The first round of 2007 March thunderstorms will hit O'ahu this afternoon, according to the National Weather Service.

Heavy showers and large surf are in the forecast through tomorrow, and a flood watch was in effect for Kaua'i and Ni'ihau through early this morning.

"The potential for heavy rain is great," said National Weather Service lead forecaster Tom Birchard.

Birchard said a slow-moving cold front is making its way through the Islands, starting with Kaua'i and moving to O'ahu, then to Maui and the Big Island.

Winds will be out of the south and southwest before shifting west, so all of O'ahu is expected to get rain, he said.

A low front driving the storm also is creating a northwest swell, with big waves expected at 4 this morning and rising throughout the day.

"We're expecting faces 25 to 30 feet with higher sets offshore, peaking Wednesday," Birchard said.

One Civil Defense official said the state is better prepared this year should there be a repeat of the rain of last March, which ushered in more than 40 days of downpours and made the season the wettest in 55 years.

"Hopefully, last March was one for the record books and we won't have to revisit it again, but if we do, the city gained so much valuable working experience from the floods last year and has been able to apply a lot of the lessons learned to disaster planning," said John Cummings, spokesman for the Department of Emergency Management.

The biggest difference is that city officials have a response plan, approved by the City Council and state Civil Defense, he said.

Heavy rain started in February last year and continued through March, causing rockslides, flooding, sewage spills that closed beaches, and heavy damage to agriculture statewide, amounting to millions of dollars worth of damage.

Rain also contributed to the breaching of a dam on Kaua'i that killed seven people.

Reach Rod Ohira at rohira@honoluluadvertiser.com.