000 WTPA42 PHFO 270255 TCDCP2 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 acceleration areas will shift with time as Douglas passes near Oahu and Kauai. FORECAST POSITIONS AND MAX WINDS 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