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Hurricane FLORENCE


Hurricane Florence Discussion Number  26
NWS National Hurricane Center Miami FL       AL062018
500 PM AST Wed Sep 05 2018

Florence has continued to intensify during the day, with colder
cloud tops completely encircling a clearer eye. Both subjective and
objective Dvorak estimates have unanimously increased to T6.0/115
kt, and on this basis, the initial intensity is raised to 115 kt,
making Florence a category 4 hurricane.

Florence appears to be right along the southern edge of a zone of
stronger vertical shear and continues to defy the intensity
guidance, which has consistently been predicting weakening.  That
said, the last few satellite images indicate that the eye may be
becoming slightly disrupted by the shear.  Since the shear is
anticipated to increase during the next day or so, gradual weakening
is shown in the short-term official forecast, which lies along the
upper end of the guidance through 48 hours.  Beyond 48 hours,
vertical shear is anticipated to weaken, which would allow Florence
to intensify and potentially regain major hurricane status. However,
Florence will need to thread the needle between areas of stronger
shear for this to happen, and there is significant uncertainty in
the intensity forecast.  The new official intensity forecast is
little changed from before except to adjust upward to account for
the higher initial intensity.

The initial motion estimate remains northwestward, or 305/11 kt.
Strong upper-level ridging is forecast to strengthen north of
Florence over the next few days, forcing the hurricane to turn
toward the west-northwest through about 48 hours.  Track guidance is
good agreement during this period, and the official forecast is
essentially an update to the previous one.  Beyond day 2, a break
forms in the ridge, which results in a weakening of the steering
currents, a slowdown in Florence's forward speed, and a turn back
toward the northwest. The new official forecast is shifted south a
bit on days 3-5 to account for recent model trends and is closest to
the TVCN consensus.

It should be noted that there is considerable model ensemble spread
and run-to-run variability for Florence's track beyond day 5. Given
the large uncertainty at these time ranges, it is far too soon to
speculate what, if any, impacts Florence may have on the U.S. East
Coast next week. Regardless of Florence's eventual track, large
swells emanating from the hurricane will reach Bermuda beginning on
Friday, resulting in life-threatening surf and rip currents on the
island. Swells from Florence could also reach the U.S. East Coast by
early next week.


INIT  05/2100Z 22.7N  46.6W  115 KT 130 MPH
 12H  06/0600Z 23.5N  48.1W  110 KT 125 MPH
 24H  06/1800Z 24.5N  49.7W  105 KT 120 MPH
 36H  07/0600Z 25.2N  51.3W  100 KT 115 MPH
 48H  07/1800Z 25.5N  52.9W   95 KT 110 MPH
 72H  08/1800Z 26.0N  55.3W  100 KT 115 MPH
 96H  09/1800Z 27.0N  57.4W  105 KT 120 MPH
120H  10/1800Z 29.0N  60.0W  105 KT 120 MPH

Forecaster Berg/Rhome