"The public is advised to stay out of coastal waters impacted by storm water runoff that may contain debris and possible sewage and chemical contamination," said Watson Okubo, supervisor for the Clean Water Monitoring Section of the Department of Health, in a news release.

"Heavy rains are expected today, tonight, and into Saturday. Streams may overflow their banks and flooding may result. The public should stay out of all flood waters due to possible sewage, chemical, and leptospirosis contamination."

The threat of heavy rain also has postponed this weekend's Sunset on the Plains celebration at Kapolei. It was rescheduled for next weekend.

The cancellation came as the state remains under a National Weather Service flash flood watch for today and tomorrow due to Tropical Depression Kenneth.

Heavy showers and thunderstorms are likely on all islands starting later today, which may lead to flash flooding, the weather service said.

Forecasters said it's a combination of moisture from Kenneth and increased instability from an upper level cold low pressure center that's causing increasing showers over the main Hawaiian Islands.

A flash flood watch means that flooding is possible but not imminent.

Civil defense and emergency officials are advising residents to take precautions.

On the Big Island, civil defense, police and fire officials met with Mayor Harry Kim yesterday to discuss strategies and preparedness.

"Everyone needs to be prepared," said Lanny Nakano, acting administrator for the Hawai'i County Civil Defense. "If you have had problems with flooding in the past, you need to be ready."