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Hurricane IDA

Hurricane Ida Discussion Number   8
NWS National Hurricane Center Miami FL       AL092021
400 AM CDT Sat Aug 28 2021
Just after the last advisory, the convective structure of Ida got a
bit ragged, probably due to the residual effects of land
interaction with Cuba and a tongue of dry air that wrapped into the
eastern side of the circulation.  However, latest radar images from
Cuba show that the eye is becoming better defined, and satellite
imagery shows cooling of the cloud tops in the eyewall.  The
initial intensity has been held at 70 kt based on the latest trends
and earlier Hurricane Hunter aircraft data.  NOAA and Air Force
reserve Hurricane Hunter aircraft are scheduled to investigate Ida
again starting around 12Z.
The initial motion remains northwestward or 315/14.  A subtropical 
ridge centered off the southeast U.S. coast is expected to shift 
westward through the weekend, and this feature should continue to 
provide a steering flow that will take Ida steadily northwestward 
across the Gulf of Mexico during the next 36-48 h.  The track 
guidance remains in good agreement that Ida will make landfall on 
the coast of southeastern or central Louisiana late Sunday or early 
Monday morning.  After landfall, Ida is expected to turn northward 
through Louisiana and western Mississippi at a slower forward speed 
as it moves around the western end of the ridge.  Recurvature into 
the westerlies and an east-northeastward motion are expected by the 
end of the forecast period.  The new forecast track is nudged 
slightly to the west after 36 h to keep it near the various 
consensus models, but this is not a significant change from the 
previous forecast.  Users are again reminded to not focus on the 
exact details of the track forecast as storm surge, wind, and 
rainfall impacts will extend far from the center.
Ida is expected to remain in a favorable environment of light
vertical shear and very warm sea-surface temperatures until it
makes landfall.  The only negative factor is the possibility that
dry air may try to entrain into the system and slow the expected
intensification.  The SHIPS and LGEM models are showing a little
less strengthening than previously.  However, the HWRF and HMON
models continue to forecast Ida to reach Category 4 intensity
before landfall.  The new intensity forecast will forecast a peak
intensity of 120 kt in best agreement with the HWRF and HMON, and
the pre-landfall part of the forecast is little changed from the
previous forecast.  After landfall, rapid weakening is expected due
to land interaction, drier air, and an increase in shear, and Ida
is expected to become a post-tropical cyclone as it moves through
the Tennessee Valley.
As Ida continues to intensify over the Gulf of Mexico, an expansion
of its wind field is predicted. The NHC wind radii forecast is
largely based on the radii consensus, and winds of at least tropical
storm force are likely to reach the coast Sunday morning. Therefore,
all preparations to protect life and property for this dangerous
event need to be made today.
Key Messages:
1. Hurricane and tropical storm conditions are ending over Cuba.
However, Ida will continue to bring periods of heavy rain across
western Cuba through today that may lead to flash flooding and
2. There is a danger of life-threatening storm surge inundation
Sunday along the coasts of Louisiana and Mississippi within the
Storm Surge Warning area. Extremely life-threatening inundation of
10 to 15 feet above ground level is possible within the area from
Morgan City, Louisiana, to the Mouth of the Mississippi River.
Interests throughout the warning area should follow any advice given
by local officials.
3. Ida is expected to be an extremely dangerous major hurricane when
it reaches the coast of Louisiana. Hurricane-force winds are
expected Sunday in portions of the Hurricane Warning area along the
Louisiana coast, including metropolitan New Orleans, with
potentially catastrophic wind damage possible where the core of Ida
moves onshore. Actions to protect life and property should be rushed
to completion in the warning area.
4. Ida is likely to produce heavy rainfall later Sunday into Monday
across the central Gulf Coast from southeast Louisiana to coastal
Mississippi resulting in significant flash and riverine flooding
impacts. As Ida moves inland, flooding impacts are possible across
portions of the Lower Mississippi and Tennessee Valleys.
INIT  28/0900Z 24.0N  85.2W   70 KT  80 MPH
 12H  28/1800Z 25.4N  86.9W   85 KT 100 MPH
 24H  29/0600Z 27.1N  88.9W  105 KT 120 MPH
 36H  29/1800Z 28.6N  90.5W  120 KT 140 MPH
 48H  30/0600Z 30.1N  91.3W   85 KT 100 MPH...INLAND
 60H  30/1800Z 31.6N  91.2W   45 KT  50 MPH...INLAND
 72H  31/0600Z 33.2N  90.5W   30 KT  35 MPH...INLAND
 96H  01/0600Z 36.0N  87.0W   25 KT  30 MPH...INLAND
120H  02/0600Z 37.5N  82.5W   20 KT  25 MPH...POST-TROP/REMNT LOW
Forecaster Beven