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Hurricane Walaka Discussion Number  15...Corrected
NWS Central Pacific Hurricane Center Honolulu HI   CP012018
1100 PM HST Tue Oct 02 2018
 
Walaka's eye remains somewhat ragged in infrared satellite imagery
early this evening. However, a 0528Z SSMS pass continued to show a
well defined eye surrounded by a complete eyewall. The degradation
of the system in conventional satellite imagery is likely the
result of increasing vertical wind shear from the southwest. The
latest subjective Dvorak current intensity estimates from JTWC and
PHFO were 6.0/115 kt and 5.5/102 kt from SAB. The UW-CIMSS ADT
estimate was also 6.0/115 kt. Based on these estimates, we will
maintain Walaka's initial intensity at 115 kt for this advisory.
 
The initial motion for this advisory is 005/11 kt. Walaka is being
steered towards 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 outer circulation along
the southeastern and eastern periphery of this deep low. Once Walaka
gets closer to this extratropical feature, the track guidance
indicates its forward motion will slow in the 36 to 48 hour time.
It may make a brief bend back toward the north-northwest, then track
rapidly northeastward between 72 and 96 hours 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. This latest track forecast is very close
to the previous advisory package.
 
As the vertical wind shear near Walaka becomes increasingly hostile
during the next 24 to 36 hours, steady weakening is forecast.
Although the shear diminishes somewhat beyond 36 hours, the tropical
cyclone will begin moving over increasingly cool sea surface
temperatures and reduced ocean heat content. There is some
uncertainty about how Walaka's interaction with the extratropical
low will affect its intensity. The global models seem to be in good
agreement that some semblance of a warm core system will remain
after Walaka interaction with the extratropical low. Therefore, the
current forecast maintains Walaka as a tropical cyclone through 96
hours. It would not be surprising if the system becomes
extratropical sooner. The latest intensity forecast shows a slower
rate of weakening than most of the dynamical models, which is in
best agreement with the ECMWF through 48 hours, then aligns with the
SHIPS guidance afterward. The current intensity forecast is also
very close to the previous advisory package.
 
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  03/0900Z 18.1N 170.0W  115 KT 130 MPH
 12H  03/1800Z 20.4N 169.2W  110 KT 125 MPH
 24H  04/0600Z 23.9N 167.8W  105 KT 120 MPH
 36H  04/1800Z 27.5N 167.1W   90 KT 105 MPH
 48H  05/0600Z 29.9N 167.4W   80 KT  90 MPH
 72H  06/0600Z 33.5N 165.0W   60 KT  70 MPH
 96H  07/0600Z 41.5N 158.5W   50 KT  60 MPH
120H  08/0600Z 51.0N 146.0W   30 KT  35 MPH...POST-TROP/EXTRATROP
 
$$
Forecaster Houston
 
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