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Hurricane Walaka Discussion Number  21
NWS Central Pacific Hurricane Center Honolulu HI   CP012018
1100 AM HST Thu Oct 04 2018
 
The satellite presentation of Walaka has degraded significantly
under persistent southwesterly vertical wind shear. The low level
circulation center has become partially exposed, with deep
convection displaced to the northeast and east. Subjective Dvorak
current intensity estimates were 4.0/65 kt from SAB and 4.5/77 kt
out of HFO. CIMSS ADT yielded 82 kt, and a 1747Z CIMSS SATCON
estimate was at 77 kt. Given these inputs, the initial intensity
will be lowered to 80 kt, which could be generous.

Walaka is interacting with a deep, mid- to upper-level low to its
west, and the initial motion of the hurricane is toward the north at
19 kt. As this interaction continues into tonight, Walaka will lose
forward speed and make a turn toward the north-northwest. A broad
North Pacific trough moving in from the northwest will pick up
Walaka on Friday and cause it to accelerate toward the northeast. On
late Saturday and Sunday, the extratropical low of Walaka will race
toward the cold waters of the Gulf of Alaska. The forecast track was
changed little from previous advisory and is near the middle of a
tightly clustered guidance envelope near TVCE. 

Continued weakening is expected. Even though vertical wind shear
will decline later today, SSTs will drop below 26C, and continued
interaction with the deep low should maintain the weakening trend.
Vertical wind shear will steadily rise on Friday and Saturday, and
as Walaka accelerates over increasingly colder waters, transition to
an extratropical low could occur late Saturday or Sunday. For this
advisory, the rate of weakening was increased slightly to be in
better line with recent satellite trends, though still not as
aggressive as the statistical guidance. The intensity forecast is in
the middle of the guidance envelope near ICON and closest to HMON. 
 
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  04/2100Z 28.8N 166.3W   80 KT  90 MPH
 12H  05/0600Z 30.6N 167.0W   70 KT  80 MPH
 24H  05/1800Z 32.6N 166.6W   55 KT  65 MPH
 36H  06/0600Z 35.2N 164.5W   45 KT  50 MPH
 48H  06/1800Z 40.1N 160.5W   40 KT  45 MPH
 72H  07/1800Z 53.0N 149.0W   35 KT  40 MPH...POST-TROP/EXTRATROP
 96H  08/1800Z...DISSIPATED
 
$$
Forecaster Wroe
 
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