[Tropical] Tropical Cyclone Discussion

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WTNT42 KNHC 260248
TCDAT2

Tropical Storm Philippe Discussion Number  11
NWS National Hurricane Center Miami FL       AL172023
1100 PM AST Mon Sep 25 2023

There have not been many changes to the appearance of Philippe
tonight. The low-level circulation continues to be primarily exposed
to the west of a rather misshapen area of deep convection. While
there are a few convective cells that have attempted to redevelop
closer to the circulation center, the storm remains disrupted by
20-30 kt of westerly vertical wind shear. While subjective and
objective satellite intensity estimates continue to gradually
decrease, earlier GOES-16 1-minute meso sector low-level derived
motion winds north of Philippe were in the 50-60 kt range, which
typically would support somewhat higher winds. In addition, a
recently arriving ASCAT-C pass caught the eastern side of the
circulation, revealing peak winds in the 40-45 kt range. Therefore,
the initial intensity is adjusted to 45 kt for this advisory.

Despite the slightly higher initial intensity, Philippe's future
prospects appear increasingly dim (as a tropical cyclone), as the
current shear affecting the system is not expected to abate. In
fact, this shear may increase further after 48 hours. Because the
storm will still continue to traverse warm 29-30C sea-surface
temperatures, the storm is likely to continue generating convective
bursts east of the center for the majority of the forecast period.
However, it appears increasingly likely the shear will not be able
to be overcome, and the updated NHC intensity forecast now shows the
storm on a slow decline, ending with it becoming a remnant low
sometime in the day 4-5 time frame. This forecast is in good
agreement with the consensus aids, with remnant low status
occuring roughly when the ECMWF shows the system stopping to
produce organized convection.

Philippe appears to have resumed a more west-northwestward motion at
285/10 kt. Compared to 24 hours ago, the guidance has started to
come into better agreement that the storm should maintain a general
west-northwestward motion for the next 48-72 hours, not really
feeling the mid-level weakness developing to its north as it
gradually becomes more vertically shallow. The biggest change
compared to the prior advisory is showing a turn more westward by
the end of the forecast as the system becomes primarily steered by
the more east-to-west oriented low-level ridging. This leftward
adjustment to the track forecast is mainly in response to similar
leftward shifts in both the GFS and ECMWF ensemble guidance that
have shifted to weaker solutions steered by the low-level flow. The
NHC track lies roughly in between the reliable consensus aids (TVCN,
HCCA) and the ECMWF and its ensemble mean, which remain on the south
and west side of the guidance envelope.


FORECAST POSITIONS AND MAX WINDS

INIT  26/0300Z 17.6N  47.8W   45 KT  50 MPH
 12H  26/1200Z 18.0N  49.4W   45 KT  50 MPH
 24H  27/0000Z 18.8N  51.4W   40 KT  45 MPH
 36H  27/1200Z 19.8N  53.1W   40 KT  45 MPH
 48H  28/0000Z 20.8N  54.6W   35 KT  40 MPH
 60H  28/1200Z 21.5N  56.0W   35 KT  40 MPH
 72H  29/0000Z 22.0N  57.4W   35 KT  40 MPH
 96H  30/0000Z 22.0N  59.4W   30 KT  35 MPH
120H  01/0000Z 22.0N  61.4W   30 KT  35 MPH...POST-TROP/REMNT LOW

$$
Forecaster Papin
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