ZCZC MIATCDAT4 ALL
TTAA00 KNHC DDHHMM
 
Tropical Storm Ida Discussion Number   5
NWS National Hurricane Center Miami FL       AL092021
1100 AM EDT Fri Aug 27 2021
 
Radar imagery from Grand Cayman and Cuba as well as satellite data
continue to show an improvement in Ida's overall structure this
morning, with an increase in banding, the development of a small
central dense overcast, and more recently an improved inner-core 
feature. Both the NOAA and Air Force reconnaissance aircraft 
reported that the pressure has fallen to around 996 mb, and the Air 
Force plane has measured flight-level and SFMR winds that support 
an initial intensity of 55 kt. 
 
Although there is still some southwesterly shear over Ida, the
outflow has begun to expand over the northeastern and southeastern
portions of the circulation.  The upper-level trough near the
Yucatan peninsula that has been imparting the shear over Ida is
forecast to weaken and move westward during the next 12 to 24
hours, which should result in a more favorable upper-level
wind pattern.  This, in combination with warm sea surface 
temperatures and a moist environment along the forecast track of
the storm are expected to result in steady to rapid strengthening.
Ida is now foreast to become a hurricane when it is near western
Cuba and once it moves over the southeastern Gulf of Mexico a period 
of rapid strengthening is likely to begin, with the NHC intensity 
forecast explicitly calling for rapid intensification to major 
hurricane strength between 24 and 48 hours.  The official intensity 
forecast is on the higher side of the intensity guidance but not 
quite as high as the slightly more aggressive CTCI, HWRF, and HCCA 
models.  In addition to the increase in strength, the dynamical 
model guidance indicates that Ida's wind field will grow larger as 
it moves over the Gulf of Mexico and this is reflected in the NHC 
wind radii forecast.  In summary, there is a higher-than-normal 
confidence that a significant hurricane will impact a large portion 
of the northern Gulf coast by late this weekend and early next week.
 
Ida is moving northwestward or 320/13 kt. The track forecast
reasoning is unchanged from before.  A mid-level ridge over the
western Atlantic is forecast to move westward and this should keep
Ida on a general northwestward heading during the next 48-60 hours.
This track will bring the storm across western Cuba later today, 
over the southeastern and central Gulf of Mexico on Saturday and
Saturday night, to the coast of Louisiana by late Sunday. The
track guidance is in remarkably good agreement with very little
cross-track spread during the first 60 hours or so of the forecast
period.  After that time, Ida is forecast to reach the western
portion of the ridge, which is expected to cause the storm to slow
down and turn northward and then northeastward over the 
southeastern United States.  The NHC track forecast is near or
just east of the various consensus aids, in best agreement with the 
GFS ensemble mean.  Although the small spread in the guidance 
through landfall increases the overall confidence in the track 
forecast, users are reminded to not focus on the exact details of 
the forecast track 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 later today and 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. The risk of life-threatening storm surge inundation is increasing
along the coasts of Louisiana, Mississippi, and Alabama. Inundation
of 7 to 11 feet above ground level is possible within the area from
Morgan City, Louisiana, to Ocean Springs, Mississippi, including
Lake Borgne. Interests in these areas should follow any advice given
by local officials.
 
3. Ida is expected to be a dangerous major hurricane when it reaches
the northern Gulf Coast on Sunday, and the risk of hurricane-force
winds continues to increase, especially along portions of the
Louisiana coast, including metropolitan New Orleans. Potentially
devastating wind damage could occur where the core of Ida moves
onshore.
 
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, as well as the Lower Mississippi Valley,
resulting in considerable flash, urban, small stream, and riverine
flooding.

FORECAST POSITIONS AND MAX WINDS
 
INIT  27/1500Z 20.7N  82.1W   55 KT  65 MPH
 12H  28/0000Z 22.2N  83.7W   65 KT  75 MPH...OVER WESTERN CUBA
 24H  28/1200Z 24.0N  85.8W   75 KT  85 MPH...OVER WATER
 36H  29/0000Z 25.9N  87.8W   90 KT 105 MPH
 48H  29/1200Z 27.6N  89.7W  105 KT 120 MPH
 60H  30/0000Z 29.0N  90.8W  105 KT 120 MPH
 72H  30/1200Z 30.3N  91.3W   60 KT  70 MPH...INLAND
 96H  31/1200Z 33.3N  90.2W   30 KT  35 MPH...INLAND
120H  01/1200Z 35.2N  87.1W   20 KT  25 MPH...POST-TROP/REMNT LOW
 
$$
Forecaster Brown
 
NNNN