An official says she is concerned that as many as several hundred Oahu property owners affected by updated federal flood maps might be unaware of a looming deadline to lock in insurance at a lower rate.

Responding before Wednesday’s deadline could make the difference between paying $350 or $5,700 a year for flood insurance.

But so far, the official and insurers have not seen a rush of people attending informational meetings or updating their policies.

"I have much empathy," said state National Flood Insurance Program coordinator Carol Tyau-Beam. "It’s not cheap. Obviously that’s why we want to alert people to this grandfathering program."

The Federal Emergency Management Agency updated its flood-risk maps in recent years. As a result, several hundred parcels on Oahu were shifted into high-risk flood zones.

Those parcels are primarily along Oahu’s west and south shores, from Kaena Point to Portlock, as well as Mekia Street in Waimanalo and a small portion of Laie, said Mario Siu-Li of the city Department of Planning and Permitting.

In some cases, such as in Ewa Beach, properties were taken out of the high-risk zone, he said.

The new flood maps take effect Wednesday and affect people with federally backed mortgages. Property owners who act before Wednesday can be grandfathered in at current rates as low as $350 per year for one year, and could be eligible for discounted rates flood insurance rates after that.

(Their homes must have been built before Sept. 3, 1980, or built in compliance with the flood insurance rate maps in effect at the time of construction.)

Otherwise, people with federally backed mortgages could pay as much as $5,700 per year for flood insurance.

Tyau-Beam said she was concerned that only a few people attended the August informational meetings, which might indicate that many are still unaware of the FEMA map changes and the effect they will have on their flood insurance rates.

She said the grandfathering provision will provide some cost savings. "Otherwise, you’re going to be paying the higher rate," she said.

If someone has paid off their mortgage, there is no requirement for flood insurance, she said.

Insurance agent Margaret Chong of Equity Underwriters Insurance said she is trying to get the best possible rate through the federal programs for a Hawaii Kai client whose house, which is near a stream, formerly did not require insurance but is now partially in a high-risk flood zone.

"We understand because times are hard, and flood insurance is more expensive than homeowner’s insurance," said Chong, whose company has been checking whether its clients’ properties are affected by the map changes.

First Insurance Co. of Hawaii has seen less than a 10 percent increase in flood insurance policies, said Steve Tabussi, vice president of customer solutions.

He said it was hard to say how many of those policies were prompted by the change in flood maps.

The National Flood Insurance Program’s deadlines passed earlier for Kauai and Maui. The deadline for the Big Island has not been set.

The flood insurance rate maps, which determine whether a property is vulnerable to flooding from a 100-year storm, are separate from the state’s tsunami inundation maps, which show areas that should be evacuated in case of a tsunami.