ZCZC MIATCDAT4 ALL
TTAA00 KNHC DDHHMM CCA
 
Tropical Storm Ida Discussion Number   3...Corrected
NWS National Hurricane Center Miami FL       AL092021
1100 PM EDT Thu Aug 26 2021

Corrected Key Message Number 4

The Air Force Hurricane Hunters have been investigating Ida this 
evening and found maximum flight-level winds of 47 kt at 2500 ft. 
This data along with numerous unflagged 35-kt SFMR winds supported 
raising the intensity to 35 kt earlier this evening.  Since the 
aircraft departed Ida, there has been little change in the storm's 
structure, so the initial intensity was held at 35 kt.  Ida is an 
asymmetric tropical storm with most of the deep convection and 
stronger winds confined to the eastern half of the circulation. Both 
the NOAA and Air Force Hurricane Hunters will be investigating Ida 
Friday morning.
 
The storm has been wobbling around, but smoothing through the recent 
erratic motion yields an initial motion estimate of 320/10 kt. A 
mid-level ridge centered off the southeast U.S. coast is expected to 
shift westward on Friday and over 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 Friday 
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 GFS and ECMWF 
ensemble members basically span a similar region and are most 
concentrated across the state of Louisiana.  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 is some southwesterly vertical wind shear affecting Ida at the
moment, which is the likely part of the reason the cloud pattern and
wind field are asymmetric.  However, the global model show the
upper-level pattern becoming quite favorable late Friday and through
the weekend.  These more conducive winds aloft combined with very
warm SSTs and abundant moisture is likely to result in steady or
rapid intensification until Ida makes landfall in the U.S. The
intensity guidance unanimously show Ida becoming a hurricane, but
there is notable spread in how strong the system will become.  Given
the expected favorable environmental conditions for the storm, the
NHC intensity forecast lies near the high end of the model guidance,
in best agreement with the regional hurricane models.  It is also
worth noting that even though the global models are not particularly
accurate in predicting tropical cyclone winds, the GFS and ECMWF
show the minimum pressure falling more than 35 mb from the current
conditions.  Based on all of this information, there is
higher-than-normal confidence that a significant hurricane will be
approaching the Gulf coast late this weekend.
 
Key Messages:
 
1. Tropical storm conditions are expected in portions of the Cayman
Islands tonight and in portions of western Cuba and the Isle of
Youth Friday, 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 likely to produce heavy rainfall Sunday into Monday along
the central Gulf coast resulting in flash, urban, small stream, and
riverine flooding. 
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  27/0300Z 18.6N  80.5W   35 KT  40 MPH
 12H  27/1200Z 19.9N  82.0W   45 KT  50 MPH
 24H  28/0000Z 21.8N  83.9W   55 KT  65 MPH...NEAR CUBA
 36H  28/1200Z 23.8N  85.9W   65 KT  75 MPH
 48H  29/0000Z 25.6N  88.0W   75 KT  85 MPH
 60H  29/1200Z 27.3N  89.6W   85 KT 100 MPH
 72H  30/0000Z 29.0N  90.6W   95 KT 110 MPH...NEAR THE COAST
 96H  31/0000Z 32.0N  91.0W   45 KT  50 MPH...INLAND
120H  01/0000Z 33.9N  88.8W   25 KT  30 MPH...INLAND
 
$$
Forecaster Cangialosi
 
NNNN