Oahu starts to dry out, but flood threat remains for Kauai, Niihau

UPDATE: 3:50 p.m.

Oahu is no longer under a flash flood watch, but the advisory remains for Kauai and Niihua through Thursday afternoon, the National Weather Service said.

“Low pressure northwest of the islands will produce unstable and very moist conditions over Kauai and Niihau, leading to periods of heavy showers and thunderstorms,” the weather services’ advisory said at 3:24 p.m. today. “With abundant rainfall having already soaked the islands, additional heavy rain could lead to flash flooding.”

The forecast for the islands calls for “wet and unsettled weather pattern over Kauai county and Oahu through tonight, with rain, heavy at times, and a chance of thunderstorms.”

Forecasters said some areas of Maui County may also see rain but the Big Island will be mostly dry.

“As the low moves away Thursday and Friday, drier conditions will move in from the east, and a somewhat less humid, more seasonable trade wind weather pattern will prevail over most areas by the weekend,” forecsters said.

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The unsettled weather is expected to continue over Kauai County and Oahu through tonight, according to weather officials, bringing heavy rain at times, and a chance of thunderstorms.

A flash flood watch for Niihau, Kauai and Oahu is in effect through this afternoon. A brown-water advisory is in effect for Oahu.

Forecasters from the National Weather Service said a complex area of low-pressure northwest of the isles will continue to draw abundant moisture over Oahu and Kauai County while also providing instability, bringing periods of rain and a chance of thunderstorms. The additional heavy rain could lead to flash flooding.

Some areas of Maui County may get some wet weather today, as well. The Big Island will remain mostly dry.

The state Department issued a brown-water advisory for Oahu as a result of stormwater runoff entering the ocean.

“The public is advised to stay out of flood waters and storm water runoff due to possible overflowing cesspools, sewer, manholes, pesticides, animal fecal matter, dead animals, pathogens, chemicals, and associated flood debris,” the advisory said. “Not all coastal areas may be impacted by runoff, however, if the water is brown stay out. Continue to practice good personal hygiene and follow-up with your primary care physician if you have any health concerns.”

As the low moves away Thursday and Friday, drier conditions will move in from the east, and a somewhat less humid, more seasonable tradewind weather pattern will prevail over most areas by the weekend. Trades will likely be lighter than the summertime average, however, as the trough of low pressure lingers.

Record rainfall of 4.2 inches, meanwhile, was recorded in Honolulu on Tuesday, breaking the old record of 0.14 inches set in 1994. Additionally, the NWS said this marks the wettest June day on record in Honolulu.

Tuesday’s single-day rainfall total was also one of the top 25 wettest days on record at Honolulu. It holds the distinction among days on the top 25 list that in that it did not occur during the typical wet season from October through April.