NHC has changed the Watch and Warning criteria for Tropical Storms and Hurricanes effective June 1,2010.

National Hurricane Center to Increase Lead Time in Watches and Warnings

The National Hurricane Center (NHC) will provide greater lead time for tropical cyclone watches and warnings beginning with the 2010 hurricane season. With the ever-increasing population along the United States coastline, communities need more time to prepare for tropical cyclones. Advances in observational capabilities, numerical weather prediction, and forecaster tools over the past two decades have enabled the NHC to make more accurate track forecasts. Over the past 15 years, average NHC forecast track errors have been cut in half. As a result of this progress, tropical storm and hurricane watches and warnings for threatened coastal areas will be issued 12 hours earlier than in previous years.

New Definitions of Tropical Storm and Hurricane Watches and Warnings for 2010

Tropical Storm Watch: An announcement that tropical storm conditions (sustained winds of 39 to 73 mph) are possible within the specified coastal area within 48 hours.

Tropical Storm Warning: An announcement that tropical storm conditions (sustained winds of 39 to 73 mph) are expected somewhere within the specified coastal area within 36 hours.

Hurricane Watch: An announcement that hurricane conditions (sustained winds of 74 mph or higher) are possible within the specified coastal area. 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.

Hurricane Warning: An announcement that hurricane conditions (sustained winds of 74 mph or higher) are expected somewhere within the specified coastal area. Because hurricane preparedness activities become difficult once winds reach tropical storm force, the hurricane warning is issued 36 hours in advance of the anticipated onset of tropical-storm-force winds.

http://www.nhc.noaa.gov/watchwarn_changes.shtml

Other Changes:
http://www.nhc.noaa.gov/pns_index.shtml