Tropical Storm Philippe Discussion Number  45
NWS National Hurricane Center Miami FL       AL172023
1100 AM AST Wed Oct 04 2023

Visible satellite images this morning indicate that Philippe's
low-level circulation remains elongated, and the center is still
located on the northwestern edge of an area of deep convection.
This convective activity continues to produce heavy rains over the
U.S. and British Virgin Islands, as well as northeastern Puerto
Rico.  The initial intensity remains 40 kt based on a blend of the
latest subjective and objective satellite estimates, with sustained
tropical-storm-force winds limited to the eastern semicircle.

Philippe has turned toward the north-northwest with an initial
motion of 335/6 kt.  The flow between a strong mid-tropospheric
high over the central Atlantic and a deep-layer trough just off the 
east coast of Florida is expected to steer Philippe northward, and 
at a faster forward speed, beginning tonight and continuing for the 
next few days.  The track guidance is in good agreement on this 
general scenario, although there is some east-to-west spread among 
the models related to how Philippe interacts with a non-tropical 
low that is forecast to develop to its west in about 2-3 days.  
After day 3, a deeper trough is forecast to swing across eastern 
North America, and much of the guidance suggests that Philippe 
might bend back to the left a bit and approach Atlantic Canada or 
eastern Maine in 3-4 days.  Overall, the NHC track forecast is near 
the middle of the guidance envelope, close to the TVCX and HCCA 
consensus aids, and is also nearly identical to the previous 
prediction.

Overall, moderate-to-strong vertical shear is expected to persist 
over Philippe during the next few days, and very little change in 
intensity is forecast during that time.  Once Philippe begins to 
interact with the developing low pressure to its west and the 
associated upper-level trough, baroclinic influences could support 
some strengthening.  This strengthening is shown by most of the 
intensity models, including the GFS and ECMWF global models, and 
the official forecast therefore shows a peak intensity of 50 kt at 
60 and 72 hours.  Model-based phase-space diagrams, simulated 
satellite imagery, and SHIPS diagnostics all suggest that Philippe 
will become attached to a front between days 3 and 4 to the north 
of Bermuda, and the official forecast therefore shows a completion 
of extratropical transition by Sunday morning.


KEY MESSAGES:

1. Heavy rainfall from Philippe is expected to produce scattered 
flash flooding across portions of the U.S. and British Virgin 
Islands through today.  Heavy rainfall from Philippe will begin to 
affect Bermuda on Thursday. 

2. Tropical storm conditions are possible on Bermuda beginning 
Friday morning, and a Tropical Storm Watch is now in effect for the 
island.

3. Philippe is likely to move over portions of Atlantic Canada and 
eastern New England, likely as a post-tropical cyclone, this 
weekend.  Regardless of Philippe's intensity or structure, 
interests in those areas should monitor the storm's progress and be 
prepared for the possibility of strong winds and heavy rainfall.


FORECAST POSITIONS AND MAX WINDS

INIT  04/1500Z 21.2N  65.7W   40 KT  45 MPH
12H  05/0000Z 22.3N  66.0W   40 KT  45 MPH
24H  05/1200Z 24.7N  66.2W   40 KT  45 MPH
36H  06/0000Z 27.6N  65.9W   45 KT  50 MPH
48H  06/1200Z 30.8N  65.3W   45 KT  50 MPH
60H  07/0000Z 34.2N  65.1W   50 KT  60 MPH
72H  07/1200Z 37.8N  65.3W   50 KT  60 MPH
96H  08/1200Z 46.8N  67.8W   45 KT  50 MPH...POST-TROP/EXTRATROP
120H  09/1200Z 52.9N  71.9W   25 KT  30 MPH...POST-TROP/EXTRATROP

$$
Forecaster Berg