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Hurricane DOUGLAS

Hurricane Douglas Discussion Number  24
NWS Central Pacific Hurricane Center Honolulu HI   EP082020
1100 PM HST Sat Jul 25 2020
Hurricane Hunters from the Air Force 53rd Weather Reconnaissance 
Squadron have been flying through and around the center of Douglas 
through the evening, providing valuable ground truth. Latest data 
support maintaining Douglas' initial intensity at 80 kt, with 
maximum flight-level winds near 90 kt, SFMR winds as high as 78 kt, 
and a central pressure near 983 mb. Worth noting that the data also 
indicate that the low-level center is south of the center that is 
seen in conventional satellite imagery. Recent microwave images 
confirm that the cyclone is tilted to the north with height, due to 
southerly vertical wind shear. 

Despite the vertical wind shear, Douglas is expected to only slowly 
weaken as it comes dangerously close to the Hawaiian Islands. This 
is primarily due to steadily increasing SSTs along the forecast 
track, and also likely due to the fact that most of the shear is in 
the upper levels. While Douglas has rounded the southwestern 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, likely allowing the low- to mid-level core of the cyclone 
to remain intact. The updated intensity forecast closely follows 
the consensus IVCN, and maintains Douglas as a hurricane as it 
passes near Oahu and Kauai County. 

The mid-level ridge will continue to drive Douglas toward the west-
northwest, with the current motion vector estimated to be 290/14 
kt. The forecast track takes the center of Douglas dangerously close 
to Oahu and Kauai on Sunday, with some of the guidance indicating a 
slight jog toward the west Sunday evening near Oahu, necessitating 
a Hurricane Warning for Kauai County. Douglas will potentially 
impact parts of the Papahanaumokuakea Marine National Monument on 
Monday and Tuesday. The updated forecast track is very close to the 
previous forecast, the track consensus TVCN, and is on the southern 
side of most of the guidance. However the GFS and ECMWF ensemble 
means are just left of the official forecast, suggesting a 
potentially more impactful scenario for Kauai County and Oahu. 

Key Messages

1. Douglas continues to approach the main Hawaiian Islands, and 
will pass dangerously close to, or over, the islands Sunday. 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. 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. 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.
INIT  26/0900Z 20.4N 152.8W   80 KT  90 MPH
 12H  26/1800Z 21.1N 155.0W   75 KT  85 MPH
 24H  27/0600Z 21.8N 157.9W   70 KT  80 MPH
 36H  27/1800Z 22.5N 160.6W   65 KT  75 MPH
 48H  28/0600Z 23.2N 163.6W   55 KT  65 MPH
 60H  28/1800Z 23.6N 166.8W   50 KT  60 MPH
 72H  29/0600Z 24.0N 170.0W   45 KT  50 MPH
 96H  30/0600Z 24.0N 177.3W   35 KT  40 MPH
120H  31/0600Z 25.0N 175.0E   30 KT  35 MPH
Forecaster Birchard