000 WTPA41 PHFO 151436 TCDCP1 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