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Hurricane Florence Discussion Number 45
NWS National Hurricane Center Miami FL AL062018
1100 AM AST Mon Sep 10 2018

Florence is quickly becoming a powerful hurricane. Satellite images
show that the distinct eye has warmed in the center, with convection
increasing in the eyewall during the past several hours. The initial
wind speed is set to 100 kt, closest to the CIMSS-ADT value. A NOAA
Hurricane Hunter will be in the area later this morning for a more
accurate estimate.

The hurricane is moving over progressively warmer waters over
the next couple of days, with water temperatures peaking near 85F.
In combination with the low vertical wind shear in the forecast
during that time, Florence should continue to strengthen, and all
models show it becoming a category 4 hurricane by tomorrow. The
corrected-consensus guidance has done quite well with this
intensification episode, and I don’t see any reason to deviate much
from them at this time. As Florence approaches the southeastern
United States, there will likely be fluctuations in intensity from
eyewall cycles, but even if this occurs, the hurricane’s wind field
is expected to grow with time, increasing the storm surge and inland
wind threats. The bottom line is that there is increasing
confidence that Florence will be a large and extremely dangerous
hurricane, regardless of its exact intensity.

During the last several hours, Florence has turned westward again,
estimated at 11 kt. The steering currents are becoming well-
defined as as a very strong ridge builds over the northwestern
Atlantic Ocean, forcing Florence to move faster toward the
west-northwest during the next couple of days. By late Wednesday,
a turn toward the northwest is possible due to the orientation of
the Atlantic ridge, along with a slight decrease in forward speed
due to a new ridge building over the Great Lakes. The various
models are shifting around at long range, but the model consensus
has barely budged in the past few model cycles. Thus the new NHC
forecast is close to the previous one, near the NOAA and FSSE
consensus guidance. It is important not to focus on the exact
forecast track as average NHC errors at days 4 and 5 are about 140
and 180 n mi, respectively, and dangerous hazards will extend well
away from the center.

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.

FORECAST POSITIONS AND MAX WINDS

INIT 10/1500Z 25.0N 60.0W 100 KT 115 MPH
12H 11/0000Z 25.5N 61.9W 115 KT 130 MPH
24H 11/1200Z 26.4N 64.7W 125 KT 145 MPH
36H 12/0000Z 27.8N 67.9W 130 KT 150 MPH
48H 12/1200Z 29.5N 71.0W 130 KT 150 MPH
72H 13/1200Z 33.0N 76.3W 125 KT 145 MPH
96H 14/1200Z 35.0N 79.0W 75 KT 85 MPH...INLAND
120H 15/1200Z 36.0N 80.0W 30 KT 35 MPH...INLAND