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Hurricane Olivia Discussion Number  41
NWS Central Pacific Hurricane Center Honolulu HI   EP172018
1100 AM HST Mon Sep 10 2018
 
Olivia still has a very well defined low level circulation center, 
albeit with a somewhat asymmetric wind field. Air Force Reserve 
Hurricane Hunters confirmed what the 1623 UTC SSMIS and 1849 UTC
GMI passes showed, that the system lacks a well-organized
convective core. Recent visible satellite images are showing new
convective bands developing on the east side of the circulation
center, however. The initial intensity was lowered to 65 kt based on
the reconnaissance data. 

The initial motion is estimated to be 270/8. There is no change to 
the forecast track philosophy for this package, as Olivia is
steered toward the west by a deep layer ridge to the west through
north of the cyclone. This will continue to impart a just south of
due west motion for the next 72 hours. The consensus models remain
tightly clustered and have not budged. Our track forecast continues
to reflect a blend of the consensus models and the ECMWF. It is
worth noting that the last four runs of the GFS have trended north,
and is now coming into much better agreement with the guidance
consensus as well. After 72 hours, an upper level low will approach
Olivia from the north and begin to pull the tropical cyclone on a
more west-northwestward motion. Even at 120 hours, the guidance is
fairly tightly clustered, and our track forecast remains very close
to TVCN, HMON, HWRF, and FSSE.

Olivia remains over marginal sea surface temperatures of about 
26.5C, but is approaching the edge of a weak shear environment, 
according the UW-CIMSS analysis. The SSTs will be warming along the 
forecast track, but the shear will begin gradually increasing soon. 
Without a strong eyewall or core, weakening should begin fairly
soon after the shear increases. The intensity forecast continues to 
maintain Olivia as a hurricane through 12 hours, followed by slow 
but steady weakening thereafter. Our forecast is on the higher end 
of the guidance envelope through the first few days, but it is 
possible that weakening could occur faster due to shear effects and 
interaction of the circulation with island terrain.
 
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 east of Kauai 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  10/2100Z 21.7N 148.7W   65 KT  75 MPH
 12H  11/0600Z 21.5N 150.1W   65 KT  75 MPH
 24H  11/1800Z 21.3N 152.2W   60 KT  70 MPH
 36H  12/0600Z 21.0N 154.4W   55 KT  65 MPH
 48H  12/1800Z 20.6N 156.8W   50 KT  60 MPH
 72H  13/1800Z 20.1N 161.8W   40 KT  45 MPH
 96H  14/1800Z 20.3N 167.0W   35 KT  40 MPH
120H  15/1800Z 21.4N 172.2W   30 KT  35 MPH
 
$$
Forecaster R Ballard
 
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