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Hurricane Olivia Discussion Number  35
NWS Central Pacific Hurricane Center Honolulu HI   EP172018
1100 PM HST Sat Sep 08 2018
 
Olivia remains poorly organized in infrared satellite imagery
this evening. There have been hints of an eye in some of this
imagery, but this feature is not persistent. The latest
subjective Dvorak current intensity estimates were 4.0/65 kt from
PHFO and SAB. Note that JTWC has only been doing fixes on this
system since around 0000z, so their 3.5/55 kt was unrepresentative,
since there is no valid MET available. The latest UW-CIMSS ADT
estimate was 4.1/67 kt. We will maintain the current intensity at
70 kt for this advisory.

Olivia is now moving due west, so the initial motion estimate is
270/14 kt. The hurricane is being steered to the south of a strong
deep layer ridge situated north through west of the system.
Little change in forward motion is expected during the next 2 days,
since the ridging is forecast to build westward in tandem with
Olivia. After 48 hours, the portion of the ridge to the west of
Olivia is forecast to build, which will likely shunt the tropical
cyclone on a more west-southwest motion. The track guidance remains
fairly tightly clustered, and this forecast is very similar to the
previous forecast track, which brings the center of Olivia across
the main Hawaiian Islands between 72 and 96 hours. A more westward
motion is expected to resume after Olivia's passage through the
islands, as the upper ridge retreats westward and the circulation
center becomes increasingly steered by the low-level trade wind
flow.
 
Olivia is in a very weak vertical wind shear environment, but it is
moving over marginal sea surface temperatures of 25.5C. The
hurricane has likely traversed the coolest water it was going to
encounter, but SSTs stay sub-27C until Olivia gets close to the
islands. Note that the Ocean Heat Content (OHC) analysis from CIRA
shows this parameter may increase starting around 36 or 48 hours, so
this may help Olivia maintain its intensity longer than is currently
forecast. However, vertical wind shear is expected to begin
increasing after 48 hours, which will likely result in a gradual 
weakening trend. Despite this trend, Olivia is forecast to remain a
strong tropical storm during 72 to 96 hours, which could cause
significant impacts in the main Hawaiian Islands. The latest
intensity forecast closely follows the previous advisory.
 
 
KEY MESSAGES:
 
1.  It is important to recognize that errors in both forecast track
and intensity, particularly at longer time ranges, can be large.
While it is too soon to determine the location and magnitude of the
worst impacts, all interests in Hawaii should continue to monitor
the progress of Olivia, and use this time to prepare for the
increasing likelihood of direct impacts from this system early next
week.
 
2.  Regardless of the exact track and intensity that Olivia takes
as it approaches the islands, significant effects often do extend
far from the center. In particular, the mountainous terrain of
Hawaii can produce localized areas of strongly enhanced winds and
rainfall, even well away from the tropical cyclone center.
 
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  09/0900Z 21.8N 142.5W   70 KT  80 MPH
 12H  09/1800Z 21.8N 144.3W   70 KT  80 MPH
 24H  10/0600Z 21.8N 146.6W   70 KT  80 MPH
 36H  10/1800Z 21.8N 148.7W   70 KT  80 MPH
 48H  11/0600Z 21.7N 150.6W   65 KT  75 MPH
 72H  12/0600Z 20.9N 154.3W   55 KT  65 MPH
 96H  13/0600Z 19.8N 159.0W   50 KT  60 MPH
120H  14/0600Z 19.6N 164.0W   40 KT  45 MPH
 
$$
Forecaster Houston
 
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