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Tropical Storm Olivia Discussion Number  42
NWS Central Pacific Hurricane Center Honolulu HI   EP172018
500 PM HST Mon Sep 10 2018
 
Air Force Reserve Hurricane Hunters indicated that Olivia was on a 
slow weakening trend as they departed the tropical cyclone earlier 
this afternoon. Bursts of convection have been occurring, but an 
0058 UTC SSMI and 0155 UTC AMSU pass are showing disorganized 
banding mainly to the northeast of the center. This seems to 
indicate that Olivia is beginning to feel the effects of stronger 
shear. There was a fairly wide spread of satellite intensity 
estimates. However, used a blend of these along with the recent 
reconnaissance data to come up with the intensity estimate of 60 kt.

Olivia has been moving 280/9 over the last few hours. This slightly 
north-of-west motion may be due to the tropical cyclone beginning
to feel the effects of the increasing shear. All reliable track
guidance are unanimous in maintaining a westward motion overnight,
then a slightly south of due west motion is expected to begin in 12
to 24 hours, as a very strong deep layer ridge develops west of the
main Hawaiian Islands. Beyond 72 hours, an upper level low is
expected to develop to the north of Olivia and drop south. This
upper low is expected to impart a west-northwest motion on the
tropical cyclone, and in fact the two systems may merge in four to
five days, if enough of the low level circulation remains in the
face of strong shear.

Shear is expected to increase over the next 24 to 48 hours as
Olivia continues generally westward. Even though the sea surface 
temperatures warm to greater than 28C along the track beyond 48 
hours, the shear should allow weakening to continue. The intensity 
guidance has been backing off on the weakening trend some in the 3 
to 5 day time period, likely due to interaction with the upper low. 
Toward the end of the forecast period, Olivia may be starting to 
lose tropical characteristics. 
 
KEY MESSAGES:
 
1.  Resist the temptation to make comparisons between Hurricane
Lane and Hurricane Olivia. Although Lane was a stronger tropical
cyclone near the islands, it did not bring direct core impacts to
the state. In some areas, Olivia could bring significantly worse
impacts than were felt by Lane.
 
2.  It is important to not focus on the exact forecast track and
intensity when planning for Olivia. Persons on the main Hawaiian
Islands should finish their preparations for direct impacts from
this system starting as early as Tuesday night. Those impacts could
include intense flooding rainfall, damaging winds, and large and
dangerous surf.
 
3.  Regardless of the exact track and intensity that Olivia takes
as it approaches the islands, significant effects often extend far
from the center. In particular, the mountainous terrain of Hawaii
can produce localized areas of strongly enhanced wind gusts and
rainfall, even well away from the tropical cyclone center.
 
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  11/0300Z 21.9N 149.7W   60 KT  70 MPH
 12H  11/1200Z 21.9N 151.2W   55 KT  65 MPH
 24H  12/0000Z 21.6N 153.5W   50 KT  60 MPH
 36H  12/1200Z 21.2N 155.7W   50 KT  60 MPH
 48H  13/0000Z 20.7N 158.1W   45 KT  50 MPH
 72H  14/0000Z 20.1N 163.1W   40 KT  45 MPH
 96H  15/0000Z 20.7N 167.8W   35 KT  40 MPH
120H  16/0000Z 22.5N 173.5W   30 KT  35 MPH
 
$$
Forecaster R Ballard
 
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