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Tropical Storm FRANK Forecast Discussion


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000
WTPZ42 KNHC 240836
TCDEP2

TROPICAL STORM FRANK DISCUSSION NUMBER  11
NWS NATIONAL HURRICANE CENTER MIAMI FL       EP072016
300 AM MDT SUN JUL 24 2016

Frank's cloud pattern has not changed appreciably in organization
since the last advisory.  The cloud pattern remains characterized by
a ball of deep convection with some evidence of outer banding.  An
0408 UTC Ascat-B overpass suggested winds of around 55 kt, at best.
The initial intensity estimate is therefore held at this value.

The initial motion estimate is 305/07.  A weak mid- to upper-level
perturbation near the Baja California peninsula could be responsible
for Frank's more northwesterly motion today, which is forecast to
persist for a little longer.  Once this feature dissipates in a day
or so, Frank should be steered west-northwestward or westward at a
relatively slow forward speed to the south of a subtropical ridge
centered over the southwestern United States.  The track guidance is
in generally good agreement on this scenario, though there are some
speed differences between the various solutions.  The NHC forecast
track represents a blend of the ECMWF and GFS solutions and is
slightly north of the previous forecast after 24 hours.

The cyclone has already moved out of the warmest waters of the
basin and is forecast to reach sub-26 deg C in about 60 hours.
This would seem to still give Frank an opportunity to strengthen
some, but northeasterly to easterly vertical shear over the storm is
not forecast to abate.  The NHC intensity forecast thus keeps Frank
at the same strength for a day or so and then shows slow weakening.
Further weakening should occur by day 3 when Frank reaches
significantly cooler waters and becomes embedded in a drier and more
stable air mass.  The guidance suggests that Frank should become a
remnant low in about 4 days, and so does the official forecast.  The
new forecast is close to a blend of the statistical-dynamical
models.

FORECAST POSITIONS AND MAX WINDS

INIT  24/0900Z 19.9N 111.8W   55 KT  65 MPH
 12H  24/1800Z 20.2N 112.7W   55 KT  65 MPH
 24H  25/0600Z 20.7N 113.8W   55 KT  65 MPH
 36H  25/1800Z 21.0N 114.9W   50 KT  60 MPH
 48H  26/0600Z 21.1N 116.2W   45 KT  50 MPH
 72H  27/0600Z 21.9N 119.1W   35 KT  40 MPH
 96H  28/0600Z 22.9N 122.1W   30 KT  35 MPH...POST-TROP/REMNT LOW
120H  29/0600Z 23.1N 124.5W   20 KT  25 MPH...POST-TROP/REMNT LOW

$$
Forecaster Kimberlain