Official Discussion issued by the National Hurricane Center

Delta (AL262020) DATA RELEASED: 10/6/2020 9:00:00 PM UTC

Copy of official data

Hurricane Delta Discussion Number   9
NWS National Hurricane Center Miami FL       AL262020
500 PM EDT Tue Oct 06 2020

Shortly after the release of the 1500 UTC advisory package, the
NOAA Hurricane Hunter aircraft measured a peak flight-level wind
of 132 kt, and during its final passage through the northeast
eyewall around 1700 UTC it reported a peak SFMR wind of 121 kt.
The aircraft continued to report an extremely small 4-to-5-nmi-wide
eye. The central pressure did level off somewhat on the final
couple of penetrations, with the latest reported central pressure 
at 956 mb.  The initial wind speed was raised to 120 kt on the 
earlier intermediate advisory, and has been set at 125 kt for this 
advisory.  The next reconnaissance aircraft mission into the 
hurricane is scheduled for this evening.

There has been no evidence of an outer eyewall from the aircraft
reports or earlier radar imagery from Grand Cayman. As a 
result, some additional strengthening is likely to occur before 
Delta reaches the northeastern coast of the Yucatan peninsula late
tonight or early Wednesday.  The NHC intensity forecast is once 
again a little above the various intensity aids until landfall in 
Mexico.  When the small inner core of Delta moves over land, 
weakening is expected, but warm waters and low vertical wind shear 
over the southern Gulf of Mexico should support re-strengthening, 
and a second peak in intensity is likely when Delta is over the 
central Gulf of Mexico in 48-60 hours.  After that time, increasing
southwesterly shear and the cooler shelf waters over the 
northern Gulf are expected to cause some reduction in wind speed.  
The global models, however, depict a significant increase in the 
size of Delta's wind field while it is over the Gulf of Mexico,  
which increases the spatial extent of the storm surge and wind 
threats for the northern Gulf coast.  So regardless of Delta's 
final landfall intensity, the projected large size of the hurricane 
is likely to result in a significant storm surge and wind event for 
portions of the northern Gulf coast later this week.

Delta has been moving steadily west-northwestward today at 300/15 
kt. The track forecast reasoning remains unchanged from the previous 
advisory.  A mid-level ridge over Florida and the northeastern Gulf 
of Mexico is expected to continue steering Delta west-northwestward 
during the next 36-48 hours.  After that time, a developing trough 
over the south-central United States should cause Delta to turn 
northward, and by Friday the hurricane is forecast to begin 
accelerating northward or north-northeastward ahead of the trough.  
This motion will bring Delta onshore along the northern Gulf coast 
between 72 and 96 hours.  The dynamical models continue to be 
tightly clustered through 48-72 hours with some increase in spread 
thereafter.  The overall trend in the guidance has been slightly 
westward, and the new forecast has been adjusted accordingly and 
lies near the middle of the envelope. Supplemental upper-air balloon 
launches at 0600 and 1800 UTC have begun at upper-air sites across 
portions of the southeastern United States.  In addition, a NOAA 
G-IV synoptic surveillance mission is in progress and should provide 
additional data for the 0000 UTC cycle of the dynamical models. 

Key Messages:

1. Life-threatening storm surge and potentially catastrophic wind 
damage are expected within portions of the northern Yucatan 
Peninsula of Mexico beginning tonight. All preparations to protect 
life and property should be rushed to completion. 

2. Heavy rainfall will affect portions of the Cayman Islands, 
western Cuba and the northern Yucatan Peninsula through midweek. 
This rainfall could lead to significant flash flooding and 
mudslides. The potential for heavy rain, flash and possible minor 
river flooding will increase across portions of the central Gulf 
Coast, Tennessee Valley, and southeastern United States as Delta 
moves inland later this week.

3. There is an increasing likelihood of life-threatening storm surge 
and dangerous hurricane-force winds, especially along the coasts of 
Louisiana and Mississippi, beginning on Friday. Residents in these 
areas should ensure they have their hurricane plan in place and 
follow advice given by local officials.  Storm surge and hurricane 
watches will likely be issued for portions of the northern Gulf 
Coast on Wednesday. 


INIT  06/2100Z 18.9N  84.1W  125 KT 145 MPH
12H  07/0600Z 20.2N  86.1W  135 KT 155 MPH
24H  07/1800Z 21.8N  88.8W  105 KT 120 MPH
36H  08/0600Z 23.0N  91.1W  110 KT 125 MPH
48H  08/1800Z 24.4N  92.6W  115 KT 130 MPH
60H  09/0600Z 25.9N  93.2W  115 KT 130 MPH
72H  09/1800Z 28.0N  92.9W  110 KT 125 MPH
96H  10/1800Z 32.4N  90.9W   55 KT  65 MPH...INLAND
120H  11/1800Z 35.5N  87.3W   20 KT  25 MPH...POST-TROP/REMNT LOW

Forecaster Brown