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Tropical Storm Flossie Discussion Number  24
NWS Central Pacific Hurricane Center Honolulu HI   EP072019
1100 PM HST Fri Aug 02 2019
 
Despite Dvorak intensity estimates indicating that Flossie might be 
a tad weaker, and a somewhat unimpressive satellite appearance, the 
initial intensity estimate for this advisory was kept at 50 kt. 
Those winds are primarily located in the northern semicircle, where 
the gradient between Flossie and a low- to mid-level ridge to the 
north remains tight. A recently received ASCAT pass confirms this 
initial intensity, with a few 50 kt wind barbs noted in the
northern semicircle. 

Finding and tracking Flossie's LLCC is difficult as it is obscured 
by mid- and high-level clouds, and the initial motion estimate is a 
somewhat uncertain 290/15 kt. The LLCC is estimated to be southwest 
of the deep convection, due to westerly vertical wind shear on the 
order of 20 to 25 kt. Several microwave passes were received
between 02Z and 06Z, helping to locate the LLCC. The track forecast 
anticipates Flossie moving toward the west-northwest over the next
day or two, with a slight reduction in forward speed, steered by the
aforementioned ridge to the north. On days 3 and 4, Flossie will
round the western edge of the ridge, and a turn toward the northwest
is expected, with additional slowing in forward speed. The updated
track forecast is to the left of the previous due to a westward
shift in most of the guidance, with FSSE and CTCI now joining the
HWRF/HMON on the left side of the envelope. The updated track
forecast lies close to the ECMWF guidance, which has been the best
performer with Flossie.  

Flossie is expected to traverse over marginal SSTs through most of 
the forecast period, with cooler SSTs expected by day 5 as it gains 
latitude. Furthermore, vertical shear is expected to increase to 
above 30 knots after 48 hours, although a slight reduction is 
possible in the short term. Given these factors, statistical and 
dynamical intensity guidance depicts only gradual weakening in the 
short term, with a greater rate of weakening thereafter. The 
intensity forecast was changed little from the previous, but now 
indicates Flossie becoming a post-tropical remnant low on days 4
and 5, with dissipation expected soon thereafter. 
 
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  03/0900Z 18.3N 142.3W   50 KT  60 MPH
 12H  03/1800Z 18.9N 144.4W   45 KT  50 MPH
 24H  04/0600Z 19.5N 146.5W   45 KT  50 MPH
 36H  04/1800Z 19.8N 148.9W   40 KT  45 MPH
 48H  05/0600Z 20.5N 151.3W   35 KT  40 MPH
 72H  06/0600Z 22.7N 155.4W   30 KT  35 MPH
 96H  07/0600Z 25.6N 157.5W   25 KT  30 MPH...POST-TROP/REMNT LOW
120H  08/0600Z 29.0N 158.5W   25 KT  30 MPH...POST-TROP/REMNT LOW
 
$$
Forecaster Birchard
 
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