[Tropical] Tropical Cyclone Discussion

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WTNT41 KNHC 310836
TCDAT1

HURRICANE FRED DISCUSSION NUMBER   6
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL062015
500 AM AST MON AUG 31 2015

Fred's overall cloud pattern has only changed slightly since the
previous advisory. However, the inner-core convection has increased
markedly, including the development of a well-defined, vertically
deep, 15 n mi diameter eye as noted in recent AMSR and AMSU passive
microwave satellite data. Upper-level outflow is good in all
quadrants. The initial intensity has been increased to 70 kt based
on a blend of satellite intensity estimates of T4.0/65 kt from TAFB,
a UW-CIMSS ADT value of T4.4/75 kt, and a NHC objective Dvorak
T-number of T4.5/77 kt.

Fred has maintained a steady northwestward motion but has slowed
down some, and is now moving 305/10 kt. The track forecast and
rationale remain unchanged from the previous advisory. Water
vapor-derived winds indicate that the break in the subtropical ridge
to the northwest of the Cape Verde Islands is beginning to fill in
based on previous southwesterly winds now having been replaced by
east-northeasterly mid- to upper-level winds. Fred is expected to
continue its northwestward motion for the next 12-24 hours and pass
near or over the Cape Verde Islands of Boa Vista this morning, and
over or near Sao Nicolau, Sao Vicente, and Santo Antao late this
afternoon and into tonight. As the ridge builds steadily westward to
the north of Fred, the hurricane should gradually turn toward the
west-northwest by 36 hours and beyond. This will bring the cyclone
over progressively cooler waters and into increasing vertical wind
shear conditions. The official forecast track is just an update of
the previous advisory track, and lies close to the consensus of the
GFS and ECMWF model tracks.

The vertical shear is expected to remain quite low at less than
5 kt for the next 12 hours as Fred is passing through the Cape Verde
Islands archipelago. With ocean temperatures remaining above 27 deg
C during that time, some additional strengthening is possible. After
the hurricane clears the Cape Verde Islands, however, the
combination of decreasing SSTs, decreasing mid-level moisture, and
increasing west-southwesterly vertical wind shear should induce a
gradual weakening trend. The NHC intensity forecast is similar to
the previous advisory and closely follows the IVCN consensus model
through 36 hours, and is lower than IVCN from 48-120 hours.

Please note that the track/cone graphic, an automatically generated
product, does not have the capability of displaying warnings for the
Cape Verde Islands.

FORECAST POSITIONS AND MAX WINDS

INIT  31/0900Z 15.6N  22.9W   70 KT  80 MPH
 12H  31/1800Z 16.6N  24.3W   75 KT  85 MPH
 24H  01/0600Z 17.9N  26.1W   70 KT  80 MPH
 36H  01/1800Z 19.0N  28.0W   65 KT  75 MPH
 48H  02/0600Z 19.7N  29.8W   55 KT  65 MPH
 72H  03/0600Z 20.8N  33.4W   45 KT  50 MPH
 96H  04/0600Z 22.0N  36.9W   35 KT  40 MPH
120H  05/0600Z 23.0N  40.0W   30 KT  35 MPH

$$
Forecaster Stewart
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