[Tropical] Tropical Cyclone Discussion

[EMWIN Server]

WTNT43 KNHC 051459
TCDAT3

Tropical Depression Thirteen Discussion Number   1
NWS National Hurricane Center Miami FL       AL132023
1100 AM AST Tue Sep 05 2023

Satellite images indicate that the tropical wave (Invest AL95) that
we have been following for several days has become better organized
this morning, with many curved low-level banding features.  A
partial scatterometer pass near 1201 UTC indicated a well-defined
center had formed, with winds speeds of about 30 kt.  Thus,
advisories have been initiated on Tropical Depression Thirteen, and
the current intensity is set to 30 kt.

The depression is moving west-northwestward at about 13 kt.  A
mid-level ridge over the central Atlantic is expected to persist to
the north of the tropical cyclone, keeping the system moving with
this general motion through Saturday.  The spread in the model
guidance is remarkably low for a first advisory, and the official
forecast is near or west of the model consensus.  However, it
should be noted that the NOAA corrected-consensus aids and some
ensemble members are still to the left of the official forecast, so
it is too early to determine exactly how close this system will get
to the Leeward Islands given the average track forecast error at
those time ranges.

The environment around the depression appears to be conducive for
strengthening.  The only obvious hindering factor is
light-to-moderate northeasterly shear, which should keep the
intensification rate in check in the short term.  However, in two to
three days, this shear is forecast to relax with an upper-level
ridge building near the cyclone, and the system should be moving
over record-warm waters of near 30 deg C east of the Lesser Antilles
(that would look more in place in the Gulf of Mexico).  These
factors could support rapid intensification by the end of the week,
although it too early to determine exactly when this might occur
until a better-defined inner core forms.  The NHC intensity forecast
is extremely bullish for a first forecast, but remarkably lies
below the intensity consensus.  All indications are that the
depression will become a strong hurricane by the end of the forecast
period.

KEY MESSAGES:

1. The depression is forecast to become a major hurricane by
this weekend and could bring impacts to the Leeward Islands by that
time. While it is too soon to determine the location and magnitude
of these possible impacts, interests in this area should monitor
the progress of the depression and updates to the forecast.

FORECAST POSITIONS AND MAX WINDS

INIT  05/1500Z 12.5N  40.2W   30 KT  35 MPH
 12H  06/0000Z 12.8N  42.1W   40 KT  45 MPH
 24H  06/1200Z 13.6N  44.7W   50 KT  60 MPH
 36H  07/0000Z 14.4N  47.2W   60 KT  70 MPH
 48H  07/1200Z 15.3N  49.7W   70 KT  80 MPH
 60H  08/0000Z 16.2N  52.2W   80 KT  90 MPH
 72H  08/1200Z 17.3N  54.7W   95 KT 110 MPH
 96H  09/1200Z 19.4N  59.1W  115 KT 130 MPH
120H  10/1200Z 21.5N  63.5W  120 KT 140 MPH

$$
Forecaster Blake
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