Residents are urged to use “;extreme caution”; today as heavy rain, flooding and flash flooding could hit parts of the state, authorities warned.

Oahu and Kauai face the greatest threat for widespread heavy rainfall, which could spread to the rest of the state tonight.

A flood watch, which took effect yesterday afternoon, will continue to tomorrow night.

Storm conditions could resemble those of a March 2006 storm—except for duration—that caused road closures, flooding and minor landslides, a city news release said.

In 2006 it rained for more than 40 days. Rainwater breached Kauai's Ka Loko Dam, killing seven people. On Oahu it led to a massive sewage spill in Waikiki that sent millions of gallons of raw sewage into the Ala Wai Canal.

While urging residents to use extreme caution, the city Department of Emergency Management also recommended that people who have experienced flood conditions in the past acquire sandbags and plastic tarps.

“;This looks to be the biggest rain producer of the winter season to date and we need to be prepared and aware of the hazards that floods and heavy rains can create,”; said Mayor Mufi Hannemann in a news release. While winter officially begins Dec. 21, typical winter weather has come early.

 

  Weather forecast

 

  Residents get ready for what could be major flooding. 

 

[  Watch  ]

 

 

 

 

The brewing storm was caused by the mixing of two less unusual events: a cold front to the west of Kauai and a southeasterly stream of air bringing moisture over the state.

The two conditions together create an unstable atmosphere.

It is like “;putting water on top of oil in a container,”; said Vladimir Ryshko, a meteorologist at the National Weather Service. “;Same thing happens.”;

By about 8 last night, moderate to heavy showers fell west of Oahu, and a line of heavy rain came down near Niihau, Ryshko said.

A flash flood watch means conditions might develop that lead to flash flooding, which could be deadly. But forecasters do not know how much precipitation might fall.

“;Flooding rain is possible, but we can't really pin things down,”; Ryshko said. “;The potential exists for heavy rain and damaging flooding.”;

He said narrow canyons and deep gorges would be dangerous places.