New flood insurance rate maps developed by the Federal Emergency Management Agency could lead to dramatic cost increases for some property owners on Oahu and Kauai.

But people can avoid higher rates, at least for a year, by renewing their flood insurance policies before the new maps take effect.

Flood insurance rates for a property in a low- to moderate-risk coastal area with a $350 yearly preferred risk policy could spike to up to $5,700 a year if it is bumped to a high-risk category when the new maps go into effect.

"That’s the worst-case example," said state National Flood Insurance Program coordinator Carol Tyau-Beam.

If the affected property is grandfathered, the property owner gets to continue the $350 rate for a year. Upon renewal, the policy will be converted to a standard policy of an estimated $1,500 per year, with annual increases of 10 percent.

"It’s more, but it’s way less (than the $5,700)," Tyau-Beam said.

The new flood maps take effect Nov. 26 for Kauai and Jan. 19 for Oahu.

Homeowners and business owners, especially those on the south coasts of the islands, are urged to attend public meetings on the new maps later this month. Experts will be on hand to discuss the map changes. Officials say properties on the south shores are at greater risk of damage based on a FEMA map study last year.

FEMA converted from paper maps, which were at least 20 years old, to a digital format several years ago. Slight changes were made in recent years as technology provided detailed typography of the islands. However, the upcoming revision is considered to be the first significant change in the last decade, FEMA Region 9 engineer Eric Simmons said.

Preliminary flood maps for Maui County are expected to be completed by early September. A date has yet to be set for the Big Island.

The new flood insurance rate maps are completely different from the state’s tsunami evacuation maps. Flood insurance rate maps are based on flooding that could be caused by a so-called "100-year storm," a rare severe weather event. The tsunami maps indicate areas that could be inundated by a seismic sea wave.

To avoid getting caught in a backlog, officials urge residents with a federally backed mortgage to call their insurance agent as soon as possible if they do not carry flood insurance and fall into a higher flood hazard area. Affected property owners who obtain flood insurance before the new maps go into effect will avoid higher insurance rates for a year.

Some of the areas on Oahu that will be affected by the map changes include Hawaii Kai, Waimanalo along Mekia Street, and the Brigham Young-Hawaii campus in Laie. On Kauai, Kapaa, Hanapepe, Poipu, Waimea and Kekaha will be affected.