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Hurricane Olivia Discussion Number  37...Corrected
NWS Central Pacific Hurricane Center Honolulu HI   EP172018
1100 AM HST Sun Sep 09 2018

Correction to 2nd paragraph to include mention of ongoing synoptic
reconnaissance mission.

There are conflicting signals in the aircraft reconnaissance data
and the satellite imagery this morning. Over the past few hours, a
persistent eye feature has redeveloped and deep convection has
been blowing up around the center. In fact, Dvorak Data-T numbers
climbed back up to 4.5 from all 3 satellite fix agencies. However,
the highest flight level wind was only 65 kt, and the SFMR winds
were even lower. Given Olivia's recent improved presentation on
satellite and a central dropsonde pressure of 988 mb, I would be
hard-pressed to lower the intensity below hurricane strength, and
decided instead to leave the current intensity at 65 kt, but this is
somewhat uncertain and may be generous. 

The initial motion estimate is 270/12. The forecast philosophy has
not changed, although the devil is in the details. Olivia is moving
to the south of a deep layer ridge which is building westward in
tandem with the tropical cyclone. Stronger ridging is expected to
develop west of Olivia in about 48 hours, sending the system on a
slightly more south of due west, or west-southwest track. The
consensus guidance remains fairly tightly clustered and changed
little with this advisory. However, there are some plausible
outliers, like the ECMWF which is on the north side of the guidance
and has actually shifted a bit northward once again. The GFS remains
on the southern side of the guidance spread. This uncertainty speaks
to the need to not focus on the exact forecast track as Olivia
moves across the islands. The U.S. Air Force Reserve Hurricane
Hunters are currently flying another synoptic mission to better
assess the steering flow around Olivia. 

Olivia is slowly moving toward warmer, though still marginal, sea
surface temperatures and is in an environment of weak shear.
This is expected to maintain intensity through the next 36 hours,
perhaps with additional fluctuations. Shear is expected to start
increasing over the tropical cyclone in 36 to 48 hours as an upper
level trough north of the main Hawaiian Islands builds south. This
should start to impart a weakening trend, which will be gradual at
first, then more rapid in the days 3-5 period. Our intensity
forecast remains on the higher side of a tightly clustered guidance
envelope.

 
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 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  09/2100Z 21.7N 145.1W   65 KT  75 MPH
 12H  10/0600Z 21.7N 146.7W   65 KT  75 MPH
 24H  10/1800Z 21.7N 148.5W   65 KT  75 MPH
 36H  11/0600Z 21.4N 150.5W   65 KT  75 MPH
 48H  11/1800Z 21.1N 152.5W   60 KT  70 MPH
 72H  12/1800Z 20.2N 157.1W   50 KT  60 MPH
 96H  13/1800Z 19.2N 162.3W   40 KT  45 MPH
120H  14/1800Z 19.6N 167.3W   30 KT  35 MPH
 
$$
Forecaster R Ballard
 
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