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Tropical Storm Olivia Discussion Number  46
NWS Central Pacific Hurricane Center Honolulu HI   EP172018
500 PM HST Tue Sep 11 2018
 
Olivia's low level circulation center (LLCC) continues to outrun
the bands of deep convection now well to the east of the center.
Without any new deep convection near the center, the wind field
continues to gradually spin down. However, the 53rd Weather
Reconnaissance Squadron found SFMR winds of 42 kt in the northeast
quadrant. Thus, the current intensity has been lowered to 45 kt for
this advisory. This also agrees well with an earlier 1939 UTC ASCAT
pass that covered part of the tropical cyclone. 

The motion has been very erratic today. As the LLCC decoupled from 
the deep convection, it accelerated rapidly westward. Since about 
2000 UTC, this motion has been quite a bit slower and toward the 
southwest. Averaging this out to a representative motion gives 
260/13. Erratic motion is likely to continue overnight as the now 
shallow circulation of Olivia encounters terrain, but a general
west-southwest motion is expected. If Olivia's LLCC survives the
passage near the island terrain (and this is a big if), the center
is expected to continue moving toward the west-southwest through 48 
hours. A more westward motion is expected to begin by 72 hours and 
beyond as the deep layer ridge west of Olivia weakens and an mid-
level low digs southwest toward the cyclone.

Our intensity forecast operates under the assumption that the low 
level circulation center will be intact after emerging to the 
southwest of Maui and the Big Island. If this occurs, gradual 
weakening is expected to continue in line with all the guidance 
which shows moderate to strong shear continuing through the
forecast period. Olivia is expected to become a remnant low within
72 hours, but there is a decent chance this will happen even
sooner. 

Key Messages:
 
1. As Olivia moves across the main Hawaiian Islands, it still bring
worse impacts than recent Hurricane Lane to some areas. Those
impacts could include flooding rainfall, damaging winds, and
large and dangerous surf.
 
2. Significant impacts can occur well away from the center. In
particular, the mountainous terrain of Hawaii can produce localized
areas of strongly enhanced wind gusts and rainfall.
 
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  12/0300Z 20.9N 154.2W   45 KT  50 MPH
 12H  12/1200Z 20.4N 156.4W   45 KT  50 MPH
 24H  13/0000Z 19.6N 158.9W   40 KT  45 MPH
 36H  13/1200Z 19.1N 161.7W   35 KT  40 MPH
 48H  14/0000Z 18.8N 164.7W   35 KT  40 MPH
 72H  15/0000Z 19.0N 169.0W   30 KT  35 MPH...POST-TROP/REMNT LOW
 96H  16/0000Z 19.8N 172.7W   30 KT  35 MPH...POST-TROP/REMNT LOW 
120H  17/0000Z 20.9N 176.0W   30 KT  35 MPH...POST-TROP/REMNT LOW
 
$$
Forecaster R Ballard
 
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