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Tropical Storm WALAKA

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.
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