Official Discussion issued by the National Hurricane Center

Florence (AL062018) DATA RELEASED: 9/10/2018 5:00:00 AM UTC

Copy of official data

Hurricane Florence Discussion Number  44
NWS National Hurricane Center Miami FL       AL062018
500 AM AST Mon Sep 10 2018

Florence is rapidly strengthening this morning.  The satellite
presentation has improved markedly overnight with a small 10-n-mi
wide-eye becoming apparent in infrared satellite pictures.  The
upper-level outflow continues to expand over the northern and
northwestern portions of the storm, but is somewhat restricted over
the southeastern quadrant.  Dvorak satellite classifications from
TAFB and SAB supported an intensity of around 80 kt at 0600 UTC, but
with the cooling of the cloud tops around the eye since that time,
the initial intensity has been increased to 90 kt for this advisory.

Satellite fixes indicate that Florence has turned west-northwestward
(285 degrees), and is moving at a slightly faster forward speed of
8 kt.  A high pressure ridge building to the north and northwest of
Florence is expected to steer the hurricane west-northwestward to
northwestward at a much faster forward speed over the southwest
Atlantic during the next few days. After that time, a building
ridge over the Ohio Valley is expected to cause a gradual reduction
in the forward speed of the cyclone as it approaches the
southeastern United States coastline.  The latest run of the ECMWF
has shifted southwestward, along with its ensemble suite, while
there was little overall change in the GFS and its ensemble.  On
the other hand, the UKMET shifted northeastward and is now along
the right side of the guidance envelope.  With these changes to the
guidance, the overall spread has increased this cycle, however, the
corrected consensus aids (FSSE and HCCA) are not much different
than before, and the NHC track again follows these models very
closely.  Users are cautioned to not focus on the exact forecast
track as the average NHC errors at days 4 and 5 are about 140
and 180 n mi, respectively.

Florence will be traversing very warm SSTs of around 29C and
remain within a very favorable upper-level environment during the
next couple of days.  These conditions are expected to lead to
significant strengthening during the next 12 to 24 hours, and
Florence is forecast to be a very powerful major hurricane on
its approach to the southeastern United States.  The NHC intensity
forecast is slightly above all of the intensity guidance during the
first 24 hours, and is then a blend of the FSSE and HCCA models.
The global model guidance also increases the size of Florence's wind
field during the next few days, and this has been reflected in
the NHC wind radii forecast.

The NOAA G-IV jet is conducting another synoptic surveillance
mission this morning in support of the 1200 UTC model cycle, and
these flights will continue through Tuesday. A NOAA P-3 Hurricane
Hunter aircraft is also scheduled to conduct a research mission
into Florence this morning, with Air Force C-130 fix missions
beginning late this afternoon.  Additional upper-air data are
being collected across portions of the central and eastern U.S.
via special 0600 UTC and 1800 UTC radiosonde launches.  Hopefully
these data will help improve the track and intensity forecasts.


Key Messages:

1. There is an increasing risk of life-threatening impacts from
Florence: storm surge at the coast, freshwater flooding from a
prolonged and exceptionally heavy rainfall event inland, and
damaging hurricane-force winds. 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.

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


FORECAST POSITIONS AND MAX WINDS

INIT  10/0900Z 24.9N  58.9W   90 KT 105 MPH
12H  10/1800Z 25.4N  60.5W  110 KT 125 MPH
24H  11/0600Z 26.1N  63.1W  120 KT 140 MPH
36H  11/1800Z 27.3N  66.2W  125 KT 145 MPH
48H  12/0600Z 28.8N  69.3W  130 KT 150 MPH
72H  13/0600Z 32.2N  74.8W  125 KT 145 MPH
96H  14/0600Z 34.5N  78.1W  100 KT 115 MPH
120H  15/0600Z 35.8N  79.6W   40 KT  45 MPH...INLAND

$$
Forecaster Brown