GFDL/NOAA Hurricane Emily Forecast Video:
----------------------------------------

This video illustrates the GFDL forecast system results for Hurricane
Emily, which threatened the east coast of the U.S. in late August and
early September 1993. The GFDL system employs a multiply-nested
moveable mesh hurricane model and the forecast shown here is one of 36
Atlan tic cases run semi-operationally at GFDL in 1993. The GFDL system
was the first to give an indi cation, several days in advance, of the
movement of Emily toward the coast of North Carolina and its subsequent
northeastward recurvature just offshore of Cape Hatteras. The numerical
model which forms the heart of the system is the first model capable of
forecasting both the track and intensity of hurricanes, and the system
performed exceptionally well for the 14 forecasts of Hurricane Emily in
1993. Based on these results, and similar successes in 1994, the GFDL
model has been chosen to become the official hurricane prediction model
at the National Meteo rological center for the 1995 hurricane season.

The case illustrated in the video is from a forecast made on GFDL's
Cray YMP/8 supercomputer, which consumed approximately 6 hours of
computer time. (Analogous runs of the multitasked version of the model
on 12 processors of NMC's Cray C90 use only about 15 minutes of
computer time.) The times shown are for the 24 - 60 hour period of a
forecast initiated on August 30, using data taken during the time that
the storm was approaching the Carolina Coast. The loop displays the 350
K 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 dependant on warm, moist tropical oceans and
cumulus heating. The red cones indicate wind speed and direction, and
are shown only where wind speeds exceed gale force.

The first loop is taken from a perspective looking toward the United
States coastline. The second loop is taken directly above and shows
spiral ripples in the upper levels above the Hurricane sys tem and the
relatively warm and moist eye and storm core. The third loop is looking
southeast toward the approaching storm. Note the inward spiraling of
the equivalent potential temperature surface at low levels,
representing an energy source for the storm. This inflow of thermal
energy decreases, at first from the northwest as cooler drier air is
entrained, then in all storm quadrants, as the storm moves
northeastward away from the US coast and out over cooler ocean waters.