ZCZC HFOTCDCP1 ALL TTAA00 PHFO DDHHMM Tropical Storm Walaka Discussion Number 23 NWS Central Pacific Hurricane Center Honolulu HI CP012018 1100 PM HST Thu Oct 04 2018 The low level circulation center of Walaka has managed to find its way under a small area of deep convection this evening, likely a result of the decrease in vertical wind shear as indicated by the UW-CIMSS shear analysis, which showed 18 knots of shear from the northeast. Several microwave passes since 05/00Z have been helpful in locating the center position, and indicate that the forward speed of the cyclone has slowed considerably. The latest satellite intensity estimates were 3.5 (55 knots) from PHFO, 3.0 (45 knots) from SAB, while the ADT came in at 3.3 (51 knots). Meanwhile, an experimental Satcon estimate from UW-CIMSS showed an intensity of 59 knots. Given the large circulation of this storm and the satellite intensity estimates likely dropping the intensity too quickly, we will lean on the high end of the intensity estimates. As a result, the initial intensity for this advisory was lowered to 60 knots. The initial motion was set at 330/05 knots. Walaka continues to interact with a deep mid-upper level low in the vicinity of 27N 169W. This interaction should lead to a slower movement in a generally northward direction over tonight. A broad north Pacific upper trough moving in from the northwest, will then pick Walaka up and accelerate the cyclone off to the northeast Friday through Saturday, with Walaka expected to undergo the extra-tropical transition right around the 48 hour forecast point. The official forecast track was shifted to the right of the previous advisory to better align with the latest guidance. The forward motion was also decreased as guidance has slowed down the expected forward motion considerably, likely due to a later arrival of the broad north Pacific upper trough which will eventually lift and accelerate Walaka northeastward. Walaka will be over cool sea surface temperatures below 25C through the remainder of its journey across the Pacific, with vertical wind shear expected to increase substantially Friday night and Saturday. As a result, the official intensity forecast which was changed little from the previous advisory and remains in good agreement with the latest GFS and ECMWF models, calls for steady weakening. Walaka is expected to become an extra-tropical low by Saturday evening, with dissipation expected after forecast hour 72. FORECAST POSITIONS AND MAX WINDS INIT 05/0900Z 30.6N 168.3W 60 KT 70 MPH 12H 05/1800Z 31.7N 168.1W 55 KT 65 MPH 24H 06/0600Z 33.6N 166.4W 50 KT 60 MPH 36H 06/1800Z 37.3N 163.3W 45 KT 50 MPH 48H 07/0600Z 43.3N 158.6W 40 KT 45 MPH...POST-TROP/EXTRATROP 72H 08/0600Z 56.0N 144.0W 30 KT 35 MPH...POST-TROP/EXTRATROP 96H 09/0600Z...DISSIPATED $$ Forecaster Jelsema NNNN
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