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Tropical Storm Florence Discussion Number  34
NWS National Hurricane Center Miami FL       AL062018
500 PM AST Fri Sep 07 2018

Little has changed with Florence's structure during the day.  The
low-level center is located on the southwestern side of the deep
convection due to moderate to strong southwesterly shear, and
satellite intensity estimates are essentially the same from this
morning.  Therefore, the estimated maximum winds remain 55 kt.
NOAA is scheduled to conduct a research mission with the P-3
aircraft tomorrow, which should provide some useful wind data and
give us a better handle on the cyclone's intensity.

Vertical shear is still expected to gradually decrease over the
next day or two, likely reaching values of 10 kt or less by 48
hours.  During this period, Florence should become more vertically
stacked, which would allow for some reintensification, possibly back
to hurricane strength within 36-48 hours.  After 48 hours, the shear
is expected to remain generally low, and oceanic heat content values
will increase significantly as Florence moves over the waters
between Bermuda and the northern Leeward Islands.  This is a
classic recipe for a quick intensification trend, and Florence is
expected to become a major hurricane by days 4 and 5.  The
generally skillful HCCA, Florida State Superensemble, and ICON
intensity consensus are all near 110-115 kt by day 5, and because
of this, no notable changes were required from the previous
official intensity forecast.

Florence has been moving south of due west (260 degrees) at 7 kt,
located south of a low- to mid-level ridge.  The cyclone is
expected to continue moving generally westward for the next 48
hours while it remains sheared.  As Florence begins to strengthen
and become vertically stacked after 48 hours, it should begin to
turn west-northwestward, steered by a deeper flow regime.  By days
4 and 5, an exceptionally strong blocking ridge is forecast to
develop between Bermuda and the Northeast U.S., keeping Florence
on a west-northwestward trajectory with an increase in forward
speed by the end of the forecast period.  A slight southwestward
adjustment was made to the NHC forecast to account for Florence's
initial motion and a slight shift in the overall guidance envelope.
For most of the forecast period, the official forecast is close to
a blend of the GFS and ECMWF.

Key Messages:

1. Regardless of Florence's eventual track, large swells are
affecting Bermuda and will begin to affect portions of the U.S. East
Coast this weekend, resulting in life-threatening surf and rip
currents.

2. The risk of other direct impacts associated with Florence along
the U.S. East Coast next week has increased.  However, there is
still very large uncertainty in model forecasts of Florence's track
beyond day 5, making it too soon to determine the exact location,
magnitude, and timing of these impacts.  Interests near and along
the U.S. East Coast should monitor the progress of Florence through
the weekend and ensure they have their hurricane plans in place.

FORECAST POSITIONS AND MAX WINDS

INIT  07/2100Z 24.8N  52.5W   55 KT  65 MPH
 12H  08/0600Z 24.6N  53.5W   55 KT  65 MPH
 24H  08/1800Z 24.6N  54.7W   55 KT  65 MPH
 36H  09/0600Z 24.6N  55.8W   60 KT  70 MPH
 48H  09/1800Z 24.8N  57.0W   70 KT  80 MPH
 72H  10/1800Z 25.8N  60.9W   90 KT 105 MPH
 96H  11/1800Z 27.5N  67.0W  110 KT 125 MPH
120H  12/1800Z 30.5N  73.0W  115 KT 130 MPH

$$
Forecaster Berg

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