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Tropical Storm Olivia Discussion Number 47
NWS Central Pacific Hurricane Center Honolulu HI EP172018
1100 PM HST Tue Sep 11 2018
Olivia's low level circulation center (LLCC) continues to be
exposed, with deep convection primarily located in the eastern
semicircle due to strong westerly vertical wind shear. Subjective
Dvorak current intensity estimates from PHFO/SAB/PGTW ranged from
2.0/30 kt to 3.0/45 kt. A blend of this data and an earlier ASCAT
pass support lowering the initial intensity to 40 kt for this
advisory.
The motion has been very erratic over the past 12 to 18 hours, and
although unclear as to why, it appears to have been modulated by
pulses in deep convection. When Olivia accelerated westward this
morning, associated deep convection had dissipated, allowing the
LLCC to be steered by the low-level trade winds. When deep
convection redeveloped this afternoon, the forward motion slowed
markedly, allowing a deeper-layer flow to lead to a slower forward
speed. The motion estimate for this advisory is 250/7 kt.
Erratic motion is likely to continue overnight as Olivia encounters
terrain, but a general west-southwest motion is expected, with an
increase in forward speed. If Olivia's LLCC survives the passage
near the island terrain, the center is expected to continue moving
toward the west-southwest through 48 hours. A more westward motion
is expected to begin by 72 hours and beyond as the deep layer ridge
west of Olivia weakens and an mid-level low digs southwest toward
the cyclone.
Our intensity forecast operates under the assumption that the LLCC
will be intact after emerging to the southwest of Maui and the Big
Island. If this occurs, gradual weakening is expected to continue
in line with all the guidance, which shows moderate to strong shear
continuing through the forecast period. Olivia is still expected to
become a remnant low within 72 hours, with dissipation expected by
day 5, but there is a decent chance this will happen even sooner.
Key Messages:
1. Although Olivia is weakening, flooding rainfall, high surf,
and damaging winds are expected in the warning area. Significant
impacts can occur well away from the center, especially when
considering that the mountainous terrain of Hawaii can produce
localized areas of strongly enhanced wind gusts and rainfall.
FORECAST POSITIONS AND MAX WINDS
INIT 12/0900Z 20.8N 154.6W 40 KT 45 MPH
12H 12/1800Z 20.2N 156.7W 40 KT 45 MPH
24H 13/0600Z 19.8N 159.3W 35 KT 40 MPH
36H 13/1800Z 19.3N 161.8W 30 KT 35 MPH
48H 14/0600Z 19.0N 164.4W 30 KT 35 MPH
72H 15/0600Z 19.5N 170.0W 30 KT 35 MPH...POST-TROP/REMNT LOW
96H 16/0600Z 21.0N 174.5W 30 KT 35 MPH...POST-TROP/REMNT LOW
120H 17/0600Z...DISSIPATED
$$
Forecaster Birchard
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