The National Weather Service has issued an advisory Wednesday for high surf and a high risk of dangerous rip currents along ocean beaches on the south coast of the Vineyard.

Tropical Storm Bertha is expected to pass within 300 miles south of Massachusetts, which will bring large wave swells and a high risk of rip currents along the southern coast of the state. The risk was in effect from 8 a.m. Wednesday through the evening, the National Weather Service said.

Surf height Wednesday is expected to be six to eight feet. High tide along the south shore runs from mid to late afternoon.

Trustees of Reservations Vineyard superintendent Chris Kennedy said staff are warning visitors to Norton Point and Long Point about the high surf and currents, and signs are also posted at Wasque. The Trustees are urging people to visit East Beach instead.

Edgartown parks administrator Marilyn Wortman said that as of 1:30 p.m. Wednesday, there were no rip currents reported at South Beach. Life guards are checking regularly, she said.

Rip currents are powerful channels of water that flow away from the shore, the National Weather Service said, and they occur most often at low spots, breaks in the sandbar and in the vicinity of jetties and piers. Rip currents can be life threatening, and beachgoers are advised to pay attention to surf conditions, lifeguards and posted signs.

The Massachusetts Emergency Management Agency advises those caught in a rip current not to swim against the current, but instead to swim parallel to the beach to an area where the current is weaker. Those who cannot escape the current are advised to tread water or float and to call or wave for assistance.