A 12-year-old boy swept away by a raging Kalihi Stream was rescued by helicopter Sunday afternoon and an elderly man was in critical condition after he was dragged into roiling water off Sandy Beach — with plenty more bad weather expected through midweek.

The entire state was placed under various flood warnings, watches and advisories on Sunday, but Kauai received the brunt of the unstable weather.

A landslide closed Kuhio Highway near Lumahai Beach. Flooding also forced the closure of Kuhio Highway near the Hanalei Bridge, among several other road closures on the Garden Isle. Power failures also were reported.

Rain fell at a rate of 2 inches per hour around Hanalei, and flooding forced about 12 residents from their homes along Wailani Road and Aloha Place in Koloa.

The wet weather is being driven by a moist and unsettled air mass over the western areas of the state, according to the National Weather Service. A front from the north has brought additional moisture.

The weather service reports that a strong surface high is moving to the far north-northeast of the islands, which should result in strong tradewinds in the later part of the week.

The host of advisories issued by the weather service Sunday included a flash flood warning for Kauai and Oahu and a coastal hazard message for the east shores of Kauai, Oahu, Maui and Hawaii island, with surf expected to build to 15 feet.

On Oahu, a fully clothed, elderly man — possibly a fisherman — was pulled into 6- to 8-foot waves off of Sandy Beach just before 1 p.m., witness Tim DeVault told the Star-Advertiser.

The man was dragged back to a lava outcropping by a relative and a bystander, who suffered cuts and scrapes while bringing the man back to shore, DeVault said.

The man also suffered a "huge gash" to the back of his head, DeVault said.

Paramedics took the man to an area hospital in critical condition. He is believed to be in his 60s or 70s, emergency services officials said.

But it was the helicopter rescue of a 12-year-old boy at Kalihi Stream that prompted Honolulu Fire Capt. Rick Karasaki to warn people about storm dangers over the next few days.

The boy had been hunting crayfish with friends at about 2:20 p.m. when he was swept to the other side of Kalihi Stream while Oahu was under a flood advisory.

"The kids are playing, the river rises and they all get away but one boy, who gets pushed by the water to the opposite side of the river," Karasaki said. "There was a forest behind him and a raging river in front of him. There was really no place to go and he couldn’t get back to safety."

A firefighter deployed from the fire department’s helicopter had the boy back to safety, unharmed, at 3:23 p.m., Karasaki said.

"This could have been way worse," Karasaki said. "The message here is we have to be aware that we have bad weather and need to stay away from rivers or anything that can change quickly. This boy was lucky, very lucky."

The weather service issued a flash flood watch for Kauai, Oahu and Niihau through this afternoon, which means conditions exist that can cause flooding.

Oahu’s North Shore also should see waves of 15 to 20 feet today, the weather service said.

Surf along east-facing shores should rise to 10 to 15 feet today and could increase Tuesday, when the northwest swell will turn to the north-northeast through Tuesday, forecasters said.

A high surf warning remains in effect for Kauai, Oahu, Maui and Hawaii island until 6 a.m. Tuesday.

The National Weather Service also issued small craft advisories for northwest, windward and leeward waters around Kauai; Kauai Channel; windward and leeward waters of Oahu; Kaiwi Channel; Maui County windward waters; Pailolo Channel; Alenuihaha Channel; and windward waters of Hawaii island.

The weather service warned that the weather pattern drenching the islands may persist into the middle of the week.