GFDL/NOAA Hurricane Fran Forecast Animation:
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This animation illustrates the GFDL forecast system results for
Hurricane Fran, which struck the east coast of the U.S. in early
September 1996.  The GFDL system employs a multiply-nested move-able
mesh hurricane model.  Based on its initial performance in the 1993 and
1994 hurricane seasons, the GFDL model was chosen as the official
hurricane prediction model at the Centers for Environmental Prediction
(NCEP, formerly the National Meteorological Center) beginning with the
1995 hurricane season.  It has consistently outperformed earlier
hurricane prediction models in terms of track and intensity.

The case illustrated in the animation is from a forecast made on GFDL's
Cray T90 supercomputer which was a duplicate of the operational,
real-time run made on the NCEP Cray C90 supercomputer.  The times shown
are for the 3-36 hour period of a forecast initiated on September 5,
using data taken during the time that the storm was approaching the
Carolina Coast.

The first loop displays the 350K isosurface (light-colored sheet) of
"equivalent potential temperature", which measures the combined effects
of heat and moisture and is therefore a fundamental quantity of
hurricanes, a heat engine-like phenomena dependent on warm, moist
tropical oceans and cumulus heating. The red cones indicate wind speed
and direction near the earth's surface and the magenta cones indicate
the winds at the outflow region near the top of the storm. The box of
white lines at the start of the sequence depicts the computational grid
of the innermost nest of the nested numerical model.  Note how the
storm intensity decreases after it makes landfall, as indicated by the 
shrinking of the warm core. The distinctive inward spiral pattern in the 
surface winds, however, persists long after landfall.

The second sequence shows the predicted precipitation pattern during
the hurricane's evolution, with the most intense rainfall indicated by
the red shades. The tendency of the heaviest precipitation to take
place on the north side of the storm is in good agreement with
observation from land-based radars.  The surface wind vectors are also
shown and, in this case, are color coded: white for hurricane force,
magenta for gale force, and yellow for winds less than gale force.
Note the calm in the eye of the storm, and the reduction in wind speeds
after landfall as a consequence of increased friction over land
surfaces and overall strom decay.