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Hurricane Olivia Discussion Number  36
NWS Central Pacific Hurricane Center Honolulu HI   EP172018
500 AM HST Sun Sep 09 2018
 
Olivia remains poorly organized early this morning. There continue
to be hints of an eye in satellite imagery, but the feature has not
been consistent for any length of time. A timely AMSR microwave
image from 1140z confirms the initial location used for this
advisory, plus it showed a closed eyewall structure a few hours
ago. The latest subjective Dvorak current intensity estimates from
the satellite fix agencies ranged from 4.0/65 kt at PHFO to 3.5/55
kt at SAB and JTWC. The latest UW-CIMSS ADT estimate is also 3.5/55
kt. The U.S. Air Force Reserves 53rd Weather Reconnaissance Squadron
will be conducting missions in and around Olivia later today. The
first mission, which will depart from Oahu shortly, will be making
direct measurements in Olivia. This will help us determine the
track, intensity, and size of the system. The second mission by the
53rd will sample the environment around Olivia to provide valuable
data for improved initialization of the forecast models that will
run later today. This is expected to improve the track and intensity
forecasts as Olivia approaches the Hawaiian Islands this week. Since
there is so much uncertainty for the moment in the initial
intensity, we will only weaken Olivia to a 65 kt hurricane for this
advisory.
 
Olivia continues to move due west, and 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.
Olivia is expected to continue moving westward at a slightly slower
forward speed during the next 36 hours, since the ridging is
forecast to build westward in tandem with the tropical cyclone's
movement. Beyond 36 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, but has started to shift southward. As a
result, the latest forecast track has been nudged to the left from
days 2 through 4. This track still 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 remains in an environment with relatively weak vertical wind
shear, but it is moving over marginal sea surface temperatures
(SSTs) of 25.5C. The hurricane has likely already traversed the
coolest water along its track. Note that the Ocean Heat Content
(OHC) analysis from CIRA shows this parameter may increase starting
around 24 or 36 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 this week.
 
2.  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 winds and
rainfall, even well away from the tropical cyclone center.
 
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  09/1500Z 21.8N 143.9W   65 KT  75 MPH
 12H  10/0000Z 21.8N 145.5W   70 KT  80 MPH
 24H  10/1200Z 21.8N 147.6W   70 KT  80 MPH
 36H  11/0000Z 21.7N 149.4W   70 KT  80 MPH
 48H  11/1200Z 21.3N 151.2W   65 KT  75 MPH
 72H  12/1200Z 20.3N 155.5W   55 KT  65 MPH
 96H  13/1200Z 19.5N 160.0W   45 KT  50 MPH
120H  14/1200Z 19.5N 165.0W   35 KT  40 MPH
 
$$
Forecaster Houston
 
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