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Hurricane Darby Discussion Number   9
NWS National Hurricane Center Miami FL       EP052022
500 AM HST Mon Jul 11 2022
 
What a difference 24 hours makes! Darby has been rapidly 
intensifying for the last 12-18 hours, with the eye continuing to 
clear out on GOES-17 infrared satellite imagery surrounded by a 
thick ring of cold -65 to -75C cloud top temperatures. It is clear 
that the tropical cyclone was able to mix out the remaining dry air 
near its center last night and the last several microwave passes 
from GMI at 0732 UTC and AMSR2 at 0959 UTC have an impressive 
presentation with a thick ring of eyewall convection on the 89-GHz 
channel. Subjective Dvorak satellite estimates from TAFB and SAB are 
constrained due to Dvorak rules, but their data-T numbers were both 
T5.5/102 kt. The most recent CI number from the UW-CIMSS objective 
Advanced Dvorak Technique (ADT) was at T6.0/115 kt. Favoring the 
higher ADT estimate more, the current intensity is set to 110 kt, 
though this could be conservative.
 
There are no obvious signs currently that would prevent Darby from 
intensifying further. There are few indications that an eyewall 
replacement cycle is imminent from the earlier microwave imagery and 
SHIPS guidance indicates the storm remains in a very low shear 
(near 5 kt) environment and over sufficently warm sea-surface 
temperatures (27-28 C). Thus, rapid intensification is forecast to 
continue over the next 12 h, and the NHC foreast intensity peaks 
Darby at 120 kt, which matches the latest ECMWF- and GFS-based 
SHIPS which have correctly been on the high side of the guidance 
envelope. After 36 hours, Darby is expected to move into sub 26C 
SSTs, and westerly shear is forecast to increase between 48-72 
hours. Thus, the small vortex of Darby could weaken rapidly after 36 
hours, with the latest intensity forecast still making the system a 
post-tropical cyclone at the end of the forecast period.
 
Darby is continuing westward along at the same general speed and 
heading at 270/13 kt, steered primarily by a mid-level ridge 
centered to its north. The hurricane is expected to approach a 
slight weakness in the ridge after 24 hours, allowing the cyclone to 
gradually shift to a more west-northwestward track between 36-72 
hours. However, by the end of the forecast period, as Darby becomes 
shallow vortex, its track will likely bend back westward as the 
low-level trade wind flow becomes dominant. The latest track 
forecast is not all that different from the previous one, choosing 
to remain close to a consensus of the GFS and ECMWF forecasts (GEFX) 
which remains just a bit north of the consensus aids HCCA and TVCE, 
which are influenced by the further south tracks of the weaker 
HWRF/HMON/UKMET guidance.
 
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  11/1500Z 14.6N 123.4W  110 KT 125 MPH
 12H  12/0000Z 14.7N 125.6W  120 KT 140 MPH
 24H  12/1200Z 14.8N 128.1W  120 KT 140 MPH
 36H  13/0000Z 15.0N 130.5W  105 KT 120 MPH
 48H  13/1200Z 15.4N 133.2W   85 KT 100 MPH
 60H  14/0000Z 15.9N 135.8W   70 KT  80 MPH
 72H  14/1200Z 16.7N 138.5W   55 KT  65 MPH
 96H  15/1200Z 17.5N 143.3W   35 KT  40 MPH
120H  16/1200Z 17.3N 149.0W   30 KT  35 MPH...POST-TROP/REMNT LOW
 
$$
Forecaster Papin
 
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