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Hurricane FLORENCE


Hurricane Florence Discussion Number  41
NWS National Hurricane Center Miami FL       AL062018
1100 AM AST Sun Sep 09 2018

Satellite images indicate that Florence is strengthening.  Deep
convection has intensified in the central dense overcast, with
hints of a ragged eye in the latest GOES-16 visible channel.  The
NOAA Hurricane Hunters just flew through the eye, finding 70 kt
winds at flight-level and 66 kt from the SFMR.  This data confirms
that Florence has become a hurricane again, and the initial wind
speed is set to 65 kt.  The aircraft also found that the minimum
pressure has decreased to 984 mb.

Overnight microwave data and the Hurricane Hunter vortex message
show that a mostly complete eyewall has formed with Florence.  In
combination with low vertical wind shear and progressively warmer
waters near 29C, this structure is a blueprint for rapid
intensification. Almost all of the intensity guidance is showing at
least one period of rapid strengthening during the next few days,
which is rather rare.  The NHC wind speed forecast is raised in the
first couple of days following the guidance trend, then is very
similar to the previous one.  All indications are that Florence will
be an extremely dangerous Category 4 hurricane while it moves over
the western Atlantic toward the southeastern United States.

Florence continues moving slowly westward, caught between a pair
of mid-level ridges over the Atlantic Ocean.  A very strong ridge is
forecast to build over the northwestern Atlantic during the next few
days, which should steer Florence west-northwestward at a much
faster forward speed.  By Wednesday, the hurricane should turn
northwestward, and slow down somewhat due to another ridge forming
over the Ohio Valley.  It is interesting to note that while the
ensemble means from the ECMWF and UKMET are west of the NHC
forecast, the strongest members are on the right side of their
ensemble envelope.  Thus, the new NHC track forecast is very similar
to the previous one, and continues to lie between the corrected
consensus and consensus aids.  The Ohio Valley ridge is concerning
because Florence could stop moving pretty quickly around day 5,
potentially leading to a serious heavy rain episode and inland flood

Key Messages:

1. There is an increasing risk of two life-threatening impacts from
Florence: storm surge at the coast and freshwater flooding from a
prolonged heavy rainfall event inland. While it is too soon to
determine the exact timing, location, and magnitude of these
impacts, interests at the coast and inland from South Carolina into
the mid-Atlantic region should closely monitor the progress of
Florence, ensure they have their hurricane plan in place, and follow
any advice given by local officials.


INIT  09/1500Z 24.4N  56.3W   65 KT  75 MPH
 12H  10/0000Z 24.5N  57.4W   80 KT  90 MPH
 24H  10/1200Z 24.9N  59.3W   95 KT 110 MPH
 36H  11/0000Z 25.6N  61.7W  105 KT 120 MPH
 48H  11/1200Z 26.4N  64.5W  120 KT 140 MPH
 72H  12/1200Z 29.0N  70.8W  125 KT 145 MPH
 96H  13/1200Z 32.2N  75.8W  120 KT 140 MPH
120H  14/1200Z 35.0N  78.5W   85 KT 100 MPH...INLAND

Forecaster Blake