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Tropical Storm Florence Discussion Number  13
NWS National Hurricane Center Miami FL       AL062018
1100 AM AST Sun Sep 02 2018

Florence's convective cloud appearance has become rather disheveled
this morning, with most of the deep convection sheared to the east
and northeast of the now fully exposed but well-defined low-level
circulation center. Both subjective and objective satellite
intensity estimates have decreased, especially the objective ADT
estimates from UW-CIMSS. Based on a blend of the available
estimates, the intensity has been lowered to 45 kt.

The initial motion is 285/16. Now that the system has weakened and
become more vertically shallow, a more westward component of motion
is expected throughout the forecast period. All but the GFS and HWRF
models have picked up on this more westerly component of motion, and
the ECMWF and UKMET models are now the southernmost models in the
guidance suite. Since the ridge to the north is expected to remain
intact and even build more westward over the next 5 days, the new
NHC track forecast has been shifted southward and to the left of the
previous advisory track, and lies close to a blend of the HCCA,
FSSE, and TCVN track consensus models.

Analyses from UW-CIMSS indicate that westerly to southwesterly
vertical wind shear of 15-20 kt is undercutting the otherwise
favorable upper-level outflow pattern noted in water vapor imagery
and by the GFS- and ECMWF-based SHIPS model, which show the shear
to be less than 10 kt. GOES-16 mid-level water vapor imagery also
reveals that Florence is ingesting considerable dry air in the
western and southern quadrants, with the dry mid-level air having
penetrated into the inner-core region. Since the vertical shear is
expected to get a little worse over the next 3-4 days while the
cyclone is moving over SSTs near 26 deg C, little change in strength
is forecast through 96 h. By 120 h, however, Florence is forecast to
move over warmer waters with SSTs exceeding 28 deg C and also into
a weaker shear environment, which should allow for some
re-strengthening to occur. The new NHC intensity forecast is a
little lower than the one in the previous advisory, and closely
follows the consensus model IVCN, through 96 h, and then is a
little above the guidance at 120 h.

FORECAST POSITIONS AND MAX WINDS

INIT  02/1500Z 17.0N  33.2W   45 KT  50 MPH
 12H  03/0000Z 17.4N  35.3W   45 KT  50 MPH
 24H  03/1200Z 17.9N  38.2W   45 KT  50 MPH
 36H  04/0000Z 18.4N  40.7W   45 KT  50 MPH
 48H  04/1200Z 18.9N  42.8W   45 KT  50 MPH
 72H  05/1200Z 20.5N  47.0W   45 KT  50 MPH
 96H  06/1200Z 22.4N  51.0W   45 KT  50 MPH
120H  07/1200Z 24.3N  54.3W   55 KT  65 MPH

$$
Forecaster Stewart

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