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Hurricane DOUGLAS

Hurricane Douglas Discussion Number  27
NWS Central Pacific Hurricane Center Honolulu HI   EP082020
500 PM HST Sun Jul 26 2020
In spite of increasing southerly vertical wind shear of more than 
20 kt, a large burst of convection redeveloped around a ragged eye 
late this afternoon. Hurricane Hunters from the Air Force 53rd 
Weather Reconnaissance Squadron have departed Douglas after spending 
much of the day sampling the system, and another mission is 
scheduled for this evening. While the last passes through continued 
to show a slow increase in central pressure, aircraft data indicated 
that the winds had not changed much, and recent land-based radar 
showed winds in excess of 90 kt at around 6,000 ft. As a result, the 
initial intensity will be held at 75 kt for this advisory, which is 
in line with the PHFO Dvorak CI of 4.5. 

Of greater importance, the aircraft data and land-based radars 
indicated that Douglas has taken a jog to the north today. While 
the low-level ridge to the north is providing significant steering, 
a weakness in the ridge aloft and increasing vertical wind shear, 
mainly at higher levels, have likely caused the hurricane to make a 
northward shift, resulting in an initial motion of 295/14 kt. 
Douglas will continue on this general motion tonight as it passes 
near Oahu and Kauai, eventually making a turn and an acceleration 
toward the west late Monday through Thursday. Due to the northward 
jog, the track forecast was nudged slightly to the north through 
Monday and is close to the middle of a tightly clustered guidance 
envelope through Thursday.

Slow weakening will continue, though Douglas will remain a 
hurricane as it passes near Oahu and Kauai tonight. SSTs will slowly 
increase along the forecast track, but southerly vertical wind shear 
will tilt the system and disrupt the circulation aloft, leading to 
gradual weakening through at least the next four days. The 
intensity forecast was changed little from the prior advisory and is 
near IVCN in the middle of the guidance envelope, though lower than 
the statistical guidance.

The motion of Douglas has allowed the Hurricane Warning for Maui 
County to be canceled. Given the close approach to both Oahu and 
Kauai along with the ongoing development of deep convection, the 
Hurricane Warning remains in place for Oahu and Kauai.

Key Messages

1. Douglas will pass dangerously close to Oahu and Kauai tonight, 
producing 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 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 drastic differences in where 
the worst weather occurs. Even if the center remains offshore, 
severe impacts could extend well from the center and be realized 
over Oahu and Kauai.
3. Terrain effects can cause strong localized acceleration of the 
wind through gaps and where winds blow downslope. These 
areas will shift with time as Douglas passes near Oahu and Kauai.
INIT  27/0300Z 22.0N 157.3W   75 KT  85 MPH
 12H  27/1200Z 22.5N 159.6W   70 KT  80 MPH...NEAR KAUAI
 24H  28/0000Z 23.1N 162.7W   60 KT  70 MPH
 36H  28/1200Z 23.5N 166.3W   55 KT  65 MPH
 48H  29/0000Z 23.9N 170.0W   50 KT  60 MPH
 60H  29/1200Z 24.1N 173.8W   45 KT  50 MPH
 72H  30/0000Z 24.2N 177.7W   40 KT  45 MPH
 96H  31/0000Z 25.0N 174.6E   35 KT  40 MPH
120H  01/0000Z 27.2N 167.7E   35 KT  40 MPH
Forecaster Wroe