[Tropical] Tropical Cyclone Discussion

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WTNT42 KNHC 241442
TCDAT2

Tropical Storm Philippe Discussion Number   5
NWS National Hurricane Center Miami FL       AL172023
1100 AM AST Sun Sep 24 2023

Philippe is a challenging tropical cyclone to analyze this morning.
On one hand, the overall satellite presentation has improved since
yesterday, and a 0907Z SSMIS microwave pass shows a possible
mid-level eye.  Yet the 1-min GOES16 imagery reveals a weak
low-level swirl southwest of the main convective blob, and ASCAT-B
near 12Z showed a disorganized inner core with less wind than one
might expect (albeit very contaminated with rain).  Overall,
intensity estimates have risen since the last advisory, so the
initial wind speed is set to 45 kt, similar to the TAFB/SAB values,
but this should be considered fairly uncertain.

Little change in intensity is forecast with the storm during the
next couple of days as increasing shear is forecast to otherwise
counteract a conducive environment.  There are a variety of
solutions after that point, with some models showing a stronger
Philippe after finding a lower-shear environment, while others
suggesting that the storm succumbs to the shear from an
upper-level trough.  There are no easy answers here with moderate
shear cases in high SST/moisture conditions well known to have
higher errors due to an inherent lack of predictability.  The new
forecast splits the difference in the model guidance, lying near
the consensus and the previous forecast, and we will just have to
see if a trend emerges for the eventual intensity of Philippe.

The long-term motion of the storm is westward or 280/10 kt. The
subtropical ridge to the north of Philippe is forecast to gradually
weaken and slide eastward in a day or two, allowing the tropical
storm to move more west-northwestward and northwestward by the
middle of the week.  Uncertainty grows after that point, with the
track seemingly dependent on the intensity.  A stronger system
would probably turn northward, like the GFS/HWRF/HMON models, while
a weaker one, like the UKMET/ECMWF solutions, would take a left
turn under the low-level subtropical ridge.  For now, little change
was made to the long-range forecast given all of the uncertainty.


FORECAST POSITIONS AND MAX WINDS

INIT  24/1500Z 16.2N  41.7W   45 KT  50 MPH
 12H  25/0000Z 16.5N  43.3W   45 KT  50 MPH
 24H  25/1200Z 16.9N  45.6W   45 KT  50 MPH
 36H  26/0000Z 17.4N  47.8W   45 KT  50 MPH
 48H  26/1200Z 18.0N  49.7W   45 KT  50 MPH
 60H  27/0000Z 18.9N  51.0W   50 KT  60 MPH
 72H  27/1200Z 20.0N  52.5W   50 KT  60 MPH
 96H  28/1200Z 22.5N  54.5W   55 KT  65 MPH
120H  29/1200Z 24.0N  55.5W   55 KT  65 MPH

$$
Forecaster Blake
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