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Subtropical Storm Alberto Forecast Discussion


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WTNT41 KNHC 271438
TCDAT1

Subtropical Storm Alberto Discussion Number   9
NWS National Hurricane Center Miami FL       AL012018
1100 AM EDT Sun May 27 2018

The satellite and radar presentation of Alberto has improved
markedly over the past 12 hours or so.  Deep convection has
increased and become organized in a primary band that wraps around
the western and northwestern portions of the storm and the
circulation has also become much better defined than 24 hours ago.
An Air Force Reserve reconnaissance aircraft has recently indicated
that the pressure has fallen to 994 mb.  The aircraft has also
reported peak flight-level winds of 49 kt and believable SFMR winds
of around 40 kt, however, the aircraft has not yet sampled the
northwestern portion of the circulation where the deepest convection
is located.  Assuming that there are slightly higher winds in that
area, the initial intensity has been increased to 45 kt.

With deep convection closer to the center and a slightly smaller
radius of maximum winds, it appears that Alberto is beginning its
transition to a tropical cyclone.  The reconnaissance aircraft data
also indicate that a shallow warm core is present.  It is likely
that Alberto will make the transition to tropical storm later today
or tonight.  As this transition occurs, some additional
strengthening is forecast while Alberto moves over marginally warm
sea surface temperatures and the shear relaxes.  However, dry mid-
level air wrapping around the eastern portion of the circulation
could slow the intensification process before Alberto reaches the
coast.

The initial motion estimate of 005/12 is again highly uncertain due
to the center re-formations that have occurred over the past 12 to
24 hours.  The cyclone should move generally northward today, then
turn northwestward around the northeastern side of a cutoff low over
the central Gulf of Mexico.  The timing and location of landfall of
the center will be dependent on when the northwestward turn occurs.
The latest ECMWF forecast moves Alberto faster northward before it
makes the turn and therefore brings the center onshore much sooner
and farther eastward than the UKMET and GFS.  The NHC forecast is
near the model consensus, and is somewhat faster than the previous
advisory.  Users should remember not to focus on the exact timing
and location of landfall since wind and rain will continue to spread
northward over the northeastern Gulf Coast well ahead of the center.

KEY MESSAGES:

1. Alberto is expected to produce heavy rainfall with a risk of
flooding and flash flooding over western Cuba, the Florida Keys, and
south Florida today.  The risk for heavy rainfall and flooding will
then spread over much of the southeast U.S. tonight and Monday.

2.  Hazardous storm surge is possible along portions of the eastern
Gulf Coast beginning later today, including areas well east of the
track of Alberto's center.  Residents in the storm surge watch area
are encouraged to follow any guidance given by their local
government officials.

3. Tropical storm conditions are likely within the tropical storm
warning area along the Florida west coast today and within the
warning area along the northern Gulf Coast by tonight.

4. Dangerous surf and rip current conditions will continue to
affect portions of the eastern and northern Gulf Coast through
Monday.

FORECAST POSITIONS AND MAX WINDS

INIT  27/1500Z 27.1N  84.4W   45 KT  50 MPH
 12H  28/0000Z 28.7N  84.9W   50 KT  60 MPH...TROPICAL STORM
 24H  28/1200Z 30.3N  85.9W   50 KT  60 MPH...INLAND
 36H  29/0000Z 31.6N  86.4W   35 KT  40 MPH...INLAND
 48H  29/1200Z 33.6N  86.7W   25 KT  30 MPH...INLAND
 72H  30/1200Z 38.3N  87.2W   20 KT  25 MPH...INLAND
 96H  31/1200Z 43.3N  84.7W   15 KT  15 MPH...POST-TROP/REMNT LOW
120H  01/1200Z 46.5N  79.5W   15 KT  15 MPH...POST-TROP/REMNT LOW

$$
Forecaster Brown