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Tropical Storm Olivia Discussion Number  45
NWS Central Pacific Hurricane Center Honolulu HI   EP172018
1100 AM HST Tue Sep 11 2018
 
The exposed low level circulation center (LLCC) of Olivia has been 
evident on visible satellite imagery this morning, outrunning the 
remaining deep convection sheared well to the east of the center. 
The surface dropsonde pressures from the Air Force Reserve
Hurricane Hunters were both 1007 mb, but these were a bit displaced
from the LLCC. The maximum SFMR winds were 45 kt in the northeast
quadrant, and so the initial intensity has been set to 50 kt. 

As we often see when the LLCC definitively seperates from the deep
convection, the motion can change rather drastically. The initial
motion estimate is 270/15 but the short term motion appears to be
even faster. Although the dynamical model track forecast guidance
remains tightly clustered, the motion of the LLCC actually appears
to be best in line with the TABS. Although the forecast philosophy
has not changed overall, I have sped up the forecast track and
shifted it to the right slightly in deference to the initial motion,
now a blend between the tightly packed dynamical consensus and TABS.
This change to the track and speed necessitates the issuance of a 
Tropical Storm Warning for Kauai. Seeing as how the wind field on 
the south side of Olivia is rather compact, it is possible we may
be able to discontinue the Tropical Storm Warning for the Big
Island later today if the westward motion continues.

The increasing shear over Olivia makes reintensification in the
near term quite unlikely, and the intensity forecast follows the
tightly clustered guidance. New deep convection may begin to form
near the center in 48 hours or so as an cold core upper low develops
to the north of Olivia and digs southwest. This may halt the
weakening trend, but at this point the cyclone is expected to lose
tropical characteristics or become subtropical.

 
Key Messages:
 
1. Although Olivia is expected to move over the islands as a
tropical storm, it could 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. It is important to not focus on the exact forecast track
and intensity when planning for Olivia. Regardless of the track
that Olivia takes as it approaches the islands, significant impacts
can be expected 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  11/2100Z 21.6N 152.3W   50 KT  60 MPH
 12H  12/0600Z 21.4N 155.0W   45 KT  50 MPH
 24H  12/1800Z 20.7N 157.6W   40 KT  45 MPH
 36H  13/0600Z 20.0N 160.6W   40 KT  45 MPH
 48H  13/1800Z 19.5N 163.2W   35 KT  40 MPH
 72H  14/1800Z 19.6N 167.7W   35 KT  40 MPH
 96H  15/1800Z 20.6N 170.8W   35 KT  40 MPH
120H  16/1800Z 21.5N 175.2W   25 KT  30 MPH...POST-TROP/REMNT LOW
 
$$
Forecaster R Ballard
 
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