Periods of heavy rain and hazardous ocean conditions continued today across parts of Hawaii, with the greatest flood risk focused on Kauai and Niihau as wet weather lingers into midweek.

The National Weather Service said a lingering weather system west of the islands is continuing to pull warm, moisture-heavy air northward, keeping showers in the forecast through at least early Tuesday. Some areas of Kauai and Oahu picked up another 1 to 2 inches of rain overnight, adding to already saturated ground from the weekend.

Forecasters said the flood watch remains in effect through late tonight for Kauai, Niihau and Oahu as even moderate rainfall could quickly turn into runoff. Flooding is most likely in low-lying areas, along streams and on roads that typically collect water.

While rainfall may be lighter than Sunday’s downpours, forecasters warned that slow-moving showers could linger over the same areas, raising the risk of flooding for streets and streams. Isolated thunderstorms are also possible, mainly over Kauai and Oahu, through early Tuesday.

Looking ahead, the flooding threat is expected to ease for Oahu by early Tuesday, but Kauai and Niihau could remain at risk through the middle of the week. Another cold front approaching from the northwest is forecast to stall near those islands, keeping skies mostly cloudy with periods of rain. Officials said flood watches may need to be extended for the western islands if conditions worsen.

Conditions should gradually improve late in the week, with fewer showers expected by Thursday and Friday. Tradewinds are forecast to return over the weekend, bringing drier air and more typical weather heading into the holiday week.

At the same time, dangerous surf remains a concern statewide. A large north-northwest swell is producing advisory-level waves along north- and west-facing shores. Surf heights of 15 to 20 feet along north-facing shores and 10 to 14 feet along west-facing shores are expected to continue through this evening for Niihau, Kauai and Oahu, before slowly easing.

High surf advisories remain in effect into early Tuesday for Molokai, Maui and parts of Hawaii island, where an earlier warning was downgraded as surf heights came in lower than expected. Ocean safety officials continue to urge the public to stay out of the water if conditions appear unsafe.

Marine conditions are also rough, with a small craft advisory in effect through 6 p.m. today for waters around Kauai and Oahu. Seas of 7 to 10 feet are making conditions hazardous for smaller boats, especially for inexperienced mariners.

Residents and visitors are urged to monitor forecasts closely, avoid flooded roads and heed all ocean and marine advisories.

UPDATE: 6:45 p.m.

The flood watch for Kauai, Oahu, and Niihau remains in effect until late Monday night, according to the National Weather Service in Honolulu.

”A cold front stalling over the western Hawaiian islands through Monday will increase rainfall activity across the western half of the state,” the updated flood watch says. “These showers may become locally heavy at times with isolated thunderstorms.”

NWS forecasters said “flood-prone roads and other low-lying areas may be closed due to elevated runoff and overflowing streams. Urban areas may receive more significant flooding and property damage due to rapid runoff.”

Forecasters said that a front that has stalled out near Oahu “will hold its position through the afternoon before moving slowly back to the north and west tonight and Monday. This will bring continued chances for moderate to heavy rain to the western end of the state through tomorrow. “

They said the chance of rain will decrease Monday night into Tuesday, but returns Tuesday night into Wednesday “as the remains of the current front fuse with a new one and they move back into the western part of the state.”

However, the weather service forecasters note, “Confidence in location is not as high with this next system, as guidance has trended away from bringing it as far east as Oahu.”

Heavy rain across Oahu today causes localized flooding, including on Queen Street, which which was shut this afternoon between Ward Avenue and Kamakee Street.

3:42 p.m.

The flood advisory of Oahu will expire at 3:45 p.m. today.

Radar indicates that heavy rain has diminished for now, so the flood advisory has been canceled.

Meanwhile, a flood watch remains in effect until 6 a.m. Tuesday for Oahu, Kauai and Niihau.

2:30 p.m.

A high surf warning has been issued for the west-facing shores of leeward Hawaii island, while a high surf advisory has been issued for the north- and west-facing shores of Oahu, Kauai, Molokai and Niihau, and the north-facing shores of Maui.

A large, medium period west-northwest swell between 290 and 300 degrees is building this afternoon along portions of the north- and west-facing shores. Surf is expected to peak late this evening then gradually lower Monday afternoon.

The high surf warning for leeward Hawaii island is in effect from 6 a.m. Monday to 6 a.m. Tuesday. Expect dangerously large breaking waves of up to 12 feet. Surf will build late tonight and peak Monday afternoon.

“Stay away from the shoreline along the affected coasts. Be prepared for road closures. Postpone entering or leaving channels affected by the high surf until the surf subsides,” forecasters report.

EARLIER COVERAGE

Oahu is under a flood advisory until 3:45 p.m. today following flooding caused by excessive rainfall.

“Ponding of water in urban areas is likely. Minor flooding on roads, poor drainage areas, and in streams. Some low-water crossings may become impassable,” according to National Weather Service forecasters.

At 12:50 p.m. today, the radar indicated areas of heavy rain developing and traveling northeast of Oahu.

“While there may be a brief lull in rainfall, a larger batch of showers is moving up from the southwest and is expected to impact the island for the next few hours,” according to forecasters.

Rain was falling at a rate 0.5 to 1.1 inches per hour with the possibility of 2 inches per hour. The entire island of Oahu is expected to experience flooding, according to NWS.

The advisory may be extended beyond 3:45 p.m. if flooding persists.