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Hurricane Douglas Discussion Number  25
NWS Central Pacific Hurricane Center Honolulu HI   EP082020
500 AM HST Sun Jul 26 2020
 
Hurricane Hunters from the Air Force 53rd Weather Reconnaissance 
Squadron spent most of the night with Douglas, making 5 passes 
through the center. The final pass contained some of the strongest 
winds of the entire mission, with flight-level winds near 100 kt, 
SFMR winds up to 79 kt, and a relatively steady pressure reading 
near 983 mb. The initial intensity was maintained at 80 kt based on 
these valuable data points. Also of extreme value is the fact that 
the low-level center is south of the apparent center seen in 
conventional satellite imagery, and closer to the islands than 
might be otherwise expected. Although island-based radars are also 
detecting Douglas' circulation, they are sampling the upper 
portions of the cyclone that are sheared northward due to southerly 
vertical wind shear. 

Despite the vertical wind shear, Douglas has been slow to weaken, 
and this trend will continue today as Douglas passes near, or 
potentially over, the islands. Steadily increasing SSTs along the 
forecast track are expected to limit the rate of weakening, while 
the noted vertical wind shear may be confined to the upper-levels. 
While Douglas is on the western edge of a ridge aloft, leading to 
high-level southerly shear, a mid-level ridge is expected to build 
westward to the north of Douglas through Monday, likely allowing 
the low- to mid-level core of the cyclone to remain intact. The 
updated intensity forecast once again closely follows the consensus 
IVCN, and maintains Douglas as a hurricane until it passes west of 
the islands. Steady weakening will occur thereafter due to 
persistent southwesterly shear. 

The mid-level ridge will continue to drive Douglas toward the west-
northwest, with the current motion vector estimated to be 285/14 
kt. The forecast track takes the center of Douglas dangerously close 
to the islands from Maui to Kauai through tonight, where a Hurricane 
Warning is in effect. The updated forecast track is very close to 
the previous forecast and the high-performing ECMWF guidance, and 
anticipates some acceleration toward the west in the later periods 
as the increasingly shallow system gets steered by the low-level 
trade wind flow. 

Key Messages

1. Douglas will pass dangerously close to, or over, the islands 
today, bringing a triple threat of hazards, including but not 
limited to damaging winds, flooding rainfall, and dangerously high 
surf, especially along east and north facing shores.

2. It is remains important that you do not focus on the exact 
forecast track of Douglas. Due to Douglas' angle of approach to the 
islands, any wobble 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. 
Hurricane force wind gusts are possible even within the tropical 
storm warning area. Winds will also be stronger at the upper floors 
of high rise buildings.

 
FORECAST POSITIONS AND MAX WINDS
 
INIT  26/1500Z 20.7N 154.3W   80 KT  90 MPH
 12H  27/0000Z 21.4N 156.6W   75 KT  85 MPH...NEAR MAUI COUNTY
 24H  27/1200Z 22.3N 159.5W   70 KT  80 MPH...NEAR KAUAI
 36H  28/0000Z 22.8N 162.7W   60 KT  70 MPH
 48H  28/1200Z 23.3N 166.1W   55 KT  65 MPH
 60H  29/0000Z 23.7N 169.5W   50 KT  60 MPH
 72H  29/1200Z 24.0N 173.0W   45 KT  50 MPH
 96H  30/1200Z 24.5N 179.5E   35 KT  40 MPH
120H  31/1200Z 25.5N 172.0E   30 KT  35 MPH
 
$$
Forecaster Birchard
 
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