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Tropical Depression Fred Discussion Number  17
NWS National Hurricane Center Miami FL       AL062021
500 PM EDT Fri Aug 13 2021
 
Although there has been a general increase in convection
associated with Fred since this morning, the system remains
disorganized with the low-level center moving farther inland over
central Cuba. Earlier ASCAT data detected an area of 25-27 kt
winds over water to the northeast of the center, and based on that
data, the initial intensity is held at 30 kt, which could be a
little generous.
 
Since the previous advisory, Fred has been moving nearly due 
westward, but the longer-term motion is estimated to be 280/10 kt. 
The cyclone is nearing the western periphery of a subtropical ridge 
that is centered over the western Atlantic. This should cause Fred 
to turn west-northwestward tonight, and then northwestward 
on Saturday. The latest interpolated guidance that was 
initialized with the more southward and westward 18Z initial 
position shows a wider or more gradual northwestward turn, and 
therefore has shifted significantly westward, especially in the 
short term.  However, the global models fields track the 850-mb 
vorticity center more along the northern coast of Cuba and some of 
those models suggest a center re-formation could occur on Saturday 
near the north coast of Cuba or over the Straits of Florida. As a 
result, the first 24-36 hours of the track forecast has been 
adjusted about a degree westward, but it is not as far west as the 
trackers, leaving open the possibility that a center re-formation 
could occur. After that time, the NHC forecast lies along the 
eastern side of the guidance envelope in best agreement with the 12Z 
GFS.  Some additional westward adjustments may be necessary until 
the track guidance stabilizes. It is worth noting that it isn't too 
surprising to see these type of models shifts with a system that 
remains quite disorganized.
 
Fred remains within an area of moderate southwesterly vertical wind 
shear, and the model guidance generally indicates that this shear 
will continue during the next day or so. Since it will also take 
time for the system to recover after its passage over Cuba, only 
gradual strengthening is indicated during the next day or two. After 
that time, the system could be in a somewhat more favorable 
environment, and the NHC intensity forecast calls for some 
strengthening until Fred reaches the northern Gulf Coast, which now 
doesn't occur until around 72 hours with the wider turn shown in 
the track forecast. The NHC intensity forecast lies between the 
various consensus aids, the statistical guidance, and the HWRF 
model, which all generally show the system peaking in 60-72 hours. 
The intensity forecast remains of lower-than-normal confidence due 
to Fred's continued interaction with land.
 
Users are reminded to not focus on the exact forecast track as
heavy rainfall, gusty winds, and a chance of tornadoes will extend
far to northeast and east of the center, and those hazards are
likely to still affect portions of the Florida peninsula, despite
the recent shift in the forecast track.
 
KEY MESSAGES:
 
1. Today through Monday, heavy rainfall could lead to areal, urban,
small stream, and exacerbated river flooding across southern and
central Florida into the Big Bend.  From Sunday onward, heavy rain
and flood impacts could extend into other portions of the Southeast
and into the southern and central Appalachians and Piedmont as Fred
interacts with a front in that area.
 
2. Tropical storm conditions are expected in portions of the
Florida Keys on Saturday, where a Tropical Storm Warning is in
effect.
 
3. Tropical storm conditions are possible late Saturday and
early Sunday across portions of the west coast of Florida in the
Tropical Storm Watch area. The risk of tropical storm conditions
will spread northward along the Florida west coast and to the
Florida Panhandle Sunday and Monday.
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  13/2100Z 22.3N  79.6W   30 KT  35 MPH...INLAND
 12H  14/0600Z 23.0N  81.0W   30 KT  35 MPH...INLAND
 24H  14/1800Z 24.2N  82.6W   35 KT  40 MPH...OVER WATER
 36H  15/0600Z 25.4N  83.7W   35 KT  40 MPH
 48H  15/1800Z 27.0N  84.8W   40 KT  45 MPH
 60H  16/0600Z 28.8N  85.7W   45 KT  50 MPH
 72H  16/1800Z 30.2N  86.2W   50 KT  60 MPH
 96H  17/1800Z 33.5N  86.5W   25 KT  30 MPH...INLAND
120H  18/1800Z 37.0N  85.0W   20 KT  25 MPH...POST-TROP/INLAND
 
$$
Forecaster Brown
 
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