I'm always amazed at the number of really neat things NOAA provides to us in the way of navigational, tidal and weather information to name a few. One of the fun and very useful projects for the Chesapeake is mapping of that pesky jelly fish/sea nettle. So, check this out as you're contemplating a dip or other water immersion fun:
http://chesapeakebay.noaa.gov/forecasting-sea-nettles//
http://chesapeakebay.noaa.gov/forecasting-sea-nettles//