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Hurricane Walaka Discussion Number  14...Corrected
NWS Central Pacific Hurricane Center Honolulu HI   CP012018
500 PM HST Tue Oct 02 2018
 
Walaka's eye has become less distinct in conventional satellite 
imagery over the last couple of hours, with subjective intensity 
estimates and CIMSS-ADT unanimous at 6.0. Thus, the current 
intensity has been lowered to 115 kt for this advisory. Despite 
these recent trends, a 0151 UTC SSMI pass continued to show a well-
developed eyewall, and there are well-developed outflow channels to 
the northeast and southeast of the hurricane. Outflow is much more 
restricted in the western semicircle. 

The initial motion estimate is 010/11, as Walaka moves generally 
toward a vertically-stacked low pressure area near 31N 170W. Walaka 
is expected to soon begin accelerating toward the north-northeast
as it gets caught up in the warm conveyor belt on the east side of
the low. As Walaka begins to get tangled up with this extratropical 
feature, the guidance shows the center will dramatically slow it's 
forward motion in the 48 to 72 hour time frame and may take a brief 
bend back toward the north-northwest, then kick northeast rapidly 
again at 96 hours and beyond as the circulation becomes more 
shallow. The track guidance remains in remarkably good agreement 
considering the rather complex interaction between Walaka and the 
extratropical low, and this forecast track is similar to the 
previous advisory package.

The UW-CIMSS shear analysis shows that Walaka will be coming under 
the influence of moderate to strong shear relatively soon. The shear
is expected to peak at greater than 30 kt by 36 hours, which should
continue the weakening trend. Although the shear diminishes beyond
36 hours, the cyclone will begin moving over increasingly cool sea
surface temperatures. There is some uncertainty as to how Walaka's
interaction with the extratropical low will play out. The global
models seem to be in good agreement that some semblance of a warm
core will remain even afterward, and so the forecast maintains
Walaka as a tropical cyclone through 96 hours. It would not be
surprising if the system becomes extratropical sooner, however. The
forecast shows a slower rate of weakening than most of the dynamical
models, in best agreement with the ECMWF through 48 hours, then
aligns with SHIPS guidance afterward.
 
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  03/0300Z 16.7N 170.2W  115 KT 130 MPH
 12H  03/1200Z 18.7N 169.7W  110 KT 125 MPH
 24H  04/0000Z 21.9N 168.5W  105 KT 120 MPH
 36H  04/1200Z 25.5N 167.4W   95 KT 110 MPH
 48H  05/0000Z 28.9N 167.6W   85 KT 100 MPH
 72H  06/0000Z 32.0N 166.4W   65 KT  75 MPH
 96H  07/0000Z 38.7N 160.6W   50 KT  60 MPH
120H  08/0000Z 46.8N 152.1W   40 KT  45 MPH...POST-TROP/EXTRATROP
 
$$
Forecaster R Ballard
 
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