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Tropical Storm OLIVIA

Tropical Storm Olivia Discussion Number  50
NWS Central Pacific Hurricane Center Honolulu HI   EP172018
500 PM HST Wed Sep 12 2018
Persistent southwesterly vertical wind shear of about 35 kt and
earlier interaction with the terrain of Maui County are weakening
Olivia. A diminishing amount of deep convection is now displaced
over 75 nautical miles to the northeast of the center, which has
become completely exposed, and velocity data from the Molokai
WSR-88D radar have declined over the islands this afternoon.
Subjective Dvorak current intensity estimates ranged from 2.0/30 kt
from SAB and JTWC to 2.5/35 kt at HFO. Thus, the initial intensity
will be lowered to 35 kt. 

The erratic motion of Olivia is expected to stabilize overnight. The
center accelerated westward in the low level trade wind flow, with
the initial motion nearly doubling to west-southwest (255 degrees)
at 17 kt. A general west-southwest motion with a slight loss of
forward speed will occur into Friday as Olivia is steered mainly by
the low-level trade wind flow. Olivia will then turn toward the
west-northwest as the system increasingly interacts with the upper
low responsible for the wind shear. The track forecast includes an
increase in forward speed and significant shift to the south
compared to the prior advisory in the short term, with little change
thereafter. The track forecast lies near TVCE and HCCA and is near
the middle of the guidance envelope, which is rather tightly
clustered through 48 hours, then has increasing spread beyond.

Olivia is expected to continue weakening. The system is hanging on
to tropical storm status, and given the persistent vertical wind
shear and displacement of the deep convection, Olivia is expected to
become a tropical depression by tonight or early Thursday, then
become a post-tropical remnant low on Thursday night or Friday. This
could occur sooner if deep convection fails to redevelop near the
center of Olivia. The intensity forecast is closest to SHIPS. Some
guidance members are intensifying Olivia beyond 72 hours as it
potentially moves under the core of the upper low, but the forecast
assumes that Olivia will not survive as a tropical cyclone long
enough for this to occur.

Due to the weakening trend, acceleration, and southward shift of the
track, tropical-storm-force winds have cleared Maui County and Oahu.
As a result, the Tropical Storm Warning for these islands has been
INIT  13/0300Z 20.1N 159.0W   35 KT  40 MPH
 12H  13/1200Z 19.7N 161.3W   30 KT  35 MPH
 24H  14/0000Z 19.4N 164.0W   30 KT  35 MPH
 36H  14/1200Z 19.5N 166.8W   30 KT  35 MPH...POST-TROP/REMNT LOW
 48H  15/0000Z 19.8N 169.2W   30 KT  35 MPH...POST-TROP/REMNT LOW
 72H  16/0000Z 21.2N 174.0W   25 KT  30 MPH...POST-TROP/REMNT LOW
 96H  17/0000Z...DISSIPATED
Forecaster Wroe