ZCZC HFOTCDCP1 ALL TTAA00 PHFO DDHHMM Hurricane Walaka Discussion Number 12 NWS Central Pacific Hurricane Center Honolulu HI CP012018 500 AM HST Tue Oct 02 2018 The satellite presentation of Walaka which was being degraded by an eye wall replacement cycle overnight, has just begun to improve with a ring of deep convection beginning to once again encircle the well defined eye, which could be a sign that the eyewall replacement cycle is getting ready to complete. The latest intensity estimates from PHFO, SAB, JTWC were 6.5 (127 knots) while the ADT held at 6.6 (130 knots). Based on constraints likely holding the intensity of Walaka too low Monday afternoon, have only reduced the initial intensity slightly with this advisory to 135 knots. The initial motion was set at 350/09 knots. A deep north Pacific upper level low in the vicinity of 30N 170W will draw Walaka northward over the next several days, before another sharp upper trough shifting across the north Pacific picks the tropical cyclone up and shifts it off to the northeast Friday night and Saturday. Overall the guidance envelope remains fairly tightly clustered through the forecast period. The official forecast remains very close to that of the previous advisory and is fairly well aligned with the latest GFEX, TVCN, HCCA consensus guidance. The environment surrounding Walaka remains conducive for additional intensification during the next 24 hours. The tropical cyclone will remain within a deep moist airmass with low vertical wind shear, high ocean heat content and sea surface temperatures between 84 to 86 Fahrenheit. Eyewall replacement cycles could lead to some fluctuations in intensity through this time frame, so the intensity forecast shows little intensity change through 24 hours. Beyond 24 hours, the combination of increasing vertical wind shear, drier mid-level air entraining into the cyclone, sea surface temperatures becoming marginal and even unfavorable, along with interaction with the deep upper level low should result in steady and even rapid weakening of Walaka. As a result, the intensity forecast calls for Walaka to begin weakening on Wednesday, with rapid weakening then continuing through the end of the forecast period. The official intensity forecast was adjusted downward slightly, but remains above all guidance through 36 hours before trending closer to a blend of the statistical and dynamical models thereafter. Walaka is expected to become an post-tropical/extra-tropical low by 120 hours. The forecast track will take Walaka near Johnston Island later today, with hurricane conditions expected this afternoon and this evening. Therefore a Hurricane Warning remains in effect for this location. The forecast track also takes the hurricane across the Papahanaumokuakea Marine National Monument between French Frigate Shoals and Laysan Island late Wednesday. Therefore, a Hurricane Watch remains in effect for the region from Nihoa to Maro Reef. FORECAST POSITIONS AND MAX WINDS INIT 02/1500Z 14.7N 170.0W 135 KT 155 MPH 12H 03/0000Z 16.2N 170.2W 135 KT 155 MPH 24H 03/1200Z 18.9N 169.7W 135 KT 155 MPH 36H 04/0000Z 22.3N 168.4W 120 KT 140 MPH 48H 04/1200Z 26.2N 167.4W 100 KT 115 MPH 72H 05/1200Z 30.5N 168.0W 75 KT 85 MPH 96H 06/1200Z 33.0N 164.0W 60 KT 70 MPH 120H 07/1200Z 41.0N 157.5W 50 KT 60 MPH...POST-TROP/EXTRATROP $$ Forecaster Jelsema NNNN