ZCZC HFOTCDCP1 ALL TTAA00 PHFO DDHHMM Tropical Storm Walaka Discussion Number 2 NWS Central Pacific Hurricane Center Honolulu HI CP012018 500 PM HST Sat Sep 29 2018 The satellite presentation of Walaka has not changed significantly since this morning. The banding feature to the east and south of the center has become less distinct, though a large area of deep convection has persisted near the center. Subjective Dvorak current intensity estimates range from 2.0/30 kt out of JTWC to 2.5/35 kt from HFO and SAB. The initial intensity will be held at 35 kt for this advisory. Walaka continues to move toward the west (265 degrees) at 13 kt. A deep ridge to the north will steer Walaka on a general westward motion through Sunday, taking the cyclone well southwest of the main Hawaiian Islands. Late Sunday through Monday night, Walaka will make a gradual turn toward the northwest then north as a deep North Pacific trough digs southward and steadily erodes the ridge. As a result, Walaka will pass very close to, or over, Johnston Atoll as early as Monday night and likely on Tuesday. The deep trough will stall roughly along 171W longitude on Tuesday, and as interaction with the trough increases, Walaka will accelerate northward on days four and five. This should take the system across the Papahanaumokuakea Marine National Monument. The track guidance envelope is tightly clustered through 72 hours, with differences in forward motion increasing thereafter. Through 72 hours, the track forecast is essentially unchanged and lies near the middle of the tightly clustered guidance envelope. On days four and five, the forecast forward motion has been accelerated to follow the TVCE and HMON, which are slower than the GFS and faster than the ECMWF. Strengthening, possibly rapid, is expected through the next three days. Walaka will remain under low vertical wind shear and over SSTs of around 29C through at least Monday and likely into early Tuesday. In this environment, the bulk of the intensity guidance shows rapid intensification during the next 48 hours, and the SHIPS rapid intensification guidance for Walaka remains well above the climatological mean through 72 hours. On days four and five, interaction with the deep trough will create increasing vertical wind shear that should lead to weakening. The intensity forecast was changed little from the prior advisory and is close to LGEM between SHIPS and HMON, near the middle of the guidance envelope. Walaka is forecast to become a hurricane by Sunday, and along the forecast track, hurricane conditions could be experienced on Johnston Atoll as early as Monday night. FORECAST POSITIONS AND MAX WINDS INIT 30/0300Z 11.4N 160.5W 35 KT 40 MPH 12H 30/1200Z 11.6N 162.7W 50 KT 60 MPH 24H 01/0000Z 11.9N 165.4W 65 KT 75 MPH 36H 01/1200Z 12.4N 167.5W 80 KT 90 MPH 48H 02/0000Z 13.5N 168.8W 95 KT 110 MPH 72H 03/0000Z 16.9N 169.6W 110 KT 125 MPH 96H 04/0000Z 22.9N 168.3W 95 KT 110 MPH 120H 05/0000Z 30.1N 168.5W 70 KT 80 MPH $$ Forecaster Wroe NNNN