The National Weather Service has extended a flash flood watch for Oahu, Kauai and Maui counties until Tuesday afternoon.

A weather system northwest of the state is bringing moist air from the south and southeast, creating unstable conditions that could lead to more thunderstorms through Tuesday night, forecasters said.

"The combination (of moist air and the unstable atmosphere) is just very wet and it’s going to be persistant. It’s going to last for a while," said Jeff Powell, the lead forecaster for the National Weather Service.

Forecasters say the threat of thunderstorms will likely end Tuesday night, but wet weather will stick around and tradewinds may not return until later in the week.

A flash flood warning for Kauai expired at 9:30 a.m. It had been posted since early Sunday morning because of flooding on Kauai from persistant heavy rain.

The state Health Department issued a "brown water advisory," warning Oahu and Kauai residents to stay out of flood waters and storm water runoff due to the possibility of overflowing cesspools and sewer manholes and the presence of pesticides, animal fecal matter, dead animals, pathogens, chemicals and debris.

Rain created problems on both Oahu and Kauai all weekend and at least one death — a traffic fatality early Friday morning on the Pali Highway on-ramp off the H-1 Freeway — is blamed, at least in part, on the weather.

The state Division I high school baseball championship game was postponed until Monday night because of rain Saturday night.

Streams rose on Oahu and Kauai on Sunday, creating problems for some motorists because of road closures.

The Hanalei Bridge was reopened about 10 a.m. Monday, and both lanes of Kuhio Highway in Hanalei were reopened by 1:10 p.m. But Kauai County officials said traffic was "extremely heavy" and further flooding remains a possibility.

More than 11 inches of rain fell on the river in the 24-hour period ending at 2 a.m. and river waters remain high, the weather service said. Mudslides have also been reported Monday in Kapaa and Kalaheo, a Kauai County spokeswoman said.

Nearly 14 inches of rain fell on Mt. Waialeale; 10.6 inches was recorded at the Wailua Ditch; and 5.2 inches fell in Wainiha.

On Oahu, as much as 2 inches of rain an hour fell over the Koolaus Sunday and water flowed over Kamehameha Highway near Waikane.

Kahuku recorded  about 6.7  inches of rain over the 24-hour period ending at 2 a.m.; Punaluu got 6.1 inches; and Kahana recorded 5 inches.

Heavy rains over Hauula stranded drivers and forced the temporary closure of neighborhood landmark Tamura’s Market.

According to employee Charmaine Toelupe, rain flooded the area between the store’s warehouse and the front of the store, spoiling merchandise and forcing the store to shut its doors for more than two hours on what is traditionally the busiest day of the week.

Toelupe estimated the store lost between $10,000 and $15,000 in sales.

"Sunday is our busiest day and would have been even busier with Mother’s Day," Toelupe said. "People were waiting outside the door waiting for us to re-open."

Toelupe said the road outside the store was crowded with vehicles hemmed in by flooding in both directions.

"It’s never been this bad before," she said.