Central Pacific Basin Tropical Cyclones

Tropical Storm Darby Forecast Discussion

WTPA41 PHFO 160234

Tropical Storm Darby Discussion Number  27
NWS Central Pacific Hurricane Center Honolulu HI   EP052022
500 PM HST Fri Jul 15 2022

The UW-CIMSS shear analysis near Darby shows that the westerly 
shear over the system has actually relaxed just a bit, now only 
around 20 kt. This may have been enough for a brief burst of deep 
convection in the northwest quadrant this afternoon. That convection 
has since dissipated, however, and the last persistent deep 
convection was about 1400Z. An earlier 1914Z ASCAT-B pass showed 
three wind barbs of 40-41 kt on the north side of the center. 
Various Dvorak intensity estimates ranged from 45 kt at PHFO to 33 
KT from the UW-CIMSS ADT. CIMSS SATCON from 0050Z had a CI of 37 kt. 
Based on a blend of these estimates, have gone with an initial 
intensity of 40 kt.

The initial motion is 275/14. A large anticyclone far north of 
Darby in both the mid- and low-levels will maintain a westerly track 
over the next few days. The current forecast track remains close to 
the past track, near the center of the guidance. 

The forecast track keeps Darby in a moderately sheared environment 
for the next couple of days, and over sea surface temperatures 
(SST) of 25-26C. The shear, SST and climatologically meager  
mid-level relative humidity values near the track all work against 
persistent deep convection redeveloping with Darby, although the 
simulated satellite imagery from the GFS and ECMWF both show brief 
bursts from time to time. A strong high far to the north will 
maintain a pocket of relatively strong trade winds in the gradient 
flow as the system dissipates from remnant low to a surface trough.


INIT  16/0300Z 17.7N 149.4W   40 KT  45 MPH
 12H  16/1200Z 17.6N 152.2W   35 KT  40 MPH
 24H  17/0000Z 17.4N 156.1W   30 KT  35 MPH...POST-TROP/REMNT LOW
 36H  17/1200Z 17.3N 160.0W   30 KT  35 MPH...POST-TROP/REMNT LOW
 48H  18/0000Z...DISSIPATED

Forecaster M Ballard/R Ballard

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