The FAA (Federal Aviation Admin.) has issued a flight advisory regarding possible unreliability of GPS signals along the SE Atlantic coast, North Carolina to Florida (and Gulf of Mexico). The advisory is linked HERE
According to the advisory, tests having a duration of about 45 minutes over the stated dates have the potential to interrupt or introduce errors in GPS signals.
If you're going to be offshore, you might want to be sure you have careful plots on your paper charts. We went through this off the coast of Central America many years ago, and those boats that relied entirely on their GPS and plotters were really thrown for a loop when the GPS signals were interrupted periodically for more than a week.
This is not the end of the world, and it affects aircraft a lot more seriously than it does boats, but it's worth staying alert.