Tropical Storm Florence Discussion Number  39
NWS National Hurricane Center Miami FL       AL062018
1100 PM AST Sat Sep 08 2018

Satellite images indicate that the cloud pattern has continued to
gradually become better organized with an eye feature trying to
form. An average of all of the Dvorak satellite intensity estimates
tonight suggest that Florence is not a hurricane yet, but is close
to being one. The initial intensity is kept at 60 kt in this
advisory.  The recent ASCAT data showed less winds than previously
observed by the NOAA plane when the cloud pattern was less
organized.

There is a band of convection trying to wrap around a possible eye
feature, and that is an indication that Florence has continued to
recover from the hostile shear environment, which brought the
hurricane from Category 4 to a tropical storm in a matter of a day
or so.  The presence of developing upper-level outflow is a
good indication that the shear has decreased, and with the presence
of a warm ocean ahead, strengthening is anticipated.  As indicated
by my predecessor, the official forecast continues to call for a
period of rapid intensification in about 12-24 hours, and Florence
is expected to reach major hurricane intensity between 36-48 hours
with additional strengthening thereafter.  Florence is forecast to
be an intense hurricane on days 3 through 5 as it moves across the
warm waters of the southwestern Atlantic Ocean between the Bahamas
and Bermuda, and then as it heads toward the southeast United States
coast.

Florence is still trapped within very light steering currents,
and is slowly moving toward the west or 270 degrees at 5 kt.
All indications are that this is about to change, as a strong ridge
of high pressure builds to the north of the hurricane. This
forecast flow pattern predicted by the global models will force
Florence on a general west-northwest to northwest track with an
increase in forward speed.  The NHC forecast is basically on top of
the previous one, and is in the middle of the narrow guidance
envelope mainly for the next 3 to 4 days.  By the end of the
forecast period, when the hurricane is approaching the U.S. coast,
the guidance envelope is wider and becomes bounded by the
northernmost GFS and the southernmost HCCA and the FSSE ensembles.
One thing all models coincide at the longer range is with the
collapsing of the steering currents, resulting in a significant
reduction of the forward speed of the hurricane.

Key Messages:

1. Florence is forecast to be a dangerous major hurricane near the
southeast U.S. coast by late next week, and the risk of direct
impacts continues to increase. However, given the uncertainty in
track and intensity forecasts at those time ranges, it's too soon to
determine the exact timing, location, and magnitude of those
impacts.

2. Interests along the U.S. East Coast, particularly from north
Florida through North Carolina, should closely monitor the progress
of Florence, ensure they have their hurricane plan in place, and
follow any advice given by local officials.

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


FORECAST POSITIONS AND MAX WINDS

INIT  09/0300Z 24.6N  55.2W   60 KT  70 MPH
12H  09/1200Z 24.5N  55.9W   70 KT  80 MPH
24H  10/0000Z 24.8N  57.4W   80 KT  90 MPH
36H  10/1200Z 25.2N  59.3W  100 KT 115 MPH
48H  11/0000Z 25.8N  61.8W  110 KT 125 MPH
72H  12/0000Z 27.5N  67.5W  125 KT 145 MPH
96H  13/0000Z 30.0N  73.5W  125 KT 145 MPH
120H  14/0000Z 33.8N  77.8W  115 KT 130 MPH

$$
Forecaster Avila