Hurricane Idalia Discussion Number  13
NWS National Hurricane Center Miami FL       AL102023
500 PM EDT Tue Aug 29 2023

The first stages of an eye have been taking shape in visible
satellite imagery.  The hurricane has a relatively small Central
Dense Overcast and a prominent band of deep convection extending
over the eastern semicircle, reaching across the Florida peninsula
southward across western Cuba.  An Air Force Reserve Hurricane 
Hunter aircraft just measured a peak 700-mb flight-level wind of 91 
kt with the pressure falling to 972 mb.  The initial intensity is 
therefore set at 85 kt.

Idalia is moving faster toward the north, or 360/14 kt, between a
mid-level trough over the northwestern Gulf of Mexico and a
subtropical ridge over the Greater Antilles.  Idalia is expected to
continue moving northward and turn north-northeastward as it
approaches the Big Bend region of Florida during the next 12-24
hours.  There is very little spread among the track guidance, and
the NHC official forecast has been placed very close to the HCCA
and TVCX consensus aids during the first 24 hours.  This has
resulted in a westward shift of about 20-25 n mi compared to the
previous forecast, although it should be stressed that additional
shifts to the track will be possible until the center reaches land.

After landfall, Idalia is expected to turn toward the northeast and
then east, moving near or along the coast of Georgia and the
Carolinas in 36-48 hours.  Uncertainty in the track forecast is
still quite large after 48 hours, with many of the global models
turning Idalia southward, while some of the regional hurricane
models still show the storm moving out to sea.  As a result, the
official track forecast continues to show slow motion on days 4 and
5.

The 12-hour intensity forecast shows a 100-kt major hurricane.  It
is imperative to realize that Idalia is expected to continue
strengthening beyond that time, possibly close to the 110 kt shown
in the previous forecast, before the center reaches land.
Weakening is expected after landfall, but due to the system's
expected fast motion, it is possible that Idalia could maintain
hurricane intensity as it moves across southern Georgia and 
approaches the coasts of Georgia and South Carolina.  After 
Idalia's center moves offshore over the western Atlantic, strong 
shear is likely to limit re-intensification, and the official 
forecast essentially flatlines the intensity on days 2-5.


KEY MESSAGES:

1. Catastrophic impacts from storm surge inundation of 10 to 15 feet 
above ground level and destructive waves are expected somewhere 
between Aucilla River and Yankeetown, Florida. Life-threatening 
storm surge inundation is likely elsewhere along portions of the 
Florida Gulf Coast where a Storm Surge Warning is in effect.  
Residents in these areas should follow any advice given by local 
officials.

2. There is the potential for destructive life-threatening winds 
where the core of Idalia moves onshore in the Big Bend region of 
Florida, with hurricane conditions expected elsewhere in portions of 
the Hurricane Warning area along the Florida Gulf Coast. Strong 
winds will also spread inland across portions of northern Florida 
and southern Georgia near the track of the center of Idalia where 
Hurricane Warnings are in effect. Residents in these areas should be 
prepared for long-duration power outages. Damaging hurricane-force 
winds are possible in portions of eastern Georgia and southeastern 
South Carolina where Hurricane Watches are in effect. 

3. Areas of flash, urban, and moderate river flooding, with locally 
considerable impacts, are expected across the Florida Big Bend, 
central Georgia and South Carolina, through eastern North Carolina 
later tonight into Thursday.



FORECAST POSITIONS AND MAX WINDS

INIT  29/2100Z 26.1N  84.8W   85 KT 100 MPH
12H  30/0600Z 28.3N  84.5W  100 KT 115 MPH
24H  30/1800Z 31.0N  82.9W   75 KT  85 MPH...INLAND
36H  31/0600Z 32.9N  80.2W   50 KT  60 MPH...INLAND
48H  31/1800Z 33.9N  77.1W   45 KT  50 MPH...OVER WATER
60H  01/0600Z 33.8N  74.2W   45 KT  50 MPH
72H  01/1800Z 33.3N  71.8W   45 KT  50 MPH
96H  02/1800Z 32.3N  69.6W   45 KT  50 MPH
120H  03/1800Z 31.7N  69.0W   45 KT  50 MPH

$$
Forecaster Berg