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Hurricane FLORENCE


Hurricane Florence Discussion Number  47
NWS National Hurricane Center Miami FL       AL062018
1100 PM AST Mon Sep 10 2018

The rapid intensification of Florence ended just after the last
advisory, with the central pressure falling to near 939 mb.  Since
that time, the eyewall convection has become a bit ragged and the
latest central pressure from the Air Force Reserve Hurricane Hunter
aircraft is near 944 mb.  The initial intensity will remain a
possibly generous 120 kt for this advisory based on the aircraft
winds.  Microwave imagery suggests that Florence may be starting an
eyewall replacement cycle.  However, the winds from the Hurricane
Hunter did not clearly indicate the presence of an outer eyewall.

Florence should remain in a light shear environment and over sea
surface temperatures near 29C for at least the next 48 h.  Thus,
there is little other than eyewall replacement cycles to keep the
hurricane from intensifying further as indicated by all of the
intensity guidance.  The new intensity forecast calls for continued
strengthening to near category 5 strength, although at a slower rate
than what occurred during the last 30 h.  Florence is expected to
encounter southwesterly shear near the 72 h point, which could
cause slight weakening before landfall.  However, there remains high
confidence that Florence will be a large and extremely dangerous
hurricane, regardless of its exact intensity.

The initial motion is 290/11.  A building mid-level ridge over the
northwestern Atlantic is expected to steer Florence
west-northwestward to northwestward with an increase in forward
speed during the next 48 h.  After that time, a marked decrease in
forward speed is likely as another ridge builds over the Great
Lakes to the north of Florence.  The track guidance continues to
show some spread between the ECMWF on the left side of the envelope
and the GFS on the right side.  Overall, though, the guidance has
again shifted a little to the right, and the 72-96 h points are
nudged just a little to the right from the previous forecast.  It is
important not to focus on the exact forecast track as average NHC
errors at days 3, 4, and 5 are about 100, 140 and 180 n mi,
respectively, and dangerous hazards will extend well away from the

The NOAA G-IV jet will continue to conduct synoptic surveillance
missions every 12 h through at least Wednesday. In addition, special
0600 UTC and 1800 UTC radiosonde launches have been expanded to
additional upper-air stations across the U.S. to collect extra data
for the numerical models.  The next Air Force Reserve Hurricane
Hunter mission into Florence is scheduled for near 12Z.

Key Messages:

1. A life-threatening storm surge is likely along portions of the
coastlines of South Carolina, North Carolina, and Virginia, and
a Storm Surge Watch will likely be issued for some of these areas by
Tuesday morning. All interests from South Carolina into the mid-
Atlantic region should ensure they have their hurricane plan in
place and follow any advice given by local officials.

2. Life-threatening freshwater flooding is likely from a prolonged
and exceptionally heavy rainfall event, which may extend inland over
the Carolinas and Mid Atlantic for hundreds of miles 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 Watch
will likely be issued by Tuesday morning.  Damaging winds could also
spread well inland into portions of the Carolinas and Virginia.

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.


INIT  11/0300Z 25.9N  62.4W  120 KT 140 MPH
 12H  11/1200Z 26.5N  64.5W  125 KT 145 MPH
 24H  12/0000Z 27.9N  67.5W  130 KT 150 MPH
 36H  12/1200Z 29.6N  70.4W  135 KT 155 MPH
 48H  13/0000Z 31.3N  73.2W  130 KT 150 MPH
 72H  14/0000Z 34.0N  76.5W  120 KT 140 MPH
 96H  15/0000Z 35.5N  78.0W   50 KT  60 MPH...INLAND
120H  16/0000Z 36.5N  79.0W   25 KT  30 MPH...INLAND

Forecaster Beven