical transition due to the mid-latitude trough,
but a lot depends on how strong Philippe eventually becomes, which
has clearly not been very predictable during this storm's lifetime.


KEY MESSAGES:

1. Tropical storm conditions are expected across Barbuda and
Antigua beginning this evening while Philippe passes near and
north of the area.  Interests elsewhere in the northern Leeward
Islands should continue to monitor this system.

2. Heavy rainfall from Philippe could produce isolated to scattered
flash flooding over the northern Leeward Islands, particularly
across Barbuda and Antigua, through Tuesday.


FORECAST POSITIONS AND MAX WINDS

INIT  02/2100Z 17.6N  61.5W   45 KT  50 MPH
 12H  03/0600Z 18.2N  62.2W   45 KT  50 MPH
 24H  03/1800Z 19.1N  62.6W   45 KT  50 MPH
 36H  04/0600Z 20.6N  63.0W   45 KT  50 MPH
 48H  04/1800Z 22.2N  63.4W   45 KT  50 MPH
 60H  05/0600Z 23.9N  63.8W   50 KT  60 MPH
 72H  05/1800Z 26.0N  63.8W   55 KT  65 MPH
 96H  06/1800Z 30.6N  62.2W   60 KT  70 MPH
120H  07/1800Z 35.0N  60.0W   65 KT  75 MPH

$$
Forecaster Blake/Stevenson
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