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Tropical Storm Walaka Discussion Number   2
NWS Central Pacific Hurricane Center Honolulu HI   CP012018
500 PM HST Sat Sep 29 2018
 
The satellite presentation of Walaka has not changed significantly 
since this morning. The banding feature to the east and south of the
center has become less distinct, though a large area of deep
convection has persisted near the center. Subjective Dvorak current
intensity estimates range from 2.0/30 kt out of JTWC to 2.5/35 kt
from HFO and SAB. The initial intensity will be held at 35 kt for
this advisory. 

Walaka continues to move toward the west (265 degrees) at 13 kt. A
deep ridge to the north will steer Walaka on a general westward
motion through Sunday, taking the cyclone well southwest of the main
Hawaiian Islands. Late Sunday through Monday night, Walaka will make
a gradual turn toward the northwest then north as a deep North
Pacific trough digs southward and steadily erodes the ridge. As a
result, Walaka will pass very close to, or over, Johnston Atoll as
early as Monday night and likely on Tuesday. The deep trough will
stall roughly along 171W longitude on Tuesday, and as interaction
with the trough increases, Walaka will accelerate northward on days
four and five. This should take the system across the
Papahanaumokuakea Marine National Monument. The track guidance
envelope is tightly clustered through 72 hours, with differences in
forward motion increasing thereafter. Through 72 hours, the track
forecast is essentially unchanged and lies near the middle of the
tightly clustered guidance envelope. On days four and five, the
forecast forward motion has been accelerated to follow the TVCE
and HMON, which are slower than the GFS and faster than the ECMWF.

Strengthening, possibly rapid, is expected through the next three
days. Walaka will remain under low vertical wind shear and over SSTs
of around 29C through at least Monday and likely into early Tuesday.
In this environment, the bulk of the intensity guidance shows rapid
intensification during the next 48 hours, and the SHIPS rapid
intensification guidance for Walaka remains well above the
climatological mean through 72 hours. On days four and five,
interaction with the deep trough will create increasing vertical
wind shear that should lead to weakening. The intensity forecast was
changed little from the prior advisory and is close to LGEM between
SHIPS and HMON, near the middle of the guidance envelope. Walaka is
forecast to become a hurricane by Sunday, and along the forecast
track, hurricane conditions could be experienced on Johnston Atoll
as early as Monday night.
 
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  30/0300Z 11.4N 160.5W   35 KT  40 MPH
 12H  30/1200Z 11.6N 162.7W   50 KT  60 MPH
 24H  01/0000Z 11.9N 165.4W   65 KT  75 MPH
 36H  01/1200Z 12.4N 167.5W   80 KT  90 MPH
 48H  02/0000Z 13.5N 168.8W   95 KT 110 MPH
 72H  03/0000Z 16.9N 169.6W  110 KT 125 MPH
 96H  04/0000Z 22.9N 168.3W   95 KT 110 MPH
120H  05/0000Z 30.1N 168.5W   70 KT  80 MPH
 
$$
Forecaster Wroe
 
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