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Hurricane FLORENCE


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Hurricane Florence Discussion Number  52
NWS National Hurricane Center Miami FL       AL062018
500 AM EDT Wed Sep 12 2018

The eye of Florence remains very distinct in infrared satellite
imagery this morning.  There has been little change to the cloud top
temperatures surrounding the eye overnight, however, the overall
cloud shield and central dense overcast has become slightly more
symmetric.  An Air Force Reserve Hurricane Hunter aircraft that was
in the hurricane until just after midnight measured a peak 700-mb
flight-level wind of 130 kt, and a SFMR wind of 107 kt in the
northeast eyewall.  A blend of these data and recent subjective and
objective satellite intensity estimates supports an initial wind
speed of 115 kt.  Florence will be moving over sea surface
temperatures of around 29C and through an area of low vertical wind
shear during the next day or so.  These conditions favor some
strengthening, but eyewall replacement cycles could cause some
fluctuations in intensity during that time. After that time, an
increase in southwesterly shear, upwelling, and interaction with
land is likely to lead to some weakening, however, Florence is
expected to remain a dangerous major hurricane as it approaches the
coastline.  The new NHC intensity forecast is near the higher
statistical guidance through 48 hours, then follows the trend of
the decay SHIPS model after that time.

Florence is moving west-northwestward or 300 degrees at 15 kt.
There has been no change to the track forecast or reasoning for the
first 36-48 hours, as Florence will continue to be steered
west-northwestward to northwestward around the southwestern portion
of a mid-level ridge centered northeast of Bermuda.  By late
Thursday, a mid-level ridge is forecast to begin building over the
east-central United States, which is expected to cause Florence
to slow down significantly by 48 hours.  The track guidance is in
good agreement through the first couple of days of the forecast
period, and the NHC track forecast again brings the center of the
hurricane very close to the coasts of North and South Carolina
within 48 hours.  Later in the period, the dynamical model spread
increases but most of the guidance has continued its southward
shift, and now take Florence southwestward near the coast of South
Carolina by day 4.  The NHC track has been adjusted southward at
days 4 and 5, and is a little north of the consensus out of respect
for continuity, however, the GFS, ECMWF, and the ECMWF ensemble mean
is south of the NHC track forecast, and additional southward
adjustment may be warranted in future advisories.

It is important for users to realize that significant impacts extend
well away from the center of Florence, and serious hazards such as
a dangerous storm surge and flooding rains will cover a large area
regardless of exactly where the center moves.

Key Messages:

1. A life-threatening storm surge is now highly likely along
portions of the coastlines of South Carolina and North Carolina, and
a Storm Surge Warning is in effect for a portion of this area.  All
interests from South Carolina into the mid-Atlantic region should
complete preparations and follow any advice given by local
officials.

2. Life-threatening, catastrophic flash flooding and significant
river flooding is likely over portions of the Carolinas and
Mid-Atlantic states from late this week into early next week, as
Florence is expected to slow down as it approaches the coast and
moves inland.

3. Damaging hurricane-force winds are likely along portions of the
coasts of South Carolina and North Carolina, and a Hurricane Warning
is in effect.  Strong winds could also spread inland into portions
of the Carolinas.

4. Large swells affecting Bermuda and portions of the U.S. East
Coast will continue this week, resulting in life-threatening surf
and rip currents.


FORECAST POSITIONS AND MAX WINDS

INIT  12/0900Z 29.0N  70.1W  115 KT 130 MPH
 12H  12/1800Z 30.3N  72.1W  120 KT 140 MPH
 24H  13/0600Z 32.0N  74.4W  125 KT 145 MPH
 36H  13/1800Z 33.2N  76.1W  120 KT 140 MPH
 48H  14/0600Z 33.8N  77.3W  105 KT 120 MPH...NEAR THE COAST
 72H  15/0600Z 33.8N  78.2W   85 KT 100 MPH...NEAR THE COAST
 96H  16/0600Z 33.6N  79.7W   45 KT  50 MPH...INLAND
120H  17/0600Z 34.2N  82.7W   25 KT  30 MPH...INLAND

$$
Forecaster Brown

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