Tropical Storm Idalia Discussion Number 5
NWS National Hurricane Center Miami FL AL102023
400 PM CDT Sun Aug 27 2023

Idalia's cloud pattern is gradually becoming a little better
organized, with a curved convective band forming over the southern
semicircle of the circulation. Upper-level outflow is currently
restricted over the northern portion of the system, however.
The advisory intensity is held at 35 kt based on a subjective
Dvorak estimate from TAFB. Another aircraft reconnaissance mission
into the storm is scheduled for tonight.

The tropical cyclone continues to move rather slowly, and the
initial motion estimate is 040/3 kt. Idalia should remain in a weak
steering pattern through tonight so slow and possibly erratic
motion is likely for the next 12 hours. On Monday, a mid-level
ridge begins to build to the northeast of the tropical cyclone.
This should result in a slightly east of northward motion during
the next day or two. When the system moves into the northeast Gulf
of Mexico, a mid-level trough developing over the eastern United
states will likely cause Idalia to turn northeastward with an
increase in forward speed. The new official forecast is again
shifted slightly eastward, and is somewhat faster than the previous
one. This is a blend of the latest ECMWF and GFS solutions and is
also between the simple and corrected dynamical consensus tracks.

The intensity forecast is somewhat challenging. Idalia will be
traversing eastern Gulf of Mexico waters of high oceanic heat
content, and the environmental air mass should remain fairly moist.
The flow to the east of an upper-level trough could impart some
vertical wind shear over the system, but this shear could also be
compensated by the conducive effect of upper-level diffluence.
There is considerable spread in the model intensity guidance,
ranging from minimal to major hurricane status before landfall on
the northeast Gulf coast. The official intensity forecast is a
little higher than the previous one, and remains near the higher
end of the guidance. Given the uncertainties, users should monitor
future NHC forecasts for possible changes in the predicted strength
of Idalia, and prepare for possible significant impacts within the
hurricane and storm surge watch areas.


KEY MESSAGES:

1. Idalia is forecast to become a hurricane over the eastern Gulf of
Mexico, and there is an increasing risk of life-threatening storm
surge and hurricane-force winds along portions of the west coast of
Florida and the Florida Panhandle beginning as early as Tuesday.
Although it is too soon to specify the exact location and magnitude
of these impacts, residents in these areas should monitor updates to
the forecast and follow any advice given by local officials. Storm
surge and hurricane watches have been issued for portions of the
west coast of Florida and the coast of the Florida Panhandle, and
residents in these areas should monitor updates to the forecast and
follow any advice given by local officials.

2. Scattered flash and urban flooding can be expected across
portions of the west coast of Florida, the Florida Panhandle and
portions of the Southeast U.S. by Tuesday into Thursday. Flooding
from heavy rainfall is likely over portions of the southeast U.S. by
mid to late week.

3. Heavy rainfall from Tropical Storm Idalia is expected across
portions of the eastern Yucatan and western Cuba and may produce
areas of flash and urban flooding as well as landslides across
western Cuba.

4. Tropical storm conditions are expected over portions of the
Yucatan Peninsula and extreme western Cuba with tropical storm
conditions possible on the Isle of Youth.


FORECAST POSITIONS AND MAX WINDS

INIT 27/2100Z 20.1N 85.5W 35 KT 40 MPH
12H 28/0600Z 20.5N 85.3W 45 KT 50 MPH
24H 28/1800Z 21.7N 85.0W 55 KT 65 MPH
36H 29/0600Z 23.4N 84.9W 65 KT 75 MPH
48H 29/1800Z 25.6N 84.5W 75 KT 85 MPH
60H 30/0600Z 28.7N 83.7W 85 KT 100 MPH
72H 30/1800Z 31.3N 81.9W 50 KT 60 MPH...INLAND
96H 31/1800Z 34.5N 76.0W 50 KT 60 MPH...OVER WATER
120H 01/1800Z 35.0N 71.0W 55 KT 65 MPH

$$
Forecaster Pasch