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Hurricane Walaka Discussion Number  16...Corrected
NWS Central Pacific Hurricane Center Honolulu HI   CP012018
500 AM HST Wed Oct 03 2018
 
Walaka's eye became much more distinct overnight. In addition, the
cloud tops cooled significantly in the eyewall. Note that in the
last couple of hours, the northwestern eyewall is beginning to show
some signs of becoming more narrow. This may be due to increasing
vertical wind shear, as well interaction with an upper-level trough
located to the northwest of Walaka. Prior to this, some of the
satellite fix agencies showed intensification occurred early this
morning. The most recent subjective Dvorak current intensity
estimates were 6.5/127 kt from JTWC, 6.0/115 kt from PHFO, and
5.5/102 kt from SAB. The latest UW-CIMSS ADT estimate was 7.0/140
kt. Based on a blend of these estimates, we have increased Walaka's
initial intensity to 120 kt for this advisory.
 
Walaka has been accelerating toward the north-northeast overnight,
and the initial motion for this advisory is 015/15 kt. The primary
steering mechanism is the circulation around a vertically-stacked
low pressure area near 32N 170W. Therefore, Walaka is expected to
continue accelerating toward the north-northeast into tonight.
Once the hurricane gets closer to this extratropical feature, the
track guidance indicates its forward motion will slow during the 24
to 48 hour time period. The latest track forecast continues to show
a brief bend in the track toward the north-northwest, followed by
rapid acceleration toward the northeast between 48 and 96 hours. 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 through 36 hours, except for some minor increase in forward
motion. The track was adjusted to the left around 48 hours to more
closely follow the consensus guidance, which appears to be in
general agreement in regards to the interaction with the low. There
was little change in the track from the previous advisory during the
72 to 120 hour time periods.
 
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 by 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 72
hours. However, 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. It is in best
agreement with the ECMWF and GFS output. The current intensity
forecast is showing a somewhat faster weakening trend beyond 36
hours compared with the previous advisory package.
 
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  03/1500Z 19.6N 169.4W  120 KT 140 MPH
 12H  04/0000Z 22.2N 168.4W  110 KT 125 MPH
 24H  04/1200Z 25.9N 167.3W  100 KT 115 MPH
 36H  05/0000Z 29.0N 167.4W   85 KT 100 MPH
 48H  05/1200Z 30.7N 167.5W   75 KT  85 MPH
 72H  06/1200Z 35.0N 163.5W   55 KT  65 MPH
 96H  07/1200Z 44.5N 155.5W   45 KT  50 MPH...POST-TROP/EXTRATROP
120H  08/1200Z 53.0N 143.0W   30 KT  35 MPH...POST-TROP/EXTRATROP
 
$$
Forecaster Houston
 
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