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Tropical Storm Walaka Discussion Number  26
NWS Central Pacific Hurricane Center Honolulu HI   CP012018
500 PM HST Fri Oct 05 2018
 
Walaka's satellite presentation has changed little since this 
morning, with an exposed low level circulation center (LLCC) 
embedded within low cloud swirls and occasionally open to the west. 
Cooler-topped layered clouds, along with a single sputtering 
cumulonimbus, mark the southeast flank. A 2120Z ASCAT pass showed 
two small patches of 45 kt winds beneath the layered clouds, while 
the entire western semicircle had winds of 30 kt or less. Latest 
Dvorak current intensity estimates range from 1.5/25 kt from JTWC
to 2.5/35 kt from PHFO. SAB considered this system too weak to
classify while ADT from UW-CIMSS was 43 kt. Using a mix of these
estimates and an assumption of continued weakening from this
morning's ASCAT pass, we will assign an initial intensity of 40 kt
for this advisory. 

This weakening system is tracking northeastward, with initial motion
of 040/12 kt. After moving northward over the past few days along
the western fringe of the subtropical ridge, Walaka has begun to
respond to southwesterly steering ahead of a broad north Pacific 
upper trough moving in from the northwest. This will pick Walaka up 
and accelerate it off to the northeast through Sunday. Walaka is 
expected to begin extra-tropical transition Saturday. The official 
forecast track lies along the right side of the very tight guidance 
envelope, following an arc just to the left of CTCI. This track, 
adjusted slightly to the right to account for initial motion, 
terminates at 48 hours as Walaka becomes absorbed by a mid-latitude 
low.

Walaka will move over increasingly cooler water along its truncated 
track, while vertical wind shear dramatically ramps up, reaching 36 
kt at 36 hours and 52 kt by 48 hours. Global models show Walaka
will be absorbed by a mid-latitude low by 48 hours, with weakening
and extratropical transition occurring simultaneously from 24 hours 
through system dissipation at 48 hours. Our forecast follows the
previous curve, closely tracing ICON.
 
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  06/0300Z 32.9N 166.6W   40 KT  45 MPH
 12H  06/1200Z 35.4N 164.1W   35 KT  40 MPH
 24H  07/0000Z 40.9N 159.0W   30 KT  35 MPH...POST-TROP/EXTRATROP
 36H  07/1200Z 46.9N 154.4W   25 KT  30 MPH...POST-TROP/EXTRATROP
 48H  08/0000Z...DISSIPATED
 
$$
Forecaster Powell
 
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