[Tropical] Tropical Cyclone Discussion

[EMWIN Server]

WTNT43 KNHC 060837
TCDAT3

Tropical Storm Lee Discussion Number   4
NWS National Hurricane Center Miami FL       AL132023
500 AM AST Wed Sep 06 2023

Lee continues to strengthen at a quick pace.  Satellite images show
that deep convection has been increasing in intensity and coverage
in a central dense overcast feature and in a sprawling curved band
over the western semicircle.  The Dvorak classifications from TAFB
and SAB are now 3.5/55 kt, and accordingly, the initial intensity
has been increased to 55 kt.  Lee is not far from hurricane
strength, and it likely will achieve that status later today.

The tropical storm is moving west-northwestward at 14 kt on the
south side of a subtropical ridge over the central Atlantic.  This
ridge is expected to persist to the north of Lee during the next
several days, keeping the storm on a west-northwest track through
the remainder of the week and over the weekend.  Although the NHC
forecast and the model guidance continue to show Lee passing to the
north of the northern Leeward Islands this weekend, users are
reminded that the details of the track forecast are still uncertain
at those time ranges.  For reference, the average NHC forecast track
errors are around 125 and 175 n mi on days 4 and 5, respectively.
The NHC track forecast lies on the southern side of the model
guidance envelope, roughly halfway between the usually most skillful
consensus aids, HCCA and TVCA.

Lee has already been strengthening fairly quickly despite some
east-northeasterly vertical wind shear over the system.  Since the
shear is expected to relax while the storm remains over very warm
water and in a moist environment, continued steady to rapid
intensification is expected during the next few days.  Most of the
intensity models are very aggressive, bringing Lee to major
hurricane status by the weekend, but they don't show much change in
strength in the short term.  In addition, even the global models
like the GFS and ECMWF show explosive intensification and forecast
Lee's minimum pressure to drop by more than 60 mb by the end of the
forecast period.  The NHC intensity forecast lies near the high end
of the model guidance during the next 24-48 hours, but falls to near
the middle of the guidance envelope after that.  Regardless of the
details, there is high confidence that Lee will be a powerful
hurricane late this week and over the weekend.

KEY MESSAGES:

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


FORECAST POSITIONS AND MAX WINDS

INIT  06/0900Z 13.7N  44.6W   55 KT  65 MPH
 12H  06/1800Z 14.3N  46.4W   70 KT  80 MPH
 24H  07/0600Z 15.1N  48.8W   80 KT  90 MPH
 36H  07/1800Z 16.0N  51.3W   90 KT 105 MPH
 48H  08/0600Z 17.0N  53.7W  105 KT 120 MPH
 60H  08/1800Z 18.1N  56.2W  120 KT 140 MPH
 72H  09/0600Z 19.2N  58.4W  130 KT 150 MPH
 96H  10/0600Z 21.1N  62.4W  130 KT 150 MPH
120H  11/0600Z 22.7N  65.5W  130 KT 150 MPH

$$
Forecaster Cangialosi
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