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Hurricane Walaka Discussion Number  11
NWS Central Pacific Hurricane Center Honolulu HI   CP012018
1100 PM HST Mon Oct 01 2018
 
Walaka continues to display a warm well defined eye surrounded by a 
ring of -65 to -85C cloud tops. The presentation in geostationary 
satellite imagery has changed very little since the previous 
advisory, with perhaps a bit of an improvement in organization over 
the past hour. The most recent morphed microwave imagery from UW-
CIMSS indicates that Walaka may be going through an eyewall 
replacement cycle, so the down trend seen in the overall satellite 
presentation that began late Monday afternoon, may only be 
temporary. The latest intensity estimates from PHFO, SAB, JTWC all 
came in at 6.5 (127 knots) while ADT was 6.8 (135 knots). Given 
several satellite images Monday afternoon around 02/00Z showing T 
numbers of 7.0 (140 knots), and the likelihood that an eyewall 
replacement cycle is ongoing, the initial intensity was held at 140 
knots for this advisory. The initial motion was set at 330/07 knots.

A deep north Pacific upper level low in the vicinity of 30N 170W 
will draw Walaka northward over the next several days, before 
another sharp upper trough shifting across the north Pacific picks 
the tropical cyclone up and shifts it off to the northeast. Overall 
the guidance envelope remains fairly tightly clustered through the 
forecast period. The official forecast remains very close to that
of the previous advisory and remains closely aligned with the GFEX, 
TVCN, HCCA consensus guidance.

The environment surrounding Walaka remains conducive for additional 
intensification during the next 24 to 36 hours. The tropical
cyclone will remain within a deep moist airmass, with low vertical
wind shear, and sea surface temperatures between 84 to 86
Fahrenheit. Eyewall replacement cycles will likely lead to
fluctuation in intensity through this time frame, so the intensity
forecast shows little intensity change through 36 hours. Beyond 36
hours, vertical wind shear will increase, drier mid-level air will
begin to get wrapped into the cyclone, while sea surface
temperatures become marginal and even unfavorable. As a result,
Walaka should begin to weaken on Wednesday, with rapid weakening
then expected through the end of the forecast period. The official
forecast was not changed much from the previous advisory, and
remains above all guidance through 36 hours and then trends closer
to a blend of the statistical and dynamical models thereafter. 

The forecast track will take Walaka near Johnston Island on
Tuesday, so the Hurricane Warning remains in effect for this
location. The forecast track also takes the hurricane across the
Papahanaumokuakea Marine National Monument between French Frigate
Shoals and Laysan Island late Wednesday. Thus, a Hurricane Watch
remains in effect for the region from Nihoa to Maro Reef.
 
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  02/0900Z 13.7N 170.0W  140 KT 160 MPH
 12H  02/1800Z 15.1N 170.3W  140 KT 160 MPH
 24H  03/0600Z 17.3N 170.3W  140 KT 160 MPH
 36H  03/1800Z 20.2N 169.4W  135 KT 155 MPH
 48H  04/0600Z 23.5N 168.0W  115 KT 130 MPH
 72H  05/0600Z 29.8N 167.3W   80 KT  90 MPH
 96H  06/0600Z 32.5N 164.8W   65 KT  75 MPH
120H  07/0600Z 40.2N 157.7W   50 KT  60 MPH
 
$$
Forecaster Jelsema
 
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