Tropical Storm Idalia Discussion Number 9
NWS National Hurricane Center Miami FL AL102023
400 PM CDT Mon Aug 28 2023

The satellite presentation of Idalia has continued to improve this
afternoon. The center of the storm is embedded within an area of
deep convection with cloud tops colder than -75C. Although the
early reconnaissance aircraft and radar data from Cuba
have not yet indicated the presence of an eyewall, the aircraft
data did indicate that the pressure had fallen to around 987 mb on
the final pass through the center earlier this afternoon.
Believable SFMR winds of 60 kt were reported to the east of the
center, and Idalia's intensity was raised to that value on the
1800 UTC intermediate advisory and it remains at that value for
this advisory. NOAA and Air Force Reserve Hurricane Hunter aircraft
are scheduled to be in the storm environment again this evening and
should provide additional information on the structure and
intensity of the tropical cyclone. Another NOAA G-IV synoptic
surveillance mission is underway and that data should be
assimilated into the dynamical model runs this evening.

Idalia is moving northward or 360/7 kt. The storm should continue
to be steered northward between a mid-level trough over the central
Gulf of Mexico and a ridge near the Greater Antilles through
tonight. On Tuesday, a faster north-northeastward motion should
begin as a trough moves into the east-central United States. This
motion should bring the center of Idalia to the Gulf coast of
Florida on Wednesday. The dynamical models continue to have some
spread after 36 hours, with the GFS and HAFS guidance along the
western side of the envelope and the ECMWF along the eastern side.
The consensus aids were slightly west of the previous cycle, and
the NHC forecast has been nudged in that direction. The NHC track
forecast is in best agreement with the HFIP corrected consensus
model. It is still worth stressing that only a small deviation in
the track could cause a significant change in Idalia's landfall
location in Florida due to the paralleling track to the west coast
of the state. When Idalia nears the Atlantic coast of the
southeastern United States the guidance suggests the cyclone will
turn more eastward as the aforementioned trough passes to the north
of the storm.

The upper-level wind pattern is forecast to become more conducive
for significant strengthening when Idalia moves over the
southeastern Gulf of Mexico tonight and Tuesday. At the same time,
the storm is forecast to move over an area of high ocean heat
content. These conditions are likely to allow for a period of
rapid strengthening which is explicitly shown in the official
forecast through 36 hours. Idalia is likely to become a hurricane
this evening, and is predicted to become major hurricane over the
eastern Gulf within 36 hours. The NHC intensity forecast is just a
little above the latest HFIP corrected consensus guidance.

Idalia is forecast to move into an area very susceptible to storm
surge, and regardless of the cyclone's landfall intensity, there is
increasing confidence of a significant storm surge event.


KEY MESSAGES:

1. There is a danger of life-threatening storm surge inundation
along portions of the Florida Gulf Coast where a Storm Surge Warning
is in effect, including Tampa Bay and the Big Bend region of
Florida. Inundation of 8 to 12 feet above ground level is expected
somewhere between Chassahowitzka and Aucilla River. Residents in
these areas should follow any advice given by local officials.

2. Hurricane conditions are expected within portions of the
Hurricane Warning area along the Florida Gulf Coast, with the
potential for destructive winds where the core of Idalia moves
onshore. Strong winds will also spread inland across portions of
northern Florida near the track of the center of Idalia.

3. Areas of flash and urban flooding, some of which may be locally
significant, are expected across portions of the west coast of
Florida, the Florida Panhandle, and southern Georgia Tuesday into
Wednesday, spreading into portions of the eastern Carolinas
Wednesday into Thursday.

4. Hurricane-force winds are expected across portions of far western
Cuba tonight. Heavy rainfall is also expected across portions
of western Cuba and may produce areas of flash and urban
flooding as well as landslides.


FORECAST POSITIONS AND MAX WINDS

INIT 28/2100Z 21.4N 85.1W 60 KT 70 MPH
12H 29/0600Z 22.7N 85.2W 75 KT 85 MPH
24H 29/1800Z 24.9N 85.0W 90 KT 105 MPH
36H 30/0600Z 27.6N 84.4W 105 KT 120 MPH
48H 30/1800Z 30.4N 82.9W 80 KT 90 MPH...INLAND
60H 31/0600Z 32.7N 80.4W 50 KT 60 MPH...INLAND
72H 31/1800Z 34.0N 76.8W 50 KT 60 MPH...OVER WATER
96H 01/1800Z 34.1N 71.4W 45 KT 50 MPH
120H 02/1800Z 34.0N 69.0W 45 KT 50 MPH

$$
Forecaster Brown