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Tropical Storm Ida Discussion Number   4
NWS National Hurricane Center Miami FL       AL092021
500 AM EDT Fri Aug 27 2021
 
Radar data from Grand Cayman and satellite imagery indicate that Ida 
is becoming better organized just to the north of Grand Cayman. The 
convection has become more concentrated near the center, and the 
radar data is showing increasing curved banding.  In addition, the 
pressure at Grand Cayman fell to 1003 mb, showing that the central 
pressure is lower than observed by the aircraft mission yesterday 
afternoon.  Based on a combination of the Grand Cayman observations 
and satellite intensity estimates from TAFB and SAB, the initial 
intensity is increased to 40 kt.  Air Force Reserve and NOAA 
Hurricane Hunter aircraft are scheduled to investigate Ida near 12Z.
 
After the earlier wobbling, Ida seems to have resumed a
northwestward motion of 320/13.  A mid-level ridge centered off the
southeast U.S. coast is expected to shift westward through the
weekend.  This feature should keep Ida moving on a general
northwestward track for the next 2 or 3 days, taking the core of
the system over western Cuba this afternoon or evening and then
across the southern and central Gulf of Mexico this weekend.
Although some model timing differences remain, they are in fairly
good agreement that Ida will make landfall in Louisiana late Sunday
or early Monday.  The new forecast track is shifted a little to the
east of the previous forecast through 48 h based on the initial
location.  However, the 60 and 72 h positions are similar to the
previous forecast, and thus there is no significant change to the
forecast landfall area in Louisiana at this time.  Users are
reminded to not focus on the exact forecast track as impacts will
extend far from the center and the average 72-hour track error is
around 120 miles.
 
There continues to be some southwesterly shear affecting Ida due to 
the storm's location between an upper-level trough to the west and 
an upper-level anticyclone to the east.  Some decrease in the shear 
is expected during the next 24 h, and that, combined with a moist 
environment and warm sea surface temperatures along the forecast 
track, should allow steady to rapid strengthening until the cyclone 
makes landfall along the northern Gulf coast.  The new intensity 
forecast is slightly stronger than the previous forecast, and it now 
calls for Ida to reach a peak intensity of 100 kt before landfall.  
It should be noted that this intensity is lower than that forecast 
by the HMON model, the HCCA corrected consensus model, and the 
Florida State Superensemble.  After landfall, Ida should weaken as 
it moves through the lower Mississippi and Tennessee River valleys.  
Based on the available guidance, there remains higher-than-normal 
confidence that a significant hurricane will approach and impact the 
Gulf coast during the weekend and early next week.
 
 
Key Messages:
 
1. Tropical storm conditions are occurring in portions of the Cayman
Islands, and they are expected in portions of western Cuba and the
Isle of Youth today, where a dangerous storm surge is also possible
in areas of onshore flow. 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 an increasing risk of life-threatening storm surge
inundation along the coasts of Louisiana, Mississippi, and Alabama,
where a Storm Surge Watch is in effect. Interests in these areas
should follow any advice given by local officials.
 
3. There is an increasing risk of dangerous hurricane-force winds
beginning Sunday along the portions of the coasts of Louisiana and
Mississippi, including metropolitan New Orleans, where a Hurricane
Watch is in effect.
 
4. Ida is also expected to produce heavy rains across the central 
Gulf Coast from southeast Louisiana to coastal Mississippi, Alabama, 
as well as the Lower Mississippi Valley starting Sunday into Monday, 
resulting in considerable flash, urban, small stream, and riverine 
flooding.
 
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  27/0900Z 20.0N  81.4W   40 KT  45 MPH
 12H  27/1800Z 21.5N  82.9W   50 KT  60 MPH...OVER ISLE OF YOUTH
 24H  28/0600Z 23.4N  84.9W   60 KT  70 MPH
 36H  28/1800Z 25.3N  86.9W   70 KT  80 MPH
 48H  29/0600Z 27.1N  88.8W   85 KT 100 MPH
 60H  29/1800Z 28.7N  90.2W  100 KT 115 MPH
 72H  30/0600Z 30.1N  91.1W   85 KT 100 MPH...INLAND
 96H  31/0600Z 33.0N  90.5W   35 KT  40 MPH...INLAND
120H  01/0600Z 35.0N  88.0W   25 KT  30 MPH...INLAND
 
$$
Forecaster Beven
 
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