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Hurricane Olivia Discussion Number  38...Corrected
NWS Central Pacific Hurricane Center Honolulu HI   EP172018
500 PM HST Sun Sep 09 2018
 
Olivia has continued to exhibit an indistinct but persistent eye 
feature over the past several hours. A 2120 UTC AMSR2 and a 0050 UTC
SSMIS pass showed a partial eyewall, mainly in the southeastern
semicircle, along with what appears to be a developing banding
feature to the northeast and east of the center. The subjective
intensity estimates from SAB, JTWC, and PHFO were unanimous at 4.5,
and ADT gave a 4.3. Have maintained the current intensity of 65 kt
for now, pending more data from the next Air Force Reserve Hurricane
Hunter mission this evening.

Neglecting wobbles, Olivia is moving 270/10. This due west motion
is being induced by a deep layer ridge to the north and northwest
of the tropical cyclone. In 12 to 24 hours, the ridge is expected
to strengthen and build southward ahead of Olivia, forcing the
cyclone on a slightly slower and more south of due west motion that
will persist through about 96 hours. Unfortunately, the track
guidance actually shows slightly more spread for this cycle. The
ECMWF, Canadian, and NAVGEM models are on the northern side of the 
envelope, while the GFS now appears to be a southern outlier. The 
consensus guidance splits the difference and remained very close to 
the previous forecast. Thus, made very little change to the
forecast track. However, the spread in the guidance and resulting
uncertainty demonstrates the importance of not focusing too much on
the exact track as Olivia moves across the islands.  

There's also little change to the forecast thinking in terms of 
intensity. Sea surface temperatures will be marginal, but gradually 
increasing along the track as Olivia approaches the main Hawaiian 
Islands. Wind shear is expected to remain weak over the tropical 
cyclone through the next 24 hours, then begin gradually increasing, 
approaching 30 knots by 72 hours. All of the intensity guidance 
depicts weakening after 36 hours, but at somewhat different rates. 
Our forecast depicts Olivia weakening faster than HCCA and LGEM,
but not as fast as most of the consensus guidance, HMON, and SHIPS.

KEY MESSAGES: 

1.  It is important to not focus on the exact forecast track and 
intensity when planning for Olivia. Persons on all the main
Hawaiian Islands should continue preparing for the likelihood of
direct impacts from this system this week. Those impacts could
include intense flooding rainfall, damaging winds, large and
dangerous surf, and storm surge.

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  10/0300Z 21.7N 146.1W   65 KT  75 MPH
 12H  10/1200Z 21.7N 147.6W   65 KT  75 MPH
 24H  11/0000Z 21.5N 149.5W   65 KT  75 MPH
 36H  11/1200Z 21.2N 151.5W   65 KT  75 MPH
 48H  12/0000Z 20.9N 153.7W   60 KT  70 MPH
 72H  13/0000Z 19.9N 158.4W   50 KT  60 MPH
 96H  14/0000Z 19.3N 163.6W   40 KT  45 MPH
120H  15/0000Z 20.1N 168.8W   30 KT  35 MPH
 
$$
Forecaster R Ballard
 
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