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Hurricane IDA

Hurricane Ida Discussion Number  10
NWS National Hurricane Center Miami FL       AL092021
400 PM CDT Sat Aug 28 2021
Ida's satellite presentation has continued to improve this
afternoon, with the eye becoming more apparent in both infrared and
visible satellite imagery.  The eye is surrounded by a symmetric
ring of cold cloud tops and new convection with lightning as seen
by the GOES-16 GLM sensor has been rotating around the western 
portion of the eyewall within the past few hours. The upper-level 
outflow has also become well established over the hurricane and 
several spiral bands are noted over the northern semicircle.  
Subjective Dvorak satellite intensity estimates have increased to 
T5.0 and these support increasing the initial intensity to 90 kt 
for this advisory.  Both NOAA and Air Force Reserve reconnaissance 
aircraft are scheduled to be in the hurricane within the next few 
hours and should provide additional information on Ida's current 
strength. Earlier aircraft and satellite wind data indicate that the 
tropical-storm-force wind field has continued to expand over the 
eastern semicircle and the initial wind radii have been adjusted 
The hurricane appears to have begun its anticipated rapid 
intensification phase.  A favorable upper-level wind pattern, warm 
waters along the track, and a moist atmosphere are expected to allow 
for additional rapid strengthening overnight and early Sunday.  This 
is again supported by the majority of the intensity models, and the 
NHC wind speed forecast continues to call for rapid strengthening, 
bringing Ida to Category 4 status within 12 to 18 hours.  An eyewall 
replacement cycle could occur as Ida nears the northern Gulf coast, 
so some fluctuations in intensity are possible during that time.  
After landfall, rapid weakening is expected, and Ida is forecast to 
become a post-tropical cyclone by day 4, and it is likely to be 
absorbed along a frontal zone by day 5.
Ida has moved a little to the right of the previous track, but the 
long-term motion motion is still northwestward or 320/14 kt.  The 
track forecast philosophy remains unchanged.  Ida is expected to 
continue on a northwestward heading through late Sunday as it is 
steered around the southwestern portion of a deep-layer ridge near 
the southeastern United Stated coast.  After landfall, Ida's forward 
motion is forecast to slow when it turns northward around the 
western extent of the aforementioned ridge.  By Tuesday, the cyclone 
should reach the southern extent of the mid-latitude westerlies, 
causing it to turn north-northeastward across the Lower Mississippi 
and Tennessee Valleys.  The track guidance has nudged slightly 
eastward during the first 12-24 hours, primarily due to the more 
northeastward initial position, and this has required a slight 
rightward adjustment in the new official forecast at those times.  
The remainder of the NHC forecast is largely unchanged from before, 
and lies near various consensus models and the GFS ensemble mean.
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.  Rainfall impacts will also spread 
inland across the Lower Mississippi and Tennessee Valleys through 
early next week after Ida makes landfall.
Key Messages:

1. There is a danger of life-threatening storm surge inundation 
Sunday along the coasts of Louisiana, Mississippi, and Alabama  
within the Storm Surge Warning area. Extremely life-threatening 
inundation of 9 feet or greater above ground level is possible 
somewhere within the area from Morgan City, Louisiana, to the coast 
of Mississippi. Overtopping of local levees outside of the Hurricane 
and Storm Damage Risk Reduction System is possible where local 
inundation values may be higher. Interests throughout the warning 
area should follow any advice given by local officials.
2. 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.
3. Damaging winds, especially in gusts, will spread inland near the
track of the center of Ida across portions of southeastern Louisiana
and southwestern Mississippi Sunday night and early Monday. These
winds will likely lead to widespread tree damage and power outages.
4. Ida is likely to produce heavy rainfall Sunday into 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, 
and Ohio Valleys through Wednesday.
INIT  28/2100Z 26.2N  87.0W   90 KT 105 MPH
 12H  29/0600Z 27.5N  88.6W  110 KT 125 MPH
 24H  29/1800Z 29.1N  90.4W  115 KT 130 MPH
 36H  30/0600Z 30.5N  91.3W   65 KT  75 MPH...INLAND
 48H  30/1800Z 32.2N  91.2W   35 KT  40 MPH...INLAND
 60H  31/0600Z 34.0N  90.1W   25 KT  30 MPH...INLAND
 72H  31/1800Z 35.7N  88.1W   20 KT  25 MPH...INLAND
 96H  01/1800Z 38.0N  82.5W   20 KT  25 MPH...POST-TROP/INLAND
120H  02/1800Z...DISSIPATED
Forecaster Brown