The National Weather Service extended a high surf warning through Thursday night because of a new giant swell arriving Wednesday that could bring more 50-foot waves to north shores of Oahu and other islands.

No major problems were reported today from the current declining swell. However Oahu lifeguards reported 24 rescues on the North Shore, 22 of them at Waimea Bay.

The high surf warning for north- and west-facing shores of Oahu, Kauai County and Molokai; and the north-facing shores of Maui and the Big Island is now in effect until 6 a.m. Friday.

Surf on the north shores of most islands declined today to still-giant levels of 30 to 40 feet today from the nearly 55-foot sets seen Monday. North shores of the Big Island were expecting wave faces of 20 to 30 feet. The west-facing shores of Oahu and Molokai saw 18- to 25-foot surf.

Forecasters said the current swell should drop below advisory levels on Wednesday, however wave heights will rise rapidly Wednesday night as a new giant swell arrives and peaks on Thursday.

North shore wave heights will lower to 12 to 18 feet Wednesday, then rise rapidly Wednesday night to heights of 40 to 50 feet. West shores of Oahu and Molokai should see wave heights decline to 8 to 12 feet Wednesday before rising to 20 to 25 feet late Wednesday night. North shores of the Big Island should expect surf to decline to 10 to 15 feet Wednesday, before rising again to 20 to 25 feet Thursday.

A spokeswoman for the Ocean Safety Division said surfing conditions improved as the swell dropped, allowing surfers to catch some of the giant swell on the North Shore.

Lifeguards reported a number of broken boards and leashes. Lifeguards on rescue watercraft rescued 20 surfers from the surf at Waimea and two bodyboarders from the shore break. Two other people were rescued at other North Shore beaches and lifeguards issued1,180 warnings to beachgoers.

West shore lifeguards did not report any rescues, but issued 600 preventative actions.

Haleiwa Beach Park, Alii Beach Park and Waimea Bay Beach Park reopened Tuesday morning after no major problems were reported this morning, following wave run-up that flooded parking areas Monday. However, the restrooms at Waimea are closed while city crews worked to empty a septic tank.

Keawaula Bay, also known as Yokohama Bay, in the Kaena Point State Park remained closed today because of high surf.

On the Big Island, Old Government Beach Road in Waa Waa briefly reopened before the county closed it again because of surf this afternoon. The county also closed Laaloa, Kahaluu, Mahukona (wharf side) and Kekaha Kai (Kua Bay section) beach parks today.

Surf of more than 50 feet Monday washed over roads and threatened a home on Kamehameha Highway at Sunset Beach. Minor flooding was reported at a paddle-board rental area at a Haleiwa surf shop. The surf also undermined the foundations of two lifeguard stations at Laniakea and Chun’s Reef.

The city closed Kamehameha Highway on the North Shore to all but residents Monday afternoon, keeping tourists away from the hazardous waves.

The surf still kept lifeguards on Oahu busy on north, west and east shores.

A wave knocked a lifeguard off an all-terrain vehicle as he rode to warn beachgoers on the North Shore about the dangerous surf conditions.

Lifeguards on exposed east shores like Sandys and Makapuu reported waves as high as 24 feet. Lifeguards reported 115 rescues and 1,250 preventative actions at east beaches.

Lifeguards rescued six people and issued 1,000 warnings on west-facing beaches, and North Shore lifeguards warned 950 people about the surf.

Surf on the North Shore was too big and choppy for even professional surfers to ride.

Because the current swell was generated by a storm closer to the islands than usual sources, the waves overlapped and created a greater-than-normal run-up on shore.

The world’s best big wave surfers were notified Tuesday that the Quiksilver in Memory of Eddie Aikau big wave surf contest is on a green alert because of the upcoming swell. A decision on whether to run the event will be made Thursday morning, if the surf shows up as expected.

Organizers said however, there is a concern that the surf could be too big and dangerous to hold the competition.

Waves from the new swell could be even larger than the choppy, 55-foot surf that hit the North Shore on Monday.

If the Eddie is not a go, another giant swell is forecast to arrive starting Sunday or Monday and peaking Tuesday.

But the holding period for the Eddie lasts only until Monday, so that swell could arrive one day too late to hold the contest.