Weather.Unisys - Check out their 6-panel display of the US pressure fronts and precipitation, in 12-hour intervals, AND forecasts out to five days.
Upper Chesapeake wind nowcast & forecast from NOAA - very accurate 24 hour predictions as part of the Chesapeake Bay Operational Forecast System.
Thomas Point Light - current wind, water temp and other data from the National Data Bouy Center. The anemometer at TPL is 18m above sea level so it may not reflect accurate readings for wind at sea level.
National Airport - wind readings for Washington Sailing Marina on the Potomac River
Windfinder - European site that has expanded with US wind and surf data and forecasts.
Sea Nettle Tracking - aka what are my chances of getting stung by a jellyfish?
The Chesapeake Bay Environment
Eyes on the Bay is using new monitoring technologies and traditional programs to better understand the health of Maryland's water and habitat quality. Check out their website.
Earth911 and especially their Beach Water Quality information.
The Chesapeake Bay Program
Mid-Atlantic Coastal Beach Sampling
Surf Rider Foundation
Water Quality and Beach Closures - it's always a good idea to check for water contact advisories before you go out, especially mid-summer or after a big storm.
Anne Arundel County
Baltimore County - Gunpowder is listed as Hammerman Beach on this site.