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Tropical Storm Ema Discussion Number   3
NWS Central Pacific Hurricane Center Honolulu HI   CP012019
500 PM HST Sat Oct 12 2019
 
The deep convection that had been over the low-level circulation 
center (LLCC) of Ema overnight and this morning has now been
shunted to the northeast, due to southwesterly vertical wind shear
near 25 kt. Latest GOES-17 high-resolution 1-minute imagery reveals
an increasingly exposed LLCC about 150 miles southwest of the
convection associated with a well developed mid-level center. An
ASCAT-C pass around 2100Z validated the 45 kt initial intensity used
in the previous advisory, and was also used to fine tune wind radii
for this forecast. Given these data, the initial intensity estimate
for this advisory has been lowered to 40 kt. 

With the cyclone becoming increasingly shallow, the primary
steering mechanism is a surface high centered far to the northeast,
and the initial motion estimate for this advisory is 310/10 kt. This
general motion is expected until dissipation occurs. With Ema now
north of a mid- and upper-level ridge axis, continued strong
southwesterly vertical wind shear will likely preclude significant
convection from persisting over the center, and a steady spin-down
is expected. Given this forecast philosophy, Ema is expected to
become a post-tropical remnant low within 24 hours before
dissipating shortly thereafter. The updated track and intensity
forecasts are supported by most of the reliable dynamical models. 

Given uncertainties associated with the rate of weakening and 
eventual path of Ema, a Tropical Storm Watch remains posted for 
portions of the Papahanaumokuakea Marine National Monument. 
  
  
FORECAST POSITIONS AND MAX WINDS
 
INIT  13/0300Z 21.7N 164.5W   40 KT  45 MPH
 12H  13/1200Z 22.7N 165.9W   35 KT  40 MPH
 24H  14/0000Z 24.6N 167.6W   30 KT  35 MPH...POST-TROP/REMNT LOW
 36H  14/1200Z...DISSIPATED
 
$$
Forecaster Birchard
 
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