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Tropical Storm FRED Forecast Discussion


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000
WTNT41 KNHC 020836
TCDAT1

TROPICAL STORM FRED DISCUSSION NUMBER  14
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL062015
500 AM AST WED SEP 02 2015

Fred has been devoid of significant deep convection near the
center for almost 6 hours. The pronounced upper-level circulation
and associated convection is displaced at least 150 n mi to the
east of the now fully exposed low-level circulation due to strong
westerly vertical wind shear. The initial intensity of 40 kt is
based on a gradual spin down of the 45-kt ASCAT-B vortex mentioned
in the previous discussion, and a blend of 35-kt and 45-kt Dvorak
satellite intensity estimates from SAB and TAFB, respectively.

Now that the upper-level circulation has decoupled from the low- and
mid-level circulations, it is unlikely that Fred will restrengthen
since the cyclone will be moving over cooler SSTs of about 26 deg C,
into even stronger shear in excess of 30 kt, and also into a much
drier airmass. Cloud top temperatures in the radius of maximum
winds are only in the -10 to -20 deg C range, which suggests that
Fred's circulation now likely only extends no higher than the 400-mb
level, if that. As a result, Fred should continue to slowly spin
down and become a depression within the next 18-24 hours, and
degenerate into a remnant low within 36 hours, if not sooner. The
NHC intensity forecast follows a blend of the SHIPS, LGEM, and HWRF
models, which steadily weaken Fred, and is lower than the IVCN model
due to the GFDL model re-strengthening Fred into a 75-kt hurricane
again, which has created a high bias in the consensus.

The initial motion estimate is 295/09.  There remains no significant
change to the previous track forecast or reasoning. Fred is
expected to continue moving west-northwestward for the next 72 hours
or so while it remains embedded within the trade wind flow south of
the Bermuda-Azores subtropical high. After that time, the models
continue to forecast a mid-latitude trough to dig southward over
the central Atlantic and erode the western portion of the ridge,
allowing Fred to turn slowly northwestward by 96 hours and
northward by 120 hours. The new forecast track is a tad south of
the previous advisory track, mainly due to the more southerly
initial position. The track forecast also lies along the southern
edge of the guidance envelope and is left of the TVCA consensus
model due to the more northerly track created by the much stronger
and vertically deeper GFDL model, which has strongly biased the
consensus model with a more northward and eastward track.

FORECAST POSITIONS AND MAX WINDS

INIT  02/0900Z 19.5N  30.1W   40 KT  45 MPH
 12H  02/1800Z 20.0N  31.4W   35 KT  40 MPH
 24H  03/0600Z 20.7N  32.9W   30 KT  35 MPH
 36H  03/1800Z 21.2N  34.5W   25 KT  30 MPH...POST-TROP/REMNT LOW
 48H  04/0600Z 21.6N  35.9W   25 KT  30 MPH...POST-TROP/REMNT LOW
 72H  05/0600Z 22.3N  39.0W   20 KT  25 MPH...POST-TROP/REMNT LOW
 96H  06/0600Z 23.5N  41.7W   20 KT  25 MPH...POST-TROP/REMNT LOW
120H  07/0600Z 25.6N  43.3W   20 KT  25 MPH...POST-TROP/REMNT LOW

$$
Forecaster Stewart



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Page last modified: Wednesday, 02-Sep-2015 08:36:46 UTC