ZCZC HFOTCDCP1 ALL TTAA00 PHFO DDHHMM Hurricane Walaka Discussion Number 11 NWS Central Pacific Hurricane Center Honolulu HI CP012018 1100 PM HST Mon Oct 01 2018 Walaka continues to display a warm well defined eye surrounded by a ring of -65 to -85C cloud tops. The presentation in geostationary satellite imagery has changed very little since the previous advisory, with perhaps a bit of an improvement in organization over the past hour. The most recent morphed microwave imagery from UW- CIMSS indicates that Walaka may be going through an eyewall replacement cycle, so the down trend seen in the overall satellite presentation that began late Monday afternoon, may only be temporary. The latest intensity estimates from PHFO, SAB, JTWC all came in at 6.5 (127 knots) while ADT was 6.8 (135 knots). Given several satellite images Monday afternoon around 02/00Z showing T numbers of 7.0 (140 knots), and the likelihood that an eyewall replacement cycle is ongoing, the initial intensity was held at 140 knots for this advisory. The initial motion was set at 330/07 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. 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 remains closely aligned with the GFEX, TVCN, HCCA consensus guidance. The environment surrounding Walaka remains conducive for additional intensification during the next 24 to 36 hours. The tropical cyclone will remain within a deep moist airmass, with low vertical wind shear, and sea surface temperatures between 84 to 86 Fahrenheit. Eyewall replacement cycles will likely lead to fluctuation in intensity through this time frame, so the intensity forecast shows little intensity change through 36 hours. Beyond 36 hours, vertical wind shear will increase, drier mid-level air will begin to get wrapped into the cyclone, while sea surface temperatures become marginal and even unfavorable. As a result, Walaka should begin to weaken on Wednesday, with rapid weakening then expected through the end of the forecast period. The official forecast was not changed much from the previous advisory, and remains above all guidance through 36 hours and then trends closer to a blend of the statistical and dynamical models thereafter. The forecast track will take Walaka near Johnston Island on Tuesday, so the 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. Thus, a Hurricane Watch remains in effect for the region from Nihoa to Maro Reef. FORECAST POSITIONS AND MAX WINDS INIT 02/0900Z 13.7N 170.0W 140 KT 160 MPH 12H 02/1800Z 15.1N 170.3W 140 KT 160 MPH 24H 03/0600Z 17.3N 170.3W 140 KT 160 MPH 36H 03/1800Z 20.2N 169.4W 135 KT 155 MPH 48H 04/0600Z 23.5N 168.0W 115 KT 130 MPH 72H 05/0600Z 29.8N 167.3W 80 KT 90 MPH 96H 06/0600Z 32.5N 164.8W 65 KT 75 MPH 120H 07/0600Z 40.2N 157.7W 50 KT 60 MPH $$ Forecaster Jelsema NNNN