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Tropical Storm Flossie Discussion Number  20
NWS National Hurricane Center Miami FL       EP072019
1100 PM HST Thu Aug 01 2019

An 0646 UTC ASCAT-B overpass captured Flossie's entire tropical-
storm-force wind field and confirmed that the structure remains
asymmetric.  Combining the scatterometer data and conventional
infrared satellite images shows that Flossie's center is embedded
just within the southwestern edge of -70 degree Celsius cloud tops.
The initial intensity remains 60 kt, which is a blend of Dvorak CI
numbers from TAFB and SAB, and just above the 55 kt shown by the
ASCAT data (accounting for possible undersampling).

Flossie just won't slow down, as the initial motion is still
west-northwestward, or 285/16 kt.  The subtropical ridge to the
north remains strong, and this should keep Flossie on the west-
northwestward trajectory for the next 3 days, although the
track models insist that the current speed should decrease a bit.
After day 3, a deepening upper-level low north and northwest of the
Hawaiian Islands should cause Flossie to turn northwestward and
then northward on days 4 and 5.  The NHC official forecast depicts
such a scenario, but this is where the forecast has the most
uncertainty.  All of the global models and most of the consensus
models show Flossie recurving northeast of the Hawaiian Islands,
while the regional HWRF and HMON models, as well as the Florida
State Superensemble, are depicting a more southern solution with
less recurvature.  Despite these southern solutions, the new NHC
forecast is relatively unchanged from the previous one and is very
close to the HCCA and TVCX consensus aids.

Nearly steady shear of 15 kt and ocean temperatures around 27
degrees Celsius should keep Flossie's intensity relatively steady
for the next 12 hours or so.  After that time, deep-layer shear is
expected to steadily increase to at least 30 kt by 48 hours while
Flossie also moves over a relative minimum in sea surface
temperatures just under 26 degrees Celsius.  These factors are
likely to contribute to steady weakening, and there is relatively
little spread among the intensity models in showing this scenario.
The updated NHC intensity forecast has been lowered slightly from
the previous one and shows Flossie becoming a tropical depression in
4 days.

On the forecast track, Flossie will be moving into the central
Pacific basin in 12-24 hours, at which point the Central Pacific
Hurricane Center will assume forecast responsibilities.  In the
meantime, users should continue to consult local forecasts from the
National Weather Service Forecast Office in Honolulu, Hawaii, at
www.weather.gov/hfo for information specific to the Hawaiian
Islands.


FORECAST POSITIONS AND MAX WINDS

INIT  02/0900Z 16.8N 136.4W   60 KT  70 MPH
 12H  02/1800Z 17.2N 138.7W   60 KT  70 MPH
 24H  03/0600Z 17.9N 141.7W   55 KT  65 MPH
 36H  03/1800Z 18.5N 144.3W   50 KT  60 MPH
 48H  04/0600Z 19.0N 146.6W   45 KT  50 MPH
 72H  05/0600Z 20.3N 151.3W   35 KT  40 MPH
 96H  06/0600Z 23.5N 155.0W   30 KT  35 MPH
120H  07/0600Z 28.0N 156.0W   30 KT  35 MPH

$$
Forecaster Berg

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