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Tropical Storm Ema Discussion Number   1
NWS Central Pacific Hurricane Center Honolulu HI   CP012019
500 AM HST Sat Oct 12 2019

Recent satellite-derived wind data indicated that the area of low 
pressure far southwest of Hawaii had become better organized 
overnight. A 0826Z ASCAT pass showed a closed circulation along
with a broad area of 30 knot winds and a single 35 knot wind barb.
Based on this data and persistent deep convection over the
low-level circulation center through much of the night, advisories
have been initiated on newly formed Tropical Storm Ema. The initial
intensity will be set at 35 knots, which is in line with the ASCAT
data, and the initial motion will be set at 325/10 knots. 

Ema will be entering an increasingly unfavorable environment over 
the next couple days, with increasing west-southwesterly vertical 
wind shear and dry mid-level air. This should result in a more
shallow system driven by the low-level boundary layer flow. The
official forecast track is most closely in line with the ECMWF
solution which seems to have the best handle on the initial 
intensity and motion of the tropical cyclone. Ema is expected to 
track off to the northwest over the next couple days, and dissipate 
Sunday night. 

Although sea surface temperatures along the forecast track will 
remain conducive for intensification, the increasing vertical wind 
shear and dry mid-level air (which seems to be already affecting
Ema over the past couple hours), should result in little change in 
strength today and tonight. The official forecast weakens Ema into
a post-tropical remnant low on Sunday, with dissipation expected 
Sunday night. The intensity forecast is slightly below the guidance 
envelope through dissipation.  

Although Tropical Storm force winds are not expected to affect the 
northwest Hawaiian Islands, interests in the Papahanaumokuakea 
Marine National Monument should continue to monitor the progress of 
Ema. 
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  12/1500Z 20.0N 163.5W   35 KT  40 MPH
 12H  13/0000Z 21.3N 164.5W   35 KT  40 MPH
 24H  13/1200Z 22.6N 166.3W   35 KT  40 MPH
 36H  14/0000Z 24.5N 167.9W   30 KT  35 MPH...POST-TROP/REMNT LOW
 48H  14/1200Z...DISSIPATED
 
$$
Forecaster Jelsema
 
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