Oahu is in the clear but Kauai and Niihua remain under a flash flood watch through late tonight, according to the National Weather Service.

Forecasters said a strong low aloft and abundant moisture in the atmosphere is creating unstable weather conditions and the threat of heavy showers and thundstorms to Kauai County. A flood watch issued earlier today for Oahu has been lifted.

With the ground saturated from earlier rainfall, the runoff from heavy rains will be higher than normal, increasing the potential for flash flooding and landslides, the weather service said.

Flooding closed Kahuna Road east of Hula Road and Kawaihau Road near the Kahuna Road intersection in Kapaa Thursday night.

In Hanamaulu, heavy rain Wednesday night caused the sewer pump station to exceed its capacity, leading to about 1,000 gallons of sewage being released onto the ground. From there it flowed down a slope along the northeastern end of Hanamaulu Road and possibly reaching the valley above the beach park. Waste-water crews worked through Thursday morning to clean up.

The state Department of Health’s Clean Water Branch issued a warning for residents to say out of Hanamaulu Stream and Bay.

The weather service says tradewinds have returned to Maui County and the Big Island. But hot and humid weather is forecast to continue for Oahu and Kauai through the weekend.

The weather system west of Kauai blamed for the unstable weather over Kauai and Oahu is expected to eventually weaken and move away, bringing cooling tradewinds back. But forecasters say that may not happen until next week.