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Tropical Storm Hector Discussion Number  52
NWS Central Pacific Hurricane Center Honolulu HI   EP102018
1100 PM HST Sun Aug 12 2018
 
Hector's appearance has severely degraded according to satellite
imagery this evening. The low-level circulation center (LLCC) is
becoming almost entirely exposed, and the last area of deep
convection has nearly dissipated, leaving behind mainly cirrus
debris. This is not unexpected given the vertical wind shear of
11 to 14 kt from the south-southwest according to the latest
SHIPS and UW-CIMSS analyses. The most recent subjective Dvorak
intensity estimates are T3.5/55 knots from PHFO and SAB, and
T3.0/45 knots from JTWC based on a shear pattern. The UW-CIMSS ADT
estimate is T2.5/35 knots. Based on all of this guidance, we are
lowering the initial intensity to 55 knots for this advisory.

Since we can easily monitor the movement of the exposed LLCC in
satellite imagery, the initial motion is set at 295/15 knots. The
track forecast has been adjusted slightly from the previous
one. Surprisingly, the latest model guidance remains tightly
clustered through 72 hours, with the spread in the forecast tracks
increasing on Days 4 and 5. Hector is expected to continue on a
west-northwest track along the eastern periphery of a retrograding
upper-level low located just west of the International Date Line
near Longitude 173E. As this low aloft continues to move west, an
upper level ridge is forecast to build north of the Hector. This
will likely keep the tropical storm moving toward the
west-northwest during the next 48 hours. A gradual turn toward the
northwest is expected in around 72 hours, followed by a turn
toward the north on days 4 and 5, as Hector rounds the western
end of the ridge. The latest forecast track remains very close to
the consensus guidance. Note that since the system is sheared, the
forecast track is also close to the TABS through 48 hours. Based on
the latest forecast track, Hector will likely cross the
International Dateline into the Northwestern Pacific on Monday.

The latest intensity forecast is very close to the previous forecast
package. The forecast indicates additional weakening is expected
during the next 12 hours. Based on the current appearance and the
continuing southwesterly shear of 10 to 15 knots, it is likely this
will occur. The forecast guidance continues to show the shear may
relax within 18 to 24 hours, but the system will likely be weaker by
this time and will be moving over cooler sea surface temperatures.
The intensity guidance is in fairly good agreement through 36 hours,
so confidence during this portion of the forecast is fairly good.
Most of the intensity guidance levels off during the 36 through 48
hour time frame, while the SHIPS guidance and GFS indicate some
unrealistic strengthening. The main weakening trend is on days 3 and
4. In addition, Hector is forecast to transition to an extratropical
gale low in about 96 hours.

Since the current track continues to shift more toward the west, the
Tropical Storm Watch has been discontinued for Kure Atoll and Midway
Atoll. Note that large breaking waves are still likely to persist
along the Northwestern Hawaiian Islands from tonight into Monday due
to the southeast swell generated by Hector.
 
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  13/0900Z 24.9N 178.8W   55 KT  65 MPH
 12H  13/1800Z 25.9N 178.9E   50 KT  60 MPH
 24H  14/0600Z 27.0N 175.9E   50 KT  60 MPH
 36H  14/1800Z 28.0N 172.8E   50 KT  60 MPH
 48H  15/0600Z 29.2N 169.8E   50 KT  60 MPH
 72H  16/0600Z 32.0N 164.5E   45 KT  50 MPH
 96H  17/0600Z 36.0N 162.5E   35 KT  40 MPH
120H  18/0600Z 42.0N 164.5E   35 KT  40 MPH...POST-TROP/EXTRATROP
 
$$
Forecaster Houston
 
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