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Tropical Storm Delta Discussion Number   4
NWS National Hurricane Center Miami FL       AL262020
1100 AM EDT Mon Oct 05 2020
 
The convective structure of Delta has continued to improve this 
morning.  Earlier microwave data and early-light visible satellite 
imagery showed that the center of the tropical cyclone re-formed 
farther south within the area of deep convection.  Since that time, 
banding has continued to increase around the southern and eastern 
portion of the circulation, and a small CDO-like feature has formed. 
 The intensity has been set at 40 kt, which is a blend of the 
subjective Dvorak estimate from TAFB and objective satellite 
intensity estimates from UW/CIMSS.  A NOAA Hurricane Hunter aircraft 
is scheduled to investigate the tropical storm this afternoon, which 
should provide a better assessment of the cyclone's intensity, 
structure, and wind field.
 
With the earlier center re-formation, the initial motion estimate is 
a somewhat uncertain 280/6 kt.  Delta is expected to resume a 
west-northwestward motion later today.  A northwestward heading 
around the southwestern portion of a deep-layer ridge should begin 
tonight or Tuesday, and that general motion with some increase in 
forward speed is expected to continue through 60-72 hours.  After 
that time, a broad mid- to upper-level trough is forecast to develop 
over the south-central United States, which should weaken the 
western portion of the ridge and cause Delta to turn northward 
toward the northern Gulf Coast.  After day 4, Delta should begin to 
accelerate north-northeastward or northeastward ahead of the 
aforementioned trough.  The new NHC track forecast has been adjusted 
to the south and west of the previous advisory during the first 
couple of days, primarily due to the recent center re-formation and 
more southward initial position. After that time, the NHC track is 
not much different than the previous forecast and lies near the 
center of the tightly clustered dynamical model envelope.
 
Delta is forecast to traverse very warm waters over the northwestern 
Caribbean Sea and be in a very low vertical wind shear environment 
during the next couple of days.  These conditions should allow for 
significant strengthening during that time, and the NHC intensity 
forecast is at or above the various intensity aids.  It is somewhat 
surprising that the intensity aids were generally a little lower 
this cycle, but the expected low shear and SHIPS rapid 
intensification index support the higher than climatological rate 
of intensification.  After 72 hours, increasing southwesterly shear 
and the cooler shelf waters over the northern Gulf are likely to 
induce some weakening later in the period.  The updated NHC 
intensity forecast calls for a faster rate of intensification over 
the next 48-60 hours, but is similar to the previous advisory 
thereafter.
 
Key Messages:
 
1. Tropical storm conditions are expected in the Cayman Islands
beginning late today or tonight, and a Tropical Storm Warning is
in effect.
 
2. Dangerous storm surge and hurricane conditions are expected in 
portions of western Cuba by Tuesday afternoon, and a Hurricane 
Warning is in effect.
 
3. Heavy rainfall will affect portions of Jamaica, the Cayman 
Islands, and western Cuba during the next few days. This rainfall 
could lead to significant flash flooding and mudslides. 
 
4. Delta is forecast to approach the northern Gulf Coast late this 
week as a hurricane. While there is large uncertainty in the track 
and intensity forecasts at these time ranges, there is an increasing 
risk of dangerous storm surge, wind, and rainfall hazards along the 
coast from Louisiana to the western Florida Panhandle. Residents in 
these areas should monitor the progress of Delta and check for 
updates to the forecast during the week.
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  05/1500Z 16.4N  78.6W   40 KT  45 MPH
 12H  06/0000Z 17.1N  79.6W   50 KT  60 MPH
 24H  06/1200Z 18.7N  81.7W   60 KT  70 MPH
 36H  07/0000Z 20.8N  84.3W   75 KT  85 MPH
 48H  07/1200Z 22.8N  86.8W   85 KT 100 MPH
 60H  08/0000Z 24.6N  89.1W   90 KT 105 MPH
 72H  08/1200Z 26.0N  90.7W   90 KT 105 MPH
 96H  09/1200Z 28.8N  91.1W   85 KT 100 MPH
120H  10/1200Z 33.1N  88.2W   40 KT  45 MPH...INLAND
 
$$
Forecaster Brown
 
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