ZCZC HFOTCDCP1 ALL TTAA00 PHFO DDHHMM Hurricane Walaka Discussion Number 6 NWS Central Pacific Hurricane Center Honolulu HI CP012018 500 PM HST Sun Sep 30 2018 Walaka's well defined deep convective wrapping pattern has morphed into a cloudy eye pattern in visible imagery this afternoon. Satellite loop shows system outflow is good across all quadrants and overall system symmetry and organization continue to improve. Subjective Dvorak current intensity (CI) estimates range from 4.0/65 kt from JTWC and PHFO to 4.5/77 kt from SAB. ADT from UW-CIMSS is 68 kt. Given the presence of a cloudy eye and higher overall CI estimates from the analysis centers, we will set the initial intensity at 65 kt for this advisory. Walaka is now a hurricane. The overall forecast philosophy for Walaka is unchanged. This system continues moving slightly north of due west along the southern flank of the subtropical ridge. Global models show a deep upper trough will dig southward, eroding the western edge of the subtropical ridge to the north of Walaka on Monday. This will steer Walaka northwestward, then northward on Tuesday. Track guidance remains very tightly clustered through Friday, greatly increasing confidence in the timing of the curve northward. Our forecast closely follows the previous one, with another tap to the west from 12 to 36 hours needed to stay within the very tight guidance envelope. A small tap to the east at 72 hours was needed for the same reason. With the official forecast track bringing the center of Walaka very near Johnston Atoll on Tuesday, a Hurricane Warning is now in effect there. Walaka remains within ideal conditions for strengthening, with high SSTs, low shear, high ocean heat content and plenty of deep moisture. SHIPS shows vertical shear will remain below 20 kt through 48 hours, ramping up to near 30 kt by day 3 and beyond. SSTs stay above 28 degrees C until day 3 even as Walaka tracks northward. Our forecast calls for rapid intensification through day 2, with Walaka reaching major hurricane status on Monday. After leveling off between days 2 and 3, increasing vertical shear and decreasing SSTs should begin to take their toll on this system. Steady weakening is forecast for day 3 and beyond. Our intensity forecast trends are close to those in the previous advisory, following HWRF. Some of the intensity guidance, like SHIPS, strengthens Walaka into the 130 to 140 kt range by day 2, with the probability for rapid intensification exceeding 90%. While we cap this system at 120 kt for this advisory, subsequent advisory packages may begin to reflect a stronger maximum intensity. FORECAST POSITIONS AND MAX WINDS INIT 01/0300Z 11.9N 166.4W 65 KT 75 MPH 12H 01/1200Z 12.3N 167.9W 85 KT 100 MPH 24H 02/0000Z 13.3N 169.4W 105 KT 120 MPH 36H 02/1200Z 14.8N 170.3W 115 KT 130 MPH 48H 03/0000Z 17.2N 170.3W 120 KT 140 MPH 72H 04/0000Z 22.7N 168.8W 110 KT 125 MPH 96H 05/0000Z 28.3N 168.3W 80 KT 90 MPH 120H 06/0000Z 32.1N 167.3W 60 KT 70 MPH $$ Forecaster Powell NNNN
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