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 737 
 WTPA45 PHFO 091502
 TCDCP5
  
 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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