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Hurricane Walaka Discussion Number  22
NWS Central Pacific Hurricane Center Honolulu HI   CP012018
500 PM HST Thu Oct 04 2018
 
The satellite presentation of Walaka continues to degrade rapidly as
the cyclone interacts with a mid- to upper-level low. A diminishing
amount of deep convection remains confined to the northeast of the
exposed low-level circulation center, and outflow is restricted in
the northwest and south quadrants. Subjective Dvorak current
intensity estimates are down to 3.5/55 kt from SAB and 4.0/65 kt
out of HFO, while CIMSS ADT yields 59 kt. Given these inputs and
the poor satellite presentation, the initial intensity will be
lowered to 65 kt.

The initial motion is toward the northwest (325 degrees) at 16 kt,
as Walaka rotates around the northern edge of the mid- to 
upper-level low. As this interaction continues through tonight,
Walaka will lose forward speed and make a turn toward the north. A
broad North Pacific trough moving in from the northwest will pick up
Walaka on Friday and cause the cyclone to accelerate toward the
northeast. On Saturday and Sunday, the extratropical low of Walaka
will race toward the cold waters of the Gulf of Alaska. The forecast
track was shifted to the left of the prior advisory to account for
recent motion and remains near TVCE in the middle of a rather
tightly clustered guidance envelope. 

Continued weakening is expected. Vertical wind shear is declining
and will be light tonight and Friday. However, SSTs will drop below
25C, and this, along with continued interaction with the deep low,
should maintain the weakening trend. Late Friday and Saturday, the
approaching, broad North Pacific trough will produce increasing
vertical wind shear and cause the cyclone to accelerate
northeastward over increasingly colder waters. Under these hostile
conditions, transition to an extratropical low is forecast to occur
by Saturday, though it may happen much earlier if convection fails
to redevelop. Given recent satellite trends, the rate of short term
weakening was increased from the previous advisory. The remainder of
the forecast was changed little and remains in the middle of the
guidance envelope near ICON.
 
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  05/0300Z 30.2N 168.0W   65 KT  75 MPH
 12H  05/1200Z 32.0N 168.2W   55 KT  65 MPH
 24H  06/0000Z 34.4N 166.6W   50 KT  60 MPH
 36H  06/1200Z 38.6N 163.0W   45 KT  50 MPH
 48H  07/0000Z 44.7N 158.0W   35 KT  40 MPH...POST-TROP/EXTRATROP
 72H  08/0000Z 56.8N 146.3W   30 KT  35 MPH...POST-TROP/EXTRATROP
 96H  09/0000Z...DISSIPATED
 
$$
Forecaster Wroe
 
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