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Tropical Storm Douglas Discussion Number 34
NWS Central Pacific Hurricane Center Honolulu HI EP082020
1100 AM HST Tue Jul 28 2020
There has been no deep convection associated with the low level
circulation center (LLCC) of Douglas for over 6 hours, leaving the
LLCC completely exposed and easy to track. Thanks to persistent 25
kt of southwesterly vertical wind shear, the closest deep
convection has been displaced over 100 nm to the northeast. Time as
a tropical cyclone is short for this system as it continues to track
west northwestward, spreading tropical storm force winds through
the Papahanaumokuakea Marine National Monument far northwest of the
main Hawaiian Islands.
Subjective Dvorak satellite intensity estimates range from 2.0/30
kt, from HFO and SAB, to 2.5/35 kt from JTWC. UW-CIMSS ADT is 39
kt. An ASCAT pass last evening reasonably justified a 45 kt strength
6 hours ago, but Douglas is likely weaker than that now. Douglas
was a category 1 hurricane slightly more than 24 hours ago, so some
constraint must be applied in the drive to weaken this system.
Given all these factors, initial intensity is set at 40 kt for this
forecast cycle.
Initial motion is 290/16 kt, part of a long term trend as Douglas
moves west northwestward along the southern flank of a low to mid-
level ridge. The forecast track is very close to the previous one,
tracing a shallow arc along GEMI and HCCA in the middle of the
tight guidance envelope. Vertical shear is forecast to decrease
while SST rises modestly along the forecast track but, without deep
convection, Douglas will not recover as a tropical system. However,
global models maintain a circulation center through 60 hours,
suggesting a prolonged life as a post-tropical remnant low before
total dissipation somewhere west of the dateline. For this forecast
cycle, Douglas is generously given another 24 hours as a weakening
tropical cyclone, followed by transition to a post tropical remnant
low at 36 hours just within the Central North Pacific.
FORECAST POSITIONS AND MAX WINDS
INIT 28/2100Z 24.5N 168.6W 40 KT 45 MPH
12H 29/0600Z 24.9N 171.4W 35 KT 40 MPH
24H 29/1800Z 25.4N 175.4W 35 KT 40 MPH
36H 30/0600Z 26.0N 179.4W 30 KT 35 MPH...POST-TROP/REMNT LOW
48H 30/1800Z 27.0N 176.7E 25 KT 30 MPH...POST-TROP/REMNT LOW
60H 31/0600Z 28.0N 172.8E 25 KT 30 MPH...POST-TROP/REMNT LOW
72H 31/1800Z...DISSIPATED
$$
Forecaster Powell
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