WTPA41 PHFO 031523

TCDCP1



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