Arthur is churning up big waves all along the Atlantic coast, changing the way water moves near shore.
Ocean City beach patrol officials warned dangerous rip currents are possible, and that those rip currents could be especially troublesome if sunny skies on Saturday - once the storm has passed - draw lots of people to the water.
About 100 people each year in the U.S. drown because of rip currents, and about 80 percent of swimmers who must be rescued in the ocean are caught in them, according to the United States Lifesaving Association, a nonprofit lifeguard group.
Here are five things to know about rip currents:
WHAT IS A RIP CURRENT?
A rip current is a channel of water that flows out into the ocean from shore. The motion and waves of the ocean are constantly changing the sand on the bottom. Water going back out to sea takes the shortest path and sometimes all that water flows into a narrow area, like a depression between two sand bars, creating a rip current that can pull swimmers away from shore. Rip currents can be anywhere from about the length of a car to over half a football field.
IS IT THE SAME AS AN UNDERTOW?
It is not an undertow. A rip current will pull swimmers out to sea, but won't pull them under. The currents are temporary and follow the dips and rises of the ocean floor instead of a constant flow. That's why the term "rip tide" is a misnomer, because tides are caused by the gravitational pull of the moon.
WHAT IF YOU GET CAUGHT BY A RIP CURRENT?
If you have a boogie board or other flotation device, hold on, lifeguards advise. The current won't pull you under. Instead, ride it out. The water will eventually stop pulling out. Or, swim parallel to shore to get out of the rip current. But don't swim against it. Some rip currents flow at 8 feet per second, which is faster than Olympic swimmers.
IS IT SAFE TO SWIM ONCE ARTHUR PASSES?
It could be a dangerous day at the beach even with Hurricane Arthur moving away. The churning waves from the storm will create new sandbars and depressions, causing rip currents to pop up suddenly.
HOW CAN I STAY SAFE?
Experts suggest it is always best to swim near a lifeguard stand. Also, talk to lifeguards, who can tell you how bad conditions are before you get in the water. And listen to their advice: Stay close to shore, where you can manage yourself in the waves.