April 15, 2008 -- Hurricane forecasters are adopting a new system that lets them combine Doppler radar systems to watch a hurricane revving up in real time just before coming ashore.
The Vortex Objective Radar Tracking and Circulation (VOTRAC) system does what satellite imagery, aircraft and individual Doppler radars cannot by piecing together all the wind data on a storm every six minutes into a more complete and accurate picture of what as storm is doing.
This sort of data can provide critical warnings during storms -- such as last year's Hurricane Humberto -- in which the cyclones power up dangerously just before hitting land.
Because Doppler radars are regional and do not reach far out to sea, VORTRAC is perfectly suited to monitoring storms in the last hours before they strike land, say its developers at the National Center for Atmospheric Research (NCAR).
This also happens to be the point at which storm-tracking aircraft are less able to gather data, because they can't drop their instruments over land without endangering people on the ground.
"In general, they do not like to fly the reconnaissance aircraft over land," said Colin McAdie of the National Hurricane Center (NHC), where VORTRAC is being put to use to fill in that gap.
The definitive test of VORTRAC was when Humberto went from being a tropical storm to a hurricane in 19 hours and then came ashore near Port Arthur, Tex.
There was a six-hour blind spot between aircraft measurements of the storm, during which the hurricane quickly intensified. The then experimental VORTRAC spotted the storm revving up every step of the way.
"Last year it worked quite well," said McAdie. And so now it is becoming a regular part of the NHC's arsenal, he said.
"Humberto was just meandering around and didn't look like it was going to do anything, but then suddenly it intensified," said Paul Harasti of NCAR. He has worked on VORTRAC for more than a decade, using archived data to simulate what can now be measured in real time, he explained.
Another example of a storm in which VORTRAC might have been useful is Hurricane Charlie in 2004. That hurricane's wind speeds ramped up from 110 miles per hour to 145 miles per hour in six hours as it neared the coast of Florida.
"This (VORTRAC) information is a little too late for evacuation," said Harasti. "But it helps forecasters for flooding and wind damage."
It could also help people inland from coastal areas know what's coming, added NCAR's Michael Bell.
The beauty of VORTRAC, said Bell, is that it uses Doppler radar systems which are already in place. This means the same technique will also work in other parts of the world where Doppler radar systems are now or will soon be installed around the Indian and Pacific Oceans.
Related Links:
Larry O'Hanlon's blog: Earth Impacts