By 2050, much of U.S. coastal areas are likely to be threatened by 30 or more days of flooding annually because of dramatically accelerating impacts from sea-level rise, according to a new National Oceanic and Atmospheric Administration (NOAA) study.The findings appear in a paper entitled “From the Extreme to the Mean: Acceleration and Tipping Points for Coastal Inundation due to Sea Level Rise” and follows an earlier study by the report’s co-author, William Sweet, Ph.D., a NOAAA oceanographer.