[Tropical] Tropical Cyclone Discussion

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WTNT42 KNHC 042038
TCDAT2

Tropical Storm Philippe Discussion Number  46
NWS National Hurricane Center Miami FL       AL172023
500 PM AST Wed Oct 04 2023

Philippe still has an elongated circulation with discrete clusters
of deep convection extending well to the east and south of the
center.  Aircraft and satellite-derived wind data suggest that the
maximum winds have decreased a bit, and Philippe is barely a
tropical storm.  An Air Force Reserve Hurricane Hunter aircraft
only measured peak 850-mb flight-level winds of 39 kt, and although
SFMR winds were reported between 35-40 kt, a comparison with ASCAT
data and a visual assessment from the flight crew indicate that
these data were at least 10 kt too high.  The consensus of all
available data suggest that 35 kt is a more representative value
for the initial intensity.

The latest fixes indicate that Philippe has turned northward with
an initial motion of 350/10 kt.  A northward motion with an
increase in forward speed is expected through the next 3 days while
Philippe moves between a deep-layer trough just east of Florida and
the subtropical ridge over the central Atlantic.  After day 3, a
larger trough is forecast to move across eastern North America and
become negatively tilted, which is expected to cause Philippe to
bend to the north-northwest when it reaches Atlantic Canada or
eastern New England over the weekend.  The track models (at
least the ones that carry Philippe for the entire forecast period)
remain in good agreement on this scenario, and the NHC track
forecast is close to the HCCA consensus aid.

The forecast for Philippe's intensity and structure remains complex.
The 12Z GFS still shows a separate non-tropical low developing over
the western Atlantic, with Philippe becoming absorbed by the warm
front to the east of the low in 2-3 days.  However, that appears to
be an outlier scenario at this time since the ECMWF, UKMET, and
Canadian models keep Philippe as a distinct and dominant low.  Even
if it doesn't become absorbed, Philippe is likely to become
frontal by day 3, and the NHC forecast now shows the system as
extratropical by Saturday afternoon.  Little change in strength is
likely during the next couple of days, but Philippe could strengthen
a little due to baroclinic influences while it goes through
extratropical transition.  The NHC intensity forecast is below the
intensity consensus aids for the first 48 hours, but then is between
IVCN and the ECMWF after that time.


KEY MESSAGES:

1. Tropical storm conditions are expected on Bermuda beginning
early Friday morning, and a Tropical Storm Warning is now in effect.
Heavy rainfall will begin to affect the island on Thursday.

2. 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  04/2100Z 22.6N  65.9W   35 KT  40 MPH
 12H  05/0600Z 24.0N  66.1W   35 KT  40 MPH
 24H  05/1800Z 26.6N  66.0W   35 KT  40 MPH
 36H  06/0600Z 29.8N  65.7W   40 KT  45 MPH
 48H  06/1800Z 33.3N  65.3W   45 KT  50 MPH
 60H  07/0600Z 36.9N  65.4W   50 KT  60 MPH
 72H  07/1800Z 40.9N  65.9W   50 KT  60 MPH...POST-TROP/EXTRATROP
 96H  08/1800Z 50.5N  69.5W   40 KT  45 MPH...POST-TROP/EXTRATROP
120H  09/1800Z...DISSIPATED

$$
Forecaster Berg
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