225
WTNT41 KNHC 092056
TCDAT1

Hurricane Delta Discussion Number 21
NWS National Hurricane Center Miami FL AL262020
400 PM CDT Fri Oct 09 2020

Reports from an Air Force Reserve Hurricane Hunter aircraft and
WSR-88D Doppler radar data indicate that Delta has weakened some
more since the last advisory. The eye structure on the radar has
become less organized, with about 50 percent of the eyewall
remaining in the northern semicircle. The aircraft reported maximum
700-mb flight-level winds have decreased to the 100-105 kt range,
along with maximum SFMR surface wind estimates in the 80-85 kt
range. In addition, the central pressure has risen to near 966 mb.
Based on these data, the initial intensity is lowered to 90 kt.

The initial motion is now north-northeastward or 015/12 kt, with the
hurricane moving between a deep-layer ridge over the eastern Gulf of
Mexico and a mid- to upper-level trough over the U.S. Southern
Plains. This motion should continue through the next 24 h or so,
followed by a turn toward the northeast as Delta or its remnants
move along the southern edge of the mid-latitude westerlies. While
the track guidance remains tightly clustered, the guidance is a
little faster than the previous run. So, the new track forecast is
similar in direction, but slightly faster than the previous one.
The forecast track has the center of Delta making landfall in
southwestern Louisiana in the next few hours and then moving across
central and northeastern Louisiana tonight and Saturday morning.
After that, the system should move across northern Mississippi into
the Tennessee Valley before it dissipates.

Increasing vertical shear and decreasing oceanic heat content along
the forecast track could cause a little more weakening in the last
few hours before landfall. However, there will still be
significant impacts from winds and storm surge (see Key Messages
below). After landfall, rapid weakening is anticipated, with Delta
expected to weaken to a tropical storm tonight and to a tropical
depression by Saturday afternoon. As in the last advisory, the
cyclone is forecast to dissipate between 60-72 h based on the
consensus of the global models.

Key Messages:

1. Life-threatening storm surge is occurring and will continue near
and east of where Delta makes landfall this evening, and a Storm
Surge Warning is in effect from High Island, Texas, to the Mouth of
the Pearl River, Louisiana. The highest inundation of 7 to 11 feet
is expected somewhere between Rockefeller Wildlife Refuge and Morgan
City, Louisiana.

2. Hurricane-force winds are expected this afternoon and evening
within portions of the Hurricane Warning area, especially along the
coast of southwest Louisiana. Hurricane-force winds will also
spread inland across portions of southern Louisiana near the path of
Deltas center this evening and tonight.

3. Heavy rainfall will lead to significant flash flooding and minor
to major river flooding in parts of Louisiana today and Saturday.
Additional flooding is expected across portions of the central Gulf
Coast into the Lower Mississippi Valley.

FORECAST POSITIONS AND MAX WINDS

INIT 09/2100Z 29.3N 93.2W 90 KT 105 MPH
12H 10/0600Z 31.1N 92.5W 60 KT 70 MPH...INLAND
24H 10/1800Z 33.1N 91.0W 35 KT 40 MPH...INLAND
36H 11/0600Z 34.4N 89.2W 30 KT 35 MPH...INLAND
48H 11/1800Z 35.9N 87.1W 25 KT 30 MPH...INLAND
60H 12/0600Z 37.6N 84.8W 20 KT 25 MPH...POST-TROP/REMNT LOW
72H 12/1800Z...DISSIPATED

$$
Forecaster Beven
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