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Tropical Storm Flossie Discussion Number  25
NWS Central Pacific Hurricane Center Honolulu HI   EP072019
500 AM HST Sat Aug 03 2019
 
Flossie doesn't have the most impressive satellite signature this 
morning, but deep convection continues to develop close to where
the low-level circulation center (LLCC) is suspected to be.
Subjective and objective Dvorak intensity estimates have changed
little, and range from 2.0 to 3.0, with an average of the estimates
from PHFO/SAB/PGTW/UW-CIMSS yielding an intensity estimate of 35-40
kt at best. However, there has been little overall change in the
satellite appearance since the last advisory, when an ASCAT pass
indicated 50 kt in the northern semicircle around 07Z. With that
data in mind, the initial intensity estimate remains 50 kt. 

Finding and tracking Flossie's obscured LLCC remains a challenge, 
but it is estimated to be on the western edge of the deep 
convection, supported by a timely 1050Z GCOM pass. The initial 
motion estimate for this advisory is 285/12 kt, which represents a 
slowing in forward speed over the past 24 hours. Flossie is
expected to move toward the west-northwest over the next 48 hours,
steered by a low- to mid-level ridge centered to the north. On days
3 and 4, Flossie will round the western edge of the ridge, and
Flossie will turn toward the northwest, with a slowing in forward
speed. Model spread increases at that time, as is typically the case
with recurving cyclones. The HWRF/HMON and COAMPS-TC indicate a
track closer to the Hawaiian islands on the left side of the
guidance envelope, while ECMWF and it's ensemble mean are on the
right side of the envelope. Although the official forecast leans
toward the high-performing ECMWF, it was nudged southward in the
short term toward the HCCA, with the later forecast periods
essentially an update of the previous track forecast.

Although the environment in which Flossie is currently embedded is
not conducive for a hurricane, it is marginally supportive of a
tropical storm. Low- to mid-level easterly flow and relatively light
winds aloft are allowing the LLCC to remain in relative proximity to
the deep convection, despite vertical wind shear values near 20 kt.
In about 36-48 hours, Flossie will arrive in an area where westerly
vertical wind shear increases to 30-40 kt, and this unrelenting
shear will lead to the demise of Flossie, especially as it moves
over cooler water in the later forecast periods. The official
forecast closely follows trends presented by SHIPS and the intensity
consensus IVCN, with dissipation expected by the end of the forecast
period. 
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  03/1500Z 18.6N 143.5W   50 KT  60 MPH
 12H  04/0000Z 19.0N 145.3W   45 KT  50 MPH
 24H  04/1200Z 19.5N 147.8W   40 KT  45 MPH
 36H  05/0000Z 19.8N 150.1W   35 KT  40 MPH
 48H  05/1200Z 20.4N 152.3W   35 KT  40 MPH
 72H  06/1200Z 23.4N 155.8W   30 KT  35 MPH
 96H  07/1200Z 26.0N 157.5W   25 KT  30 MPH...POST-TROP/REMNT LOW
120H  08/1200Z...DISSIPATED
 
$$
Forecaster Birchard
 
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