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Hurricane Ida Discussion Number   6
NWS National Hurricane Center Miami FL       AL092021
500 PM EDT Fri Aug 27 2021
 
Cuban radar data and reports from an earlier Air Force Reserve 
Hurricane Hunter mission indicate that Ida's inner core structure 
continued to improve after the release of the previous advisory 
package.  An eye became apparent in radar imagery before the center 
reached the Isle of Youth, and the final fix from the Air Force 
Hurricane Hunter aircraft reported a closed 24-n-mi wide eye.  The 
aircraft measured winds to support hurricane intensity shortly 
before 1800 UTC, and during the final northeast eyewall pass, and 
flight-level wind data support increasing the intensity to 70 kt, 
which is used as the initial intensity for this advisory.
 
The upper-level outflow has expanded over all but the southwestern
portion of the circulation, and the upper-level wind pattern is
forecast to continue to improve overnight and early Saturday.
Once Ida moves past western Cuba and into the southeastern Gulf of
Mexico, it will be moving through a very favorable oceanic and
atmospheric environment consisting of high ocean heat content
waters, low vertical wind shear, and a moist low- to mid-level
atmosphere.  These conditions are likely to result in a period
of rapid strengthening during the next 24 to 36 hours.  In fact,
with the higher initial wind speed, the intensity guidance has
significantly increased this cycle, and the bulk of the guidance
now brings Ida to category 4 intensity.  The NHC forecast explicitly
calls for rapid intensification during the next 24 to 36 hours,
which is supported by several of the dynamical models, the LGEM
model, and high probabilities of rapid intensification indicated
by the SHIPS and DTOPS RI guidance.  The NHC forecast is near
the IVCN multi-model consensus aid, but is lower than HCCA and
LGEM.  It should be noted that some fluctuations in intensity are 
possible as Ida nears the northern Gulf coast due to possible 
eyewall replacement cycles.  In addition to the expected increase in 
strength, the dynamical model guidance again calls for Ida's wind 
field to expand while it moves over the Gulf of Mexico.  As a 
result, there is higher-than-normal confidence that a large and 
powerful hurricane will impact portions of the northern Gulf coast 
by late this weekend and early next week.
 
Ida has wobbled a little right of the previous track, but the longer
term motion continues to be northwestward or 320/13 kt. The steering 
currents remain well-established as a strong deep-layer ridge over 
the western Atlantic should continue to steer Ida northwestward 
across the Gulf this weekend.  Ida will approach the western 
portion of the ridge after landfall, and this should result in a 
slower northward motion by day 3.  After that time, a short-wave 
trough over the central United States is expected to cause the 
system to turn northeastward.  The track guidance remains in 
remarkably good agreement through landfall along the northern Gulf 
coast, and there is higher-than-normal confidence in that portion of 
the track forecast.  However, 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.
 
Key Messages:
 
1. Life-threatening storm surge and hurricane conditions are 
expected to continue through tonight in portions of western Cuba, 
including the Isle of Youth, where a Hurricane Warning is in effect. 
Life-threatening heavy rains, flash flooding and mudslides are 
expected across Jamaica, the Cayman Islands, and western Cuba, 
including the Isle of Youth.

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 and Alabama, resulting in considerable flash, urban, 
small stream, and riverine flooding impacts. As Ida moves inland, 
flooding impacts are possible across portions of the Lower 
Mississippi and Tennessee Valleys.
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  27/2100Z 22.1N  83.2W   70 KT  80 MPH
 12H  28/0600Z 23.5N  84.8W   85 KT 100 MPH
 24H  28/1800Z 25.3N  86.9W  105 KT 120 MPH
 36H  29/0600Z 27.1N  89.0W  115 KT 130 MPH
 48H  29/1800Z 28.6N  90.6W  120 KT 140 MPH
 60H  30/0600Z 30.0N  91.3W   80 KT  90 MPH...INLAND
 72H  30/1800Z 31.5N  91.1W   40 KT  45 MPH...INLAND
 96H  31/1800Z 34.4N  89.3W   30 KT  35 MPH...INLAND
120H  01/1800Z 36.0N  86.0W   20 KT  25 MPH...POST-TROP/REMNT LOW
 
$$
Forecaster Brown
 
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