[Tropical] Tropical Cyclone Discussion

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WTNT41 KNHC 190846
TCDAT1

TROPICAL STORM FIONA DISCUSSION NUMBER  10
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL062016
500 AM AST FRI AUG 19 2016

Fiona hasn't really changed much overall in the past several hours
with an earlier burst of convection having dissipated and a new
burst taking its place.  Microwave data suggest the center is near
or south of the main area of thunderstorms, which is a sign of
the ongoing southwesterly shear.  The initial wind speed is kept at
40 kt for this advisory since the Dvorak estimates are the same as
the previous cycle.  Little significant change is expected with
Fiona's intensity today due to gradually increasing shear.  The
storm should weaken over the weekend as the shear further increases,
along with the likely entrainment of drier mid-level air.  While the
environmental conditions might get less hostile at the end of the
period, it is uncertain how much will be left of Fiona at that time
to take advantage of that change, with some suggestion in the global
models that Fiona could decay to a remnant low by then.  Thus,
the new NHC intensity forecast is a bit lower than the previous one,
near a model consensus than excludes the GFDL (which has looked
consistently too high).

A timely AMSR2 pass helped show that Fiona has sped up, and is now
moving 300/9.  Fiona should move around the Atlantic subtropical
ridge for the next few days.  The biggest change to the track
guidance is that all of the models have shifted a few degrees
westward at long range.  This appears to be due to less of a trough
forecast over the central Atlantic and a weaker representation of
Fiona in the global models, both of which would cause the storm to
continue moving northwestward for a longer period of time.  The new
NHC track forecast follows the trend of the models, but remains a
fair distance east of the model consensus at days 4 and 5 due to
continuity constraints.  It would not be surprising if further
westward adjustments had to be made later today.


FORECAST POSITIONS AND MAX WINDS

INIT  19/0900Z 17.6N  42.7W   40 KT  45 MPH
 12H  19/1800Z 18.2N  44.0W   40 KT  45 MPH
 24H  20/0600Z 19.1N  46.0W   35 KT  40 MPH
 36H  20/1800Z 20.2N  48.1W   35 KT  40 MPH
 48H  21/0600Z 21.3N  50.3W   30 KT  35 MPH
 72H  22/0600Z 23.5N  54.8W   30 KT  35 MPH
 96H  23/0600Z 26.0N  57.5W   30 KT  35 MPH
120H  24/0600Z 28.0N  59.0W   30 KT  35 MPH

$$
Forecaster Blake
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