Tropical Storm IDA Advisory 8月30日

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Hurricane Ida Discussion Number  15
NWS National Hurricane Center Miami FL       AL092021
400 PM CDT Sun Aug 29 2021

NWS Doppler radar imagery and data from an Air Force Reserve
Reserve Hurricane Hunter aircraft showed that Ida made landfall
around 1655 UTC along the southeastern coast of Louisiana near
Port Fourchon with estimated maximum winds of 130 kt and a minimum
pressure around 930 mb.  Since that time, Ida made a second
landfall southwest of Galliano, Louisiana, and with the eyewall now
onshore weakening has begun.  Based on the latest Doppler
velocities the initial wind speed has been conservatively reduced
to 115 kt for this advisory.  As Ida's circulation moves farther
inland this evening and overnight a faster rate of weakening is
expected, and Ida is forecast to become a tropical depression over
Mississippi by late Monday.  Although weakening is forecast,
damaging winds, especially in gusts, are expected to spread inland
over southeastern Louisiana and southwestern Mississippi through
Monday morning.  To account for this, the gust factor in the
Forecast/Advisory has been adjusted accordingly.  By 72 hours, Ida
is predicted to merge with a frontal zone over the eastern United
States and become an extratropical low, and this low is forecast to
strengthen into a gale center near Atlantic Canada by the end of
the forecast period.

Radar fixes indicate that Ida's forward motion has slowed and the
initial motion estimate is 325/9 kt.  The hurricane should turn
northward tonight around the western periphery of a deep-layer
ridge near the southeastern United States coast.  Ida is forecast
to turn northeastward and recurve over the eastern United States as
it enters the mid-latitude westerlies.  The GFS is a bit faster in
ejecting the post-tropical cyclone northeastward on days 3 through
5, and the NHC forecast follows a blend of the various consensus
models and the GFS ensemble mean.

Key Messages:

1. Extremely life-threatening storm surge inundation of 9 feet or
greater above ground level will continue through early this
evening along portions of the coast between 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 near the core of Ida as
it moves inland over southeastern Louisiana during the next few
hours.  Hurricane-force winds and damaging wind gusts are expected
through tonight within the Hurricane Warning area 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 through Monday across
the central Gulf Coast across southeast Louisiana, coastal
Mississippi, and 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
Valley, Tennessee Valley, Upper Ohio Valley, Central Appalachians,
and Mid-Atlantic through Wednesday.

FORECAST POSITIONS AND MAX WINDS

INIT  29/2100Z 29.5N  90.6W  115 KT 130 MPH...INLAND
 12H  30/0600Z 30.7N  90.9W   65 KT  75 MPH...INLAND
 24H  30/1800Z 32.4N  90.7W   35 KT  40 MPH...INLAND
 36H  31/0600Z 34.0N  89.4W   25 KT  30 MPH...INLAND
 48H  31/1800Z 35.6N  87.2W   25 KT  30 MPH...INLAND
 60H  01/0600Z 37.1N  84.2W   20 KT  25 MPH...POST-TROP/INLAND
 72H  01/1800Z 38.6N  80.5W   20 KT  25 MPH...POST-TROP/EXTRATROP
 96H  02/1800Z 41.3N  72.5W   30 KT  35 MPH...POST-TROP/EXTRATROP
120H  03/1800Z 43.8N  67.0W   35 KT  40 MPH...POST-TROP/EXTRATROP

$$
Forecaster Brown