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TROPICAL STORM FIONA DISCUSSION NUMBER 14
NWS NATIONAL HURRICANE CENTER MIAMI FL AL062016
500 AM AST SAT AUG 20 2016
Fiona is looking ragged this morning with only a small area of deep
convection on the northern side of the apparent center of the
cyclone. Dvorak estimates are a bit lower than earlier, but I've
elected to keep Fiona a tropical storm for this advisory given the
earlier ASCAT data, perhaps generously. The cyclone is likely to
gradually weaken for the next few days with strong shear, upper-
level convergence, and dry mid-level air in its path. After
considering the unfavorable environment ahead, the NHC intensity
forecast is reduced from the previous one, and now shows Fiona as a
remnant low in 48 hours and dissipating by day 5. This forecast
could be conservative since the ECMWF and UKMET now open up this
system into a trough within 3 days.
The initial motion estimate is about the same as before, 295/11,
mostly based on extrapolation. A subtropical ridge over the
central Atlantic should keep Fiona moving west-northwestward for
the next few days. The long-range track forecast remains highly
contingent on Fiona's status as a tropical cyclone, a remnant low,
or a trough. A deeper cyclone would likely take a more northern
turn at the end of the period due to a mid-level trough, while a
weaker cyclone would probably just continue moving to the
west-northwest (and not feel the trough). Since the cyclone is now
expected to be a more shallow system in a few days, it makes sense
to be on the western side of the guidance envelope, which requires
the new NHC track forecast to be shifted leftward beyond day 2.
FORECAST POSITIONS AND MAX WINDS
INIT 20/0900Z 19.2N 46.7W 35 KT 40 MPH
12H 20/1800Z 20.0N 48.4W 30 KT 35 MPH
24H 21/0600Z 21.1N 50.8W 30 KT 35 MPH
36H 21/1800Z 22.1N 53.4W 30 KT 35 MPH
48H 22/0600Z 23.1N 56.0W 25 KT 30 MPH...POST-TROP/REMNT LOW
72H 23/0600Z 25.0N 61.0W 25 KT 30 MPH...POST-TROP/REMNT LOW
96H 24/0600Z 27.0N 63.5W 20 KT 25 MPH...POST-TROP/REMNT LOW
120H 25/0600Z...DISSIPATED
$$
Forecaster Blake
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