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NOAA broadens definition of hurricane and tropical storm watches and warnings

The Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Terra satellite acquired this image of Hurricane Sandy off the southeastern United States. The Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Terra satellite acquired this image of Hurricane Sandy off the southeastern United States.

NOAA's National Weather Service has announced that starting the beginning of this hurricane season (June 1)... the definitions of hurricane and tropical storm watches and warnings will be broadened to allow these watches and warnings to be issued or remain in effect after a tropical cyclone becomes post-tropical... if the storm poses a significant threat to life and property.

In addition... the National Weather Service would ensure a continuity of service by allowing the National Hurricane Center to issue advisories during the post-tropical stage.

These changes were motivated by the special challenges posed by Hurricane Sandy... which was forecast to evolve from a hurricane to a post-tropical cyclone prior to reaching the coast last fall.

The bottom line... this allows hurricane specialists at the National Hurricane Center to be more flexible in communicating the threat posed by transitioning tropical cyclones.

Sandy's forecast was remarkably accurate and under a similar storm situation in the future... forecasters will be able to choose the best option to underscore the urgency involved.

This change was first proposed during the NOAA Hurricane Meeting last November and has since been the focus of much discussion in the meteorological and emergency management communities... in forums such as the American Meteorological Society Annual Meeting in January and the National Hurricane Conference last month.

The change was also supported by preliminary findings from NOAA's service assessment on Sandy... which will be released in May 2013.

So... beginning 1 June... the following new National Weather Service watch/warning definitions will go into effect:

  • Hurricane Warning: An announcement that sustained winds of 64 knots (74 mph or 119 km/hr) or higher are expected somewhere within the specified area in association with a tropical, subtropical, or post-tropical cyclone. Because hurricane preparedness activities become difficult once winds reach tropical storm force, the warning is issued 36 hours in advance of the anticipated onset of tropical-storm-force winds (24 hours for the Western North Pacific). The warning can remain in effect when dangerously high water or a combination of dangerously high water and waves continue, even though winds may be less than hurricane force.

  • Hurricane Watch: An announcement that sustained winds of 64 knots (74 mph or 119 km/hr) or higher are possible within the specified area in association with a tropical, subtropical, or post-tropical cyclone. Because hurricane preparedness activities become difficult once winds reach tropical storm force, the hurricane watch is issued 48 hours in advance of the anticipated onset of tropical storm force winds.

  • Tropical Storm Warning: An announcement that sustained winds of 34 to 63 knots (39 to 73 mph or 63 to 118 km/hr) are expected somewhere within the specified area within 36 hours (24 hours for the Western North Pacific) in association with a tropical, subtropical, or post-tropical cyclone.

  • Tropical Storm Watch: An announcement that sustained winds of 34 to 63 knots (39 to 73 mph or 63 to 118 km/hr) are possible within the specified area within 48 hours in association with a tropical, subtropical, or post-tropical cyclone.

 

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