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Tropical Storm Walaka Discussion Number  25
NWS Central Pacific Hurricane Center Honolulu HI   CP012018
1100 AM HST Fri Oct 05 2018
 
Walaka, which has been deteriorating steadily all night, is now 
coming apart at the seams in satellite imagery. The exposed low 
level circulation center (LLCC) is beginning to open up to the
west, with layered clouds and possibly a single warm-topped
cumulonimbus sputtering within the eastern quadrant. The latest
Dvorak current intensity estimates range from 1.5/25 kt from JTWC to
3.0/45 kt from PHFO. SAB estimated 2.0/30 kt while UW-CIMSS ADT was
39 kt. Based on these estimates, and with a nod to continuity, we
will assign an initial intensity of 45 kt for this advisory.
However, this may be generous given the poor satellite presentation
and the Dvorak constraints keeping the PHFO estimate high.

This weakening system is tracking just east of due north, with 
initial motion of 030/10 kt. After moving northward over the past 
few days along the western fringe of the subtropical ridge, Walaka 
is beginning 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 early 
Sunday. Walaka is expected to begin extra-tropical transition 
Saturday. The official forecast track is very close to that of the 
previous advisory, staying within the very tight guidance envelope 
centered along HWRF. The track 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 34 
kt at 36 hours and 44 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 
HCCA weakening trend, which is also quite close to the IVCN curve.
 
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  05/2100Z 32.2N 167.8W   45 KT  50 MPH
 12H  06/0600Z 34.7N 166.2W   40 KT  45 MPH
 24H  06/1800Z 39.4N 162.6W   35 KT  40 MPH...POST-TROP/EXTRATROP
 36H  07/0600Z 45.7N 157.2W   30 KT  35 MPH...POST-TROP/EXTRATROP
 48H  07/1800Z...DISSIPATED
 
$$
Forecaster Powell
 
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