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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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