A riptide warning for south-facing beaches on Martha's Vineyard has expired, according to the National Weather Service. 

The warning was issued Monday morning, and remained in effect throughout the day.

In response to the warning, The Trustees of Reservations closed the beach at Long Point Wildlife Refuge to swimming for the day. Other Trustees properties remained open, Chris Kennedy, Vineyard superintendent for the Trustees, said.

Riptides are narrow, fast-moving ribbons of water that are capable of carrying swimmers who are unaware of the conditions far out to sea. On the Vineyard these currents are most likely to appear along the south shore, from South Beach in Edgartown to the remote, often private beaches up-Island. They are fickle and unpredictable and can change rapidly depending on the tides, currents and wind, but are at their most dangerous when the tide is high and conditions are rough.

If caught in a rip current, swimmers should not try to fight the current or swim against it. Instead, ride the current out by swimming parallel to shore until the rip subsides and you can safely make it in. If you are too tired to swim, float or tread water. Most riptides are not more than 30 feet wide.

The Trustees also warned Monday of reports of Portuguese man-of-wars along Norton Point Beach in Edgartown. In June large numbers of man-of-wars were found washed up on the south shore of the Vineyard this week, prompting The Trustees to post notices in the area. Though not uncommon, their arrival was earlier than expected. “They’re not uncommon, but we usually don’t see them until late summer,” said Mr. Kennedy at the time. “I think there may be a warm core eddy that is pushing them in.”

Beachgoers are advised to give the man-of-wars a wide berth of 30 to 40 feet, Mr. Kennedy said.