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Hurricane Walaka Discussion Number  17
NWS Central Pacific Hurricane Center Honolulu HI   CP012018
1100 AM HST Wed Oct 03 2018

Satellite imagery shows Walaka apparently feeling the effects of
increasing vertical wind shear.  The deep convection on
the west and southwestern eyewall has narrowed, and the upper level
cirrus outflow is being eroded to the southwest and elongating off
to the northeast. The current intensity is held at 120 kt for this
advisory based on a blend of the latest subjective Dvorak estimates
and the ADT from UW-CIMSS. These range from 5.5/102 kt from SAB to
7.0/140 kt from JTWC to 6.6/130 kt from the ADT.
 
Walaka has continued accelerating toward the north-northeast
this morning, and the initial motion for this advisory is 020/19
kt. Walaka is expected to continue accelerating a bit more toward
the north-northeast into tonight as it remains under the influence
of steering flow around a deep low pressure system to the north. 
Once the hurricane gets closer to this extratropical low pressure
feature, it is expected to slow considerably. There is good
agreement in this scenario, with only minor northward changes in the
track through Friday, due to faster motion in the short term.  
Beyond Friday, Walaka gets picked up by a trough moving along in
the westerlies and accelerates off to the northeast, becoming
extratropical by Sunday.
 
Rapid weakening is forecast tonight and Thursday as continued
vertical wind shear values of up to 35 kt combine with SST dropping
below 27 degrees C.  Later on Thursday, the vertical wind shear
relaxes, but continued weakening is expected due to cooler SSTs.  As
Walaka gets picked up in the westerlies, a slow weakening is
forecast as it transitions to extratropical status. The intensity
forecast is near the stronger statistical guidance, SHIPS, and
higher resolution dynamical guidance, HWRF/HMON, and represents a
compromise between the stronger GFS/ECMWF and much weaker HCCA and
LGEM.
 
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  03/2100Z 21.4N 168.5W  120 KT 140 MPH
 12H  04/0600Z 24.2N 167.4W  110 KT 125 MPH
 24H  04/1800Z 27.9N 167.0W   85 KT 100 MPH
 36H  05/0600Z 30.5N 167.3W   70 KT  80 MPH
 48H  05/1800Z 32.4N 166.7W   55 KT  65 MPH
 72H  06/1800Z 40.0N 160.6W   45 KT  50 MPH
 96H  07/1800Z 51.5N 149.0W   35 KT  40 MPH...POST-TROP/EXTRATROP
120H  08/1800Z...DISSIPATED
 
$$
Forecaster Brenchley
 
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