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Tropical Storm Darby Discussion Number  25
NWS Central Pacific Hurricane Center Honolulu HI   EP052022
500 AM HST Fri Jul 15 2022
 
Darby's satellite presentation has degraded further overnight and 
continues to be influenced by moderate west-southwesterly vertical 
wind shear of around 20 knots as indicated by UW-CIMSS vertical 
wind shear analysis, along with cool sea surface temperatures 
(SSTs) of around 25C shown in the NASA SPoRT SST composite. The 
latest subjective Dvorak current intensity estimates from 
PHFO/SAB/JTWC all came in at 4.0 (65 knots) while the UW-CIMSS 
objective ADT current intensity estimate was 3.1 (47 knots). 
Additionally, a SATCON estimate at 14/1046Z estimated the cyclones 
strength at 54 knots. Given the satellite degradation and 
incorporating a blend of the above intensity estimates, Darby's 
initial intensity has been lowered to 60 knots with this advisory, 
making the cyclone a tropical storm. Darby continues on its westward 
course, with the estimated initial motion set at 275/14 knots.

Darby will remain in a hostile environment during the next couple 
days, characterized by cool SSTs of 25-26C, moderate to strong 
westerly vertical wind shear of 20 to 30 knots, and surrounded by 
dry mid-level air with relative humidity values of less than 50 
percent. As a result, Darby is expected to continue to weaken 
quickly today, with a more steady decline thereafter through 
dissipation. The tropical cyclone is expected to weaken into a 
remnant low late Saturday or Saturday night, before dissipating on 
Sunday. The intensity forecast has been adjusted downward with 
this advisory package, and follows a blend of the dynamical and 
statistical intensity guidance.

The tropical cyclone will continue to be directed westward during 
the next couple days, influenced initially by a gradually building 
mid and upper level ridge to the north of the system, while deep 
convection persists. The cyclone will then begin to move slightly 
south of due west at a faster forward speed as deep convection 
becomes more sporadic, allowing Darby to be pushed along by the low 
level trade wind flow. The forecast track closely follows a blend 
of the latest GFS and ECMWF guidance (GFEX) through dissipation, 
and is essentially the same as the previous official forecast track.
 
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  15/1500Z 17.5N 146.1W   60 KT  70 MPH
 12H  16/0000Z 17.5N 148.5W   45 KT  50 MPH
 24H  16/1200Z 17.5N 152.0W   40 KT  45 MPH
 36H  17/0000Z 17.3N 155.9W   35 KT  40 MPH
 48H  17/1200Z 16.9N 159.8W   30 KT  35 MPH...POST-TROP/REMNT LOW
 60H  18/0000Z...DISSIPATED
 
$$
Forecaster Jelsema/Gibbs
 
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