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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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