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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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