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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.
FORECAST POSITIONS AND MAX WINDS
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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