[Tropical] Tropical Cyclone Discussion

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WTNT45 KNHC 212045
TCDAT5

Hurricane Tammy Discussion Number  14
NWS National Hurricane Center Miami FL       AL202023
500 PM AST Sat Oct 21 2023

Tammy passed just east of Guadeloupe around 18Z and is now located
near Antigua.  Radar imagery continues to show a tight and
well-organized inner core, and the earlier aircraft data indicated
that the hurricane-force winds were confined to that region.
Despite Tammy having passed just east of Dominica and Guadeloupe
today, surface observations indicate that winds did not get
particularly high at those locations due to Tammy being a very
compact hurricane.  The initial intensity is held at 75 kt based on
the earlier aircraft data and steady state appearance in radar
images.  Both the NOAA and Air Force Hurricane Hunters are
scheduled to investigate Tammy again this evening.

The hurricane is moving north-northwestward, 335 degrees, at 9 kt.
A continued northwest to north-northwest motion is expected during
the next 12-24 hours, taking the core of Tammy over or just east of
the Leeward Islands during that time.  After the hurricane pulls
north of the islands on Sunday, a turn to the north seems likely
when the system moves in the flow between a ridge over the central
Atlantic and a large trough over the western Atlantic.  The spread
in the guidance continues to be very large in the 4- and 5-day time
frame.  In fact, the difference in the model predicted center
positions of Tammy at day 5 is more than 1000 miles.  The NHC
intensity forecast is similar is the previous one through day 3, but
is again slower than the earlier forecast at days 4 and 5, trending
toward the HCCA guidance.

Tammy is expected to remain over very warm 29 to 30 C SSTs during
the next few days, however, it will also remain in a moderate wind
shear environment.  These conditions will likely result in slow
strengthening during the next few days.  The opportunity for
strengthening will likely end early next when Tammy moves into a
region of stronger shear, which should cause a weakening trend.  The
NHC intensity is again nudged upward, trending toward the latest
consensus models.  However, the intensity forecast at long range is
of low confidence since Tammy's future strength will likely be
correlated to the track.


KEY MESSAGES:

1.  Hurricane and tropical storm conditions are expected in portions
of the Leeward Islands through early Sunday.

2.  The heaviest rains from Tammy will continue over the Leeward
Islands through Sunday. This rainfall may produce isolated flash and
urban flooding, along with isolated mudslides in areas of higher
terrain.

3.  A storm surge could produce coastal flooding in areas of onshore
winds as the center of Tammy moves near or over the Leeward Islands.
Near the coast, the surge will be accompanied by large and dangerous
waves.


FORECAST POSITIONS AND MAX WINDS

INIT  21/2100Z 17.0N  61.3W   75 KT  85 MPH
 12H  22/0600Z 18.1N  62.1W   75 KT  85 MPH
 24H  22/1800Z 19.5N  62.9W   80 KT  90 MPH
 36H  23/0600Z 20.9N  63.5W   85 KT 100 MPH
 48H  23/1800Z 22.2N  63.7W   85 KT 100 MPH
 60H  24/0600Z 23.1N  63.6W   85 KT 100 MPH
 72H  24/1800Z 23.8N  63.4W   85 KT 100 MPH
 96H  25/1800Z 25.6N  62.9W   75 KT  85 MPH
120H  26/1800Z 28.0N  62.6W   60 KT  70 MPH

$$
Forecaster Cangialosi
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