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Post-Tropical Cyclone Flossie Forecast Discussion

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WTPA42 PHFO 060237

Post-Tropical Cyclone Flossie Discussion Number  35
NWS Central Pacific Hurricane Center Honolulu HI   EP072019
500 PM HST Mon Aug 05 2019

Vigorous deep convection has been persistent through much of the day
to the northeast of the cloud system center, which has become
significantly elongated and poorly defined by several outflow
boundaries. Recent analyses of satellite cloud drift winds suggest
that the highly elongated cloud system center is lacking westerly
winds that define a closed area of low pressure, and subjective
Dvorak current intensity estimates were 25 kt from HFO and SAB,
while JTWC deemed the system too weak to classify. Given these
inputs and the presence of continued vertical wind shear of more
than 30 kt, Flossie will be designated a post-tropical remnant low.
The intensity will remain 30 kt, since an ASCAT-C pass earlier in
the day detected winds this strong within the deep convection. While
the cloud system center could arguably be a trough, a mean center
location gives an initial motion of 300/10 kt.

Under relentless vertical wind shear, the remnant low will continue
to degenerate as it passes near the main Hawaiian Islands. The
westerly vertical wind shear will be maintained by a deep
upper-level trough parked northwest of the Hawaiian Islands. This
upper trough is also eroding the low- to mid-level ridge that is
steering Flossie. As a result, the remnant low will gradually turn
toward the northwest tonight, then shift toward the north-northwest
until dissipation on Wednesday. The track forecast was nudged to the
right from the prior advisory and is near TVCN. All guidance shows
weakening or little change in intensity until dissipation.

This is the last advisory on Flossie. Additional information on this
system can be found in the High Seas Forecasts issued by the
National Weather Service in Honolulu under AWIPS header HFOHSFNP and
WMO header FZPN40 PHFO. Interests in the main Hawaiian Islands
should refer to products issued by the National Weather Service in
Honolulu for information on flooding and surf impacts.


INIT  06/0300Z 20.8N 154.6W   30 KT  35 MPH...POST-TROPICAL
 12H  06/1200Z 22.1N 155.8W   30 KT  35 MPH...POST-TROP/REMNT LOW
 24H  07/0000Z 24.0N 156.8W   30 KT  35 MPH...POST-TROP/REMNT LOW
 36H  07/1200Z 26.0N 157.4W   30 KT  35 MPH...POST-TROP/REMNT LOW
 48H  08/0000Z...DISSIPATED

Forecaster Wroe