[Tropical] Tropical Cyclone Discussion

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Hurricane Idalia Discussion Number  16...Retransmitted
NWS National Hurricane Center Miami FL       AL102023
1100 AM EDT Wed Aug 30 2023

Although Idalia reached category 4 intensity early this morning
over the far northeastern Gulf of Mexico, Air Force Reserve
Hurricane Hunter data just before landfall indicated that the peak
winds had started to decrease and the minimum pressure had begun to
rise.  This was likely due to an eyewall replacement cycle (which
was shown by radar data) and an increase in shear over the
hurricane.  Idalia made landfall near Keaton Beach, Florida,
as a category 3 hurricane around 1145 UTC, and it has been
weakening quickly since then over northern Florida.  WSR-88D
Doppler velocities suggest that the maximum winds are now down to
about 80 kt.

Idalia is moving toward the north-northeast, or 030/17 kt.  The
hurricane is located between a subtropical ridging near the Greater
Antilles and a deep-layer trough over the eastern United States.
This pattern is expected to cause Idalia to turn toward the
northeast and then east during the next 36 hours, and the track
guidance is very good agreement on the center moving near the
coasts of Georgia, South Carolina, and North Carolina through
Thursday.  Model spread increases beyond 36 hours, although there
is not as much uncertainty as yesterday.  None of the models shows
the circulation curving back toward the U.S. anymore, but the
guidance is suggestive that Idalia will likely slow down as it
approaches Bermuda on days 3 through 5.  During that period, the
NHC track forecast is a blend of the previous forecast with the
current HCCA and TVCX consensus aids.

Relatively fast weakening is anticipated through the rest of the
day.  The intensity guidance is hovering right around the hurricane
threshold at 12 hours, and the official forecast therefore
conservatively shows a 65-kt hurricane near the Georgia/South
Carolina border this evening.  Idalia should become a tropical
storm by tonight while moving near the coast of South Carolina.
The intensity forecast is a little bit above the guidance at 24 and
36 hours to account for the possibility of a band of strong winds
developing on the back side of Idalia near eastern North Carolina,
associated with a nearby frontal boundary.  Beyond 36 hours, the
guidance suggests that Idalia's intensity is likely to hover
between 45-50 kt through the end of the forecast period.


KEY MESSAGES:

1. Significant impacts from storm surge will continue along the
Gulf coast of Florida within the Storm Surge Warning through this
evening.  Dangerous storm surge is also expected along the
southeastern U.S. coast within the Storm Surge Warning area tonight
and Thursday.  Residents in these areas should follow any advice
given by local officials.

2. Damaging hurricane-force winds will occur where the core of
Idalia moves across southern Georgia and southern South Carolina
within the hurricane warning area through this evening.  Residents
in these areas should be prepared for long-duration power outages.
Strong winds are also expected to spread northeastward across South
Carolina and North Carolina through Thursday within the Tropical
Storm Warning area.

3. Areas of flash, urban, and moderate river flooding, with
considerable impacts, are expected from portions of North Florida
through central Georgia and South Carolina, through eastern North
Carolina into Thursday.


FORECAST POSITIONS AND MAX WINDS

INIT  30/1500Z 30.6N  83.2W   80 KT  90 MPH...INLAND
 12H  31/0000Z 32.4N  81.1W   65 KT  75 MPH...INLAND
 24H  31/1200Z 33.8N  77.6W   55 KT  65 MPH...OVER WATER
 36H  01/0000Z 33.9N  74.0W   50 KT  60 MPH
 48H  01/1200Z 33.2N  71.1W   45 KT  50 MPH
 60H  02/0000Z 32.4N  69.1W   45 KT  50 MPH
 72H  02/1200Z 31.9N  68.0W   50 KT  60 MPH
 96H  03/1200Z 31.4N  66.3W   50 KT  60 MPH
120H  04/1200Z 32.5N  63.3W   50 KT  60 MPH

$$
Forecaster Berg
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