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TROPICAL STORM FRED DISCUSSION NUMBER 10
NWS NATIONAL HURRICANE CENTER MIAMI FL AL062015
500 AM AST TUE SEP 01 2015
After a brief convective hiatus between about 0000-0200 UTC, deep
convection has redeveloped over the center of Fred and also in the
northern semicircle. Several passive microwave satellite images
indicate that Fred's low-level center is a little south of the
previous advisory track, due to southerly vertical wind shear
displacing most of the convection to the north of the center.
However, that same imagery also indicated that Fred still has a
low-level circulation that is quite robust, including a nearly
closed 20 n mi diameter eye. The initial intensity of 55 kt is based
on a blend of Dvorak satellite intensity estimates of T4.0/65 kt
from TAFB and T3.0/45 kt from SAB.
The initial motion estimate is 300/10 kt based on microwave fixes.
Fred is expected to move between west-northwest and northwest for
the next 72 hours as a mid-level ridge to the north of the cyclone
gradually builds westward. After that time, a turn toward the
north-northwest and north is forecast due to a deep-layer trough
currently over eastern Canada that is expected to dig southeastward
over the central Atlantic and erode the ridge. The NHC model
guidance is in decent agreement on this developing pattern change.
However, there are significant differences in the model solutions
with the HWRF, GFS, and GFDL models keeping Fred stronger and
making the northward turn sooner, whereas the weaker solution
models like the UKMET and ECMWF take a weaker and more vertically
shallow cyclone farther west before turning it northward.
The official forecast track is a little south of the previous
advisory track, mainly due to the more southerly initial position,
and follows a blend of the weaker UKMET and ECMWF solutions.
Fred is expected to gradually weaken throughout the forecast
period as the cyclone moves into an environment of increasing
southwesterly vertical wind in excess of 20 kt and drier and
more stable air, and over SSTs of near 26 deg C. The NHC intensity
forecast is a little lower than the previous advisory, as well as
the consensus model IVCN.
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 01/0900Z 18.0N 26.1W 55 KT 65 MPH
12H 01/1800Z 18.8N 27.4W 45 KT 50 MPH
24H 02/0600Z 19.7N 29.2W 40 KT 45 MPH
36H 02/1800Z 20.3N 30.7W 35 KT 40 MPH
48H 03/0600Z 21.0N 32.3W 35 KT 40 MPH
72H 04/0600Z 22.3N 35.5W 30 KT 35 MPH
96H 05/0600Z 23.7N 38.6W 25 KT 30 MPH
120H 06/0600Z 26.0N 40.7W 25 KT 30 MPH...POST-TROP/REMNT LOW