NEW WATCHES, WARNINGS FROM STORM CENTER
The National Hurricane Center is testing three new products this hurricane season to help keep you safe and informed.
First, the center and National Weather Service will issue storm surge watches and warnings to highlight areas that have a significant risk of life-threatening flooding from a tropical system. Storm surge is often the greatest threat to life and property from a tropical storm or hurricane, and it doesn’t always occur at the same times or locations as a storm’s hazardous winds.
Evacuations are generally needed to keep people and pets safe from storm surge. Having separate warnings for wind and storm surge may save lives by better identifying specific hazards communities face, and by enhancing public response to instructions from local officials.
A storm surge watch is the possibility of life-threatening flooding from rising water moving inland from the shoreline, generally within 48 hours, from a tropical storm or hurricane approaching the location. A storm surge warning is the likelihood of life-threatening flooding from rising water moving inland from the shoreline, generally within 36 hours, from a tropical storm or hurricane. A watch or warning may be issued earlier when other conditions, such as the onset of tropical stormforce winds, are expected to limit the time available to evacuate.
Also beginning with the 2017 hurricane season, the National Hurricane Center may issue advisories, watches and warnings for disturbances that are not yet a tropical depression or tropical storm but which pose the threat of bringing tropical storm or hurricane conditions to land areas within 48 hours.
Previously, it has not been permitted to issue a hurricane or tropical storm watch or warning until after a tropical depression or tropical storm had formed. Advances in forecasting over the past decade or so, however, now allow the confident prediction of tropical cyclone impacts while these systems are still in the developmental stage.
Finally, the arrival of sustained tropical-storm-force winds is a critical planning threshold for coastal communities, as many preparedness activities become difficult or dangerous once winds reach tropical storm force. Frequently, this timing is estimated using the “center line” of the hurricane center track, intensity and wind-field (size) forecasts, but such an approach doesn’t account for forecast uncertainty.
Communities can be caught offguard if a storm speeds up or grows in size beyond what was forecast. To provide guidance on when users should consider having their preparations completed before a storm, NHC will begin issuing experimental time of arrival of tropical-storm-force winds graphics in 2017.
The primary graphic displays the “earliest reasonable” arrival time, identifying the time window that people can safely assume will be free from tropical-storm-force winds. A second graphic will show the “most likely” arrival time – that is, the time before or after which the onset of tropical-stormforce winds is likely.