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 WTPA45 PHFO 121502
 Tropical Storm Olivia Discussion Number  48
 NWS Central Pacific Hurricane Center Honolulu HI   EP172018
 500 AM HST Wed Sep 12 2018
 An explosive overnight development of thunderstorms in Olivia's 
 eastern semicircle have since moved over the low level circulation 
 center (LLCC), despite westerly vertical wind shear near 25 kt. 
 Subjective Dvorak current intensity estimates ranged from 2.0/30 kt 
 to 2.5/35 kt this time around, but velocity data from the WSR-88D
 on Molokai indicate 50 kt winds at 5000 feet, and 45 kt at 10000
 feet. Using reduction factors typically applied to aircraft data,
 this supports a surface wind estimate of 40 kt. 
 Olivia's motion over the past 18 hours has been erratic, and 
 strongly modulated by the amount of associated deep convection. A 
 faster motion toward the west-southwest was observed when
 convection dissipated yesterday, with a slower forward speed toward
 the west-northwest observed with the deeper convection. This
 is due to the vertical wind shear, with the exposed low cloud swirl
 steered by low-level trade winds, while the deep convection allows
 Olivia's motion to be increasingly affected by the westerly flow
 aloft. With the persistent overnight convective burst, the initial
 motion estimate for this advisory is estimated to be 280/10 kt. 
 In the short term, Olivia is expected to move toward the west. 
 However, the expectation is that the deep convection will wane
 later this morning, and Olivia will make a turn toward the
 west-southwest by this afternoon. After emerging to the west of Maui
 County this evening, the expectation is that terrain interaction and
 increasing vertical wind shear will prevent deep convection from
 persisting over the center. A motion toward the west-southwest is
 then expected through 36 hours, with the assumption that the LLCC
 will be intact after emerging to the southwest of Maui County. GFS
 guidance indicates dissipation within 48 hours, while the ECMWF
 carries a surface low through day 5. The official forecast splits
 the difference, with Olivia devolving to a post-tropical remnant low
 by day 3 before dissipation on day 5.
 Key Messages: 
 1. 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. 
 INIT  12/1500Z 21.2N 155.7W   40 KT  45 MPH
  12H  13/0000Z 20.6N 157.6W   40 KT  45 MPH
  24H  13/1200Z 20.0N 160.4W   35 KT  40 MPH
  36H  14/0000Z 19.6N 163.1W   30 KT  35 MPH
  48H  14/1200Z 19.6N 166.0W   30 KT  35 MPH
  72H  15/1200Z 20.5N 171.5W   30 KT  35 MPH...POST-TROP/REMNT LOW
  96H  16/1200Z 21.0N 177.0W   30 KT  35 MPH...POST-TROP/REMNT LOW
 120H  17/1200Z...DISSIPATED
 Forecaster Birchard
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