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Hurricane Ida Discussion Number  14
NWS National Hurricane Center Miami FL       AL092021
1000 AM CDT Sun Aug 29 2021
 
Ida's rapid strengthening appears to have leveled off within the
past hour or so.  NOAA and Air Force Reserve Hurricane Hunter 
aircraft that have been in the storm this morning have reported 
peak flight-level winds of 146 to 148 kt between 8000 and
10000 ft, and believable SFMR winds around 130 kt.  Based on
these observations, the initial wind speed remains 130 kt for this
advisory. The central pressure appears to have bottomed out around  
929 mb, and the latest dropsonde in the eye from the Air Force 
plane supports a minimum pressure of 933 mb.  Ida's satellite and 
radar presentation is very impressive, as the 15-nm-wide eye is 
very well-defined and surrounded by a ring of intense convection.  
Within the past hour or so, there is evidence in radar imagery of a 
secondary eyewall, and this has likely caused Ida's intensity to 
level off for now.  Although Ida's extreme winds are confined to the 
inner eyewall, the aircraft data indicate that hurricane-force winds 
extend outward about 45 n mi to the northeast of the center, and 
based on buoy data the tropical-storm-force wind field extends 
outward about 130 n mi northeast of the center.
 
Ida's eyewall is nearing the coast of Louisiana, and any additional 
strengthening seems less likely now given the recent structural 
changes of the inner core.  While rapid weakening should occur after 
landfall, damaging winds will penetrate well inland across 
southeastern Louisiana and southwestern Mississippi through tonight. 
Ida is forecast to weaken to a tropical depression over Mississippi 
by late Tuesday.  The global model guidance now indicates that Ida 
will likely transition to an extratropical low when it nears the 
east coast of the United States and the new forecast shows the 
extratropical low becoming a gale center near Atlantic Canada at day 
5.
 
Ida has begun to slow down according to the latest aircraft and
radar fixes, and the initial motion estimate is 320/11 kt.  Ida's
forward speed is likely to slow further during the next 12 to 24 
hours as the hurricane turns north-northwestward, and then 
northward around the western periphery of a deep-layer ridge near
the southeastern United States coast.  The cyclone is predicted to
turn northeastward by late Tuesday ahead of a short-wave trough
that will move across the central United States.  The new NHC track 
is close to the HCCA corrected consensus and the GFS ensemble mean, 
and is not very different from the previous advisory. 
 
Key Messages:
 
1. Extremely life-threatening storm surge inundation of 9 feet or 
greater above ground level is imminent somewhere within the area 
from Burns Point, Louisiana, to Ocean Springs, Mississippi. 
Overtopping of local levees outside of the Hurricane and Storm 
Damage Risk Reduction System is possible where local inundation 
values may be higher.

2. Catastrophic wind damage will occur where the core of Ida moves 
onshore along the southeast coast of Louisiana in the next few 
hours. Hurricane-force winds and damaging wind gusts are expected 
today within the Hurricane Warning in southeastern Louisiana, 
including metropolitan New Orleans. 

3. Damaging winds, especially in gusts, will spread inland near the 
track of the center of Ida into southwestern Mississippi tonight 
and early Monday. These winds will likely lead to widespread tree 
damage and power outages.

4. Ida will continue to produce heavy rainfall today through Monday 
across the central Gulf Coast from southeast Louisiana, coastal 
Mississippi, and far southwestern Alabama, resulting in considerable 
to life-threatening flash and urban flooding and significant river 
flooding impacts. As Ida moves inland, significant flooding impacts 
are possible across portions of the Lower Mississippi, Tennessee 
Valley, Upper Ohio Valley, Central Appalachians and the Mid-Atlantic 
through Wednesday.

FORECAST POSITIONS AND MAX WINDS
 
INIT  29/1500Z 28.8N  90.0W  130 KT 150 MPH
 12H  30/0000Z 30.0N  90.8W   90 KT 105 MPH...INLAND
 24H  30/1200Z 31.6N  91.0W   50 KT  60 MPH...INLAND
 36H  31/0000Z 33.2N  90.3W   30 KT  35 MPH...INLAND
 48H  31/1200Z 34.9N  88.5W   25 KT  30 MPH...INLAND
 60H  01/0000Z 36.4N  85.9W   20 KT  25 MPH...INLAND
 72H  01/1200Z 37.8N  82.5W   20 KT  25 MPH...POST-TROP/INLAND
 96H  02/1200Z 40.5N  74.2W   30 KT  35 MPH...POST-TROP/EXTRATROP
120H  03/1200Z 43.5N  67.0W   35 KT  40 MPH...POST-TROP/EXTRATROP
 
$$
Forecaster Brown
 
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