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Tropical Storm Florence Discussion Number  20
NWS National Hurricane Center Miami FL       AL062018
500 AM AST Tue Sep 04 2018

Florence's cloud pattern has changed very little during the past
several hours, with the exception of a possible small Central Dense
Overcast developing just to the east of the center.  An earlier
AMSR2 overpass revealed a rather obvious tilt toward the
east-northeast, indicative of the moderate southwesterly shear.
The initial intensity is held a 60 kt, and is supported by the
Dvorak subjective and objective T-numbers.

Florence should exhibit little change in strength during the next
24 hours or so, as the cyclone traverses marginally warm sea surface
temperatures and is influenced by modest west-southwesterly shear.
Slight weakening is expected during the mid- forecast period as the
shear gradually increases with time.  Afterward, the upper-level
wind environment should become a little more favorable and, at the
same time, Florence will be moving back over warmer SSTs.
Consequently, the cyclone should gradually strengthen through day 5.
This forecast is unchanged from the previous one, and is in good
agreement with the NOAA-HCCA guidance.

The initial motion estimate is west-northwestward, or 290/11 kt.
The cyclone is expected to be steered west-northwestward for the
next 48 hours by a mid- to upper tropospheric ridge anchored to
the north, followed by a northwestward turn around the 72 hr period
as it enters a growing weakness in the aforementioned ridge.  A
rather large spread in the global and hurricane models remains
particularly beyond day 4, however, the consensus models and the
global ensemble means have have been fairly consistent from run to
run.  This forecast is just a bit to the north of the previous
advisory and just south of the consensus models.

FORECAST POSITIONS AND MAX WINDS

INIT  04/0900Z 19.3N  42.0W   60 KT  70 MPH
 12H  04/1800Z 19.9N  43.7W   60 KT  70 MPH
 24H  05/0600Z 20.8N  45.8W   60 KT  70 MPH
 36H  05/1800Z 21.8N  48.0W   55 KT  65 MPH
 48H  06/0600Z 22.9N  50.2W   50 KT  60 MPH
 72H  07/0600Z 25.2N  53.4W   50 KT  60 MPH
 96H  08/0600Z 27.1N  55.6W   55 KT  65 MPH
120H  09/0600Z 29.1N  57.7W   65 KT  75 MPH

$$
Forecaster Roberts

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