[Tropical] Tropical Cyclone Discussion

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WTNT42 KNHC 020236
TCDAT2

Tropical Storm Philippe Discussion Number  35
NWS National Hurricane Center Miami FL       AL172023
1100 PM AST Sun Oct 01 2023

Philippe's cloud pattern has not become significantly better
organized since earlier today.  The system is still producing very
deep convection with cloud tops to -80 deg C or colder mainly over
the southeastern quadrant of the circulation.  There are no obvious
curved convective banding features at this time.  Some new
thunderstorms have developed near and over the center and this was
noted by the Air Force Hurricane Hunters who have been investigating
the storm this evening.  Observations from the aircraft indicate
little change in strength, with peak SFMR-observed surface winds
near 45 kt.

The tropical cyclone has moved rather slowly over the past several
hours and the initial motion estimate is west-northwestward, or
300/4 kt.  Philippe should turn northwestward to northward along
the western periphery of a mid-level high pressure area for the
next few days.  Then, the system should turn north-northeastward
and move through a weakness in the ridge.  The track guidance
through 48 hours has shifted eastward on this cycle.  In an attempt
to maintain continuity from the previous forecasts, the NHC track
is not shifted eastward as much as shown by the model consensus,
and the change through 24 hours is fairly slight.  Late in the
forecast period, there is uncertainty as to how soon the cyclone
will move into the higher-latitude westerlies.  The new GFS model
run suggests that the system may turn eastward and stay in the
subtropics through 5 days.  If this turns out to be true, then
Philippe could have a prolonged existence.

The environment for Philippe in the short term does not appear
conducive for significant strengthening, with fairly strong
westerly vertical wind shear likely to continue to affect the
system through Monday.  When the system moves farther north over
the Atlantic, it may encounter a region of reduced shear as
indicated by some of the dynamical guidance.  The official forecast
still shows the system becoming a hurricane in the 3- to 5-day time
frame and this is also supported by the IVCN model intensity
guidance.


KEY MESSAGES:

1. Tropical storm conditions are possible across portions of the
northern Leeward Islands Monday and Monday night while Philippe
passes near or just northeast of the area, and a Tropical Storm
Watch is in effect for Antigua and Barbuda.  Interests elsewhere
in the northern Leeward Islands should continue to monitor this
system as additional watches or warnings could be required later
tonight or Monday.

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


FORECAST POSITIONS AND MAX WINDS

INIT  02/0300Z 16.6N  59.1W   45 KT  50 MPH
 12H  02/1200Z 17.0N  59.8W   45 KT  50 MPH
 24H  03/0000Z 17.8N  60.7W   45 KT  50 MPH
 36H  03/1200Z 19.0N  61.3W   50 KT  60 MPH
 48H  04/0000Z 20.3N  61.7W   50 KT  60 MPH
 60H  04/1200Z 22.0N  61.8W   50 KT  60 MPH
 72H  05/0000Z 23.8N  61.7W   55 KT  65 MPH
 96H  06/0000Z 27.5N  60.2W   65 KT  75 MPH
120H  07/0000Z 30.1N  57.6W   75 KT  85 MPH

$$
Forecaster Pasch
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