ZCZC HFOTCDCP1 ALL TTAA00 PHFO DDHHMM Tropical Storm Walaka Discussion Number 3 NWS Central Pacific Hurricane Center Honolulu HI CP012018 1100 PM HST Sat Sep 29 2018 The satellite presentation of Walaka has improved this evening, with an increase in deep convection around the low level circulation center. Several microwave passes were helpful in determining the center location, but also indicated that the tropical storm lacks good organization at the moment. The latest satellite intensity estimates from PHFO, SAB and JTWC all came in at 2.5 (35 knots) with the ADT value from UW-CIMSS appearing unrealistically high at 3.6 (57 knots). As a result, the initial intensity for this advisory will be held at 35 knots. The initial motion based on interpolating between microwave passes along with geostationary satellite animations will be set at 270/14 knots. Walaka is expected to track nearly due west along the south side of a subtropical ridge through Sunday night, with a gradual decrease in forward speed. A deep north Pacific upper trough will erode the subtropical ridge to the north of Walaka on Monday and steer the tropical cyclone northwestward, with a turn toward the north and northeast along with an increase in forward speed forecast beyond 72 hours. The guidance is fairly tightly clustered through 48 hours with increasing model spread from forecast hour 72 onward. The official forecast closely follows the GFEX and TVCN consensus models through 48 hours, and lies nearly on top of the track from the previous advisory. Beyond 48 hours, the official forecast track was nudged to the right to better align with the latest consensus guidance. Of note, the forecast track currently brings the center of Walaka very near Johnston Atoll, late Monday night or early Tuesday, and watches will likely be needed on Sunday. The environmental conditions surrounding Walaka will remain very conducive for intensification over the next several days, with high sea surface temperatures of 84 to 86 Fahrenheit, 10 knots or less of vertical wind shear, high ocean heat content, and plenty of deep moisture. As a result, the forecast calls for steady intensification over the next 24 hours as the system becomes better organized, with rapid intensification expected between forecast hour 24 and forecast hour 48, with Walaka expected to become a major hurricane by Monday night. Wind shear should begin to impact the system as it interacts with a deep upper level trough beyond 72 hours, and the forecast calls for steady weakening by forecast hours 96 and 120. The official intensity forecast is generally a blend between the statistical and dynamical models, with the dynamical models showing even a faster rate of intensification than the official forecast. FORECAST POSITIONS AND MAX WINDS INIT 30/0900Z 11.6N 162.1W 35 KT 40 MPH 12H 30/1800Z 11.8N 164.2W 50 KT 60 MPH 24H 01/0600Z 12.1N 166.6W 65 KT 75 MPH 36H 01/1800Z 12.8N 168.3W 90 KT 105 MPH 48H 02/0600Z 14.0N 169.4W 110 KT 125 MPH 72H 03/0600Z 17.9N 169.7W 110 KT 125 MPH 96H 04/0600Z 24.5N 167.5W 95 KT 110 MPH 120H 05/0600Z 30.5N 167.5W 75 KT 85 MPH $$ Forecaster Jelsema NNNN