A winter storm expected to reach the Islands today will shower the state with periods of heavy rainfall throughout the weekend, posing a threat of flooding, especially on O'ahu and Kaua'i.

The National Weather Service yesterday extended a statewide flash-flood watch from tonight through 4 a.m. Sunday.

"There's a threat for serious flooding across the Islands," National Weather Service forecaster Chris Brenchley said.

In Honolulu, the city's Department of Emergency Management urged residents to exercise extreme caution.

"Based on information we received from the National Weather Service this afternoon an area of unstable weather will develop off of Kaua'i, creating an intense period of heavy rains and possible flooding," Emergency Management Director Mel Kaku said in a news release. "The weather service modeling of these conditions shows that O'ahu and Kaua'i are in the primary threat and hazard area. We may begin experiencing the effects of this storm system beginning Friday morning with the heaviest showers and increased potential for flooding on Saturday night through Sunday morning."

Residents on O'ahu's windward coast could experience storm conditions similar to those seen during the 2006 March floods, including road closures, flooding and minor landslides, Kaku said. However, he added that the approaching storm is expected to pass through much quicker than the 2006 storm.