Many Oahu homeowners and businesses along the south shore from Kaena Point to Koko Head face the potential of paying more than 350 percent in additional flood insurance premiums, under revised federal risk maps.

But state and county officials said some residents could reduce potential premiums by buying flood insurance at “;grandfathered”; rates before the revised maps become effective probably in a year.

The revised maps may be viewed starting tomorrow at the city's data access branch on the first floor of the Frank Fasi Municipal Building or at the state National Flood Insurance Program Web site at hidlnr.org/eng/nfip.

The revised assessment of flood risks, prompted by federal officials after Hurricane Katrina, has been completed in Maui County and is undergoing review of preliminary maps starting this month on Oahu and Kauai.

The Federal Emergency Management Agency, revising the maps, is still working on the preliminary maps for the Big Island.

The revisions are the first major comprehensive change in flood maps on Oahu in more than 20 years.

State and county officials along with FEMA plan to hold a coordination meeting on Aug. 27 to officially start the 90-day period in which Oahu property owners can appeal flood risk assessments.

Carol Tyau-Beam, the state National Flood Insurance Program coordinator, said in certain instances, people who do not have flood insurance will have to buy flood insurance if they have a federally backed mortgage.

Tyau-Beam said the final flood maps will probably be completed in a year.

She said her office is trying to provide information to residents so that they may be able to buy the flood insurance at more favorable “;grandfathered”; rates in advance of the revised maps.

“;We're trying to do outreach,”; she said.

Tyau-Beam said the grandfathered policy could also be transferable to new owners.

Tyau-Beam, state National Flood Insurance Program coordinator, said flood insurance premiums could be raised to $6,000 from $1,300 annually.

Mario Siu-Li, the city National Flood Insurance Program coordinator, said many properties from Ala Moana to Hawaii Kai have been added to the flood hazard map.

Siu-Li said the revised maps will reduce the flood requirements for some Ewa Beach residents but increase the requirements for some residents along the eastern coastal border of Kuliouou.

He said some places in flood zones may have to build new structures 2 to 3 feet higher than the current requirement.

“;Basically, I think everybody will have to reassess their need for flood insurance in particular,”; he said.

Siu-Li said the maps are preliminary and subject to change by FEMA.

A meeting to review the revised Maui flood maps is scheduled from 2 to 8 p.m. tomorrow at the Kihei Community Center.

Maui planners estimate that annual insurance premium savings for residential properties can be as much as 427 percent if they are grandfathered in at the lower risk classification, while commercial structures can realize savings up to 640 percent.