Friday, April 05, 2013

NWS Formally Approves Broader Hurricane Warning Definition

As first talked about back in December, the National Weather Service and the National Hurricane Center have broadened the definition for hurricane and tropical storm watches and warnings.  The broader warning definition will now include watches and warnings to be issued or remain issued after a tropical system transitions to a nontropical or post-tropical entity.

An example of what that would look like as an advisory has been produced by the National Hurricane Center for reference, along with more detail in the definition process.

The updated definition is due in large part by Sandy and the transition the storm made from tropical to post-tropical in the hours before landfall.  Last October, the decision was made between the NHC and NWS to not issue hurricane warnings along the coast as the storm was projected to not be tropical at landfall.  The Sandy scenario was the first such scenario forecasters had faced and while they technically were accurate in handling the warning scenario, there was a good bit of consternation among many in the meteorological community over what was perceived to be a downplaying of the storm.

“Our forecasters now have more flexibility to effectively communicate the threat posed by transitioning tropical systems,” said Louis W. Uccellini, Ph.D., director of NOAA’s National Weather Service in a statement on the NHC website. “Sandy’s forecast was remarkably accurate and under a similar situation in the future, forecasters will be able to choose the best option to underscore the urgency involved."

The warnings and watches otherwise remain as is -- hurricanes for winds or projected sustained winds over 74 miles per hour, tropical storm warnings for winds between 39 and 73...the only difference is the inclusion of the post-tropical (non-tropical) storm.