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Hurricane Douglas Discussion Number  21
NWS Central Pacific Hurricane Center Honolulu HI   EP082020
500 AM HST Sat Jul 25 2020
 
The satellite presentation of Douglas has changed very little since 
the previous advisory, with the eye remaining cloud filled 
and difficult to locate with a high degree of certainty. The 
latest current intensity estimates from the satellite agencies came 
in at 5.0 (90 knots) from PHFO, 4.5 (77 knots) from JTWC and SAB, 
while the ADT from UW-CIMSS was 4.6 (80 knots). Based on the 
U.S. Air Force 53rd Weather Reconnaissance Squadron mission 
last evening finding maximum flight level winds of 108 knots (97 
knots with appropriate wind reduction factor to the surface from the 
700 mb flight level) and SFMR winds of 93 knots, we will 
conservatively lower the initial intensity to 90 knots with this 
advisory, but that may be generous. Douglas appears to have made a 
subtle shift toward the west overnight, and the initial motion 
for this advisory has been set at 290/16 knots.
 
The tropical cyclone will be going over the coolest sea 
surface temperatures (SSTs) along its forecast track during the 
next 12 to 18 hours before SSTs climb back to 26C or above. This 
should result in continued weakening despite relatively low 
vertical wind shear. Thereafter, the vertical wind shear slowly 
becomes less conducive for intensification, while SSTs become less 
hostile as they rise back to 26/27C or above. We expect that the 
increasing wind shear will win the battle through the remainder of 
the forecast track, and show slow and gradual weakening through 120 
hours. The official intensity forecast has changed very little from 
the previous advisory, and generally follows a blend of the 
corrected consensus and statistical model guidance.
 
Douglas is forecast to continue to move off to the west-northwest 
today toward a weakness in the sub-tropical ridge north of the 
Hawaiian Islands, with a slight reduction in forward speed. The 
subtropical ridge is forecast to strengthen north of the state 
tonight through the remainder of the weekend and this should steer 
the tropical cyclone slightly more westward, and over or very near
the Hawaiian Islands late tonight through Sunday night. Douglas is 
then expected to exit to the west of the island chain early 
next week. The official track forecast is virtually identical to the
previous advisory, and continues to hug the southern end of the
guidance envelope. This track is roughly in the middle of the 
deterministic GFS/ECMWF solutions and the GFS/ECMWF ensemble 
means, which is very close to the corrected consensus guidance HCCA.
 
Based on the latest intensity and track forecast, a Tropical Storm 
Watch has been issued for Kauai County. Tropical Storm
Warnings remain in effect for Hawaii County and Maui County. A
Hurricane Watch remains in effect for Hawaii County, Maui County and
Oahu. Finally, a Tropical Storm Warning will likely be required 
for Oahu later today. 
 
Key Messages
 
1. Douglas continues to approach the main Hawaiian Islands,
potentially passing dangerously close to, or over, the islands
late tonight through Sunday night. The close passage of Douglas
brings a triple threat of hazards, including but not limited to
damaging winds, flooding rainfall, and dangerously high surf,
especially along east facing shores.
 
2. It is vital that you do not focus on the exact forecast track or
intensity of Douglas, and remain prepared for changes to the
forecast. Due to Douglas' angle of approach to the islands, any
small changes in the track could lead to significant differences in
where the worst weather occurs. Even if the center remains
offshore, severe impacts could still be realized over the islands,
as they extend well away from the center.
 
3. Terrain effects can cause strong localized acceleration of
the wind through gaps and where winds blow downslope. These
acceleration areas will shift with time as Douglas passes near the
islands. Winds will also be stronger at the upper floors of
high rise buildings.
 
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  25/1500Z 19.1N 148.4W   90 KT 105 MPH
 12H  26/0000Z 19.7N 150.6W   75 KT  85 MPH
 24H  26/1200Z 20.6N 153.5W   70 KT  80 MPH
 36H  27/0000Z 21.4N 156.3W   65 KT  75 MPH
 48H  27/1200Z 22.1N 159.4W   60 KT  70 MPH
 60H  28/0000Z 22.7N 162.6W   55 KT  65 MPH
 72H  28/1200Z 23.2N 166.0W   50 KT  60 MPH
 96H  29/1200Z 24.1N 172.8W   45 KT  50 MPH
120H  30/1200Z 25.3N 179.2W   35 KT  40 MPH
 
$$
Forecaster Jelsema
 
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