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Hurricane Walaka Discussion Number  18
NWS Central Pacific Hurricane Center Honolulu HI   CP012018
500 PM HST Wed Oct 03 2018
 
Walaka continues to show the effects of strong southwesterly
vertical shear, up to 47 kt at 0000 UTC from UW-CIMSS. The eye is no
longer visible in satellite imagery and has a very lopsided
appearance in the cirrus outflow, which is barely covering the low
level center of circulation.  In fact, recent visible imagery from
Himawari-8 shows what appears to be the southwest edge of the low
level circulation center becoming partially exposed, as the
southwest edge of the central dense overcast has occasionally pushed
even further to the northeast. This signals a weakening trend, which
has continued through the afternoon hours. The current intensity has
been lowered to 110 kt, following the downward trend in the Dvorak
estimates of 5.5/102 kt from all three fix agencies. This agrees
with the latest available UW-CIMSS ADT of 5.8/110 kt. 

Walaka has continued accelerating toward the north-northeast
this afternoon, with an initial motion for this advisory of 020/19
kt. With the low level cloud center (LLCC) possibly lagging behind
the upper level cloud features, the potential exists for a forward
speed correction with a good microwave data pass or if the LLCC does
finally become more visible on satellite. For now, the forecast is
for steady north-northeast motion overnight into early Thursday as
Walaka transits and exits the Papahanaumokuakea Marine National
Monument. A deceleration is expected Thursday night and Friday as
Walaka interacts with the deep cutoff cold core low pressure to its
north. Slight track forecast adjustments were made in the Friday
time frame toward the model consensus, which has trended further
west as it slows down during the interaction with the cold core low.
Late Friday, another mid latitude trough moving along in the
westerlies picks up Walaka and accelerates it off to the northeast
Saturday, as it becomes extratropical.
 
With continued strong vertical wind shear into Thursday and waters
dropping to 27 degrees C late tonight, Walaka will likely experience
a more rapid weakening trend in intensity tonight and Thursday,
dropping below major hurricane status within 12 hours. By later 
Thursday, the vertical wind shear is expected to relax, but
weakening is forecast to continue due to cooler SSTs in the 24 to
25 degree C range. The intensity forecast reflects the current
trends and closely follows the statistical and consensus dynamical
guidance.   
 
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  04/0300Z 23.1N 167.9W  110 KT 125 MPH
 12H  04/1200Z 25.9N 167.1W   95 KT 110 MPH
 24H  05/0000Z 29.2N 167.2W   75 KT  85 MPH
 36H  05/1200Z 31.3N 167.4W   60 KT  70 MPH
 48H  06/0000Z 34.0N 165.8W   50 KT  60 MPH
 72H  07/0000Z 44.0N 158.0W   40 KT  45 MPH...POST-TROP/EXTRATROP
 96H  08/0000Z...DISSIPATED
 
$$
Forecaster Brenchley
 
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