(MONEY Magazine) – Coastal dwellers take note: Before the 2000 hurricane season ends in November, climatologists are predicting that 11 tropical storms will form in the Atlantic, seven of which may become hurricanes. If your home is damaged as a result, you may face higher out-of-pocket expenses than you expected. The reason: In recent years, insurance companies have been replacing flat-dollar deductibles with percentage-based ones for damage caused by hurricanes and certain other windstorms. (Most flood damage caused by hurricanes is covered by a separate flood insurance policy from the federal government.)

Typically, a homeowners policy carries a flat deductible, which ranges from $250 to $1,000, depending on your premium. Now, in at least 15 coastal states stretching from Maine to Texas, your deductible for wind-related storm damage may equal 2% to 5% of your home's insured value, which means that if you have a $200,000 policy, you'd have to cover as much as $10,000 in hurricane-related damage before your homeowners insurance kicks in.

In some areas, these percentage deductibles are mandatory on new policies and renewals. In others, you may be able to pay a higher premium to lower the percent or, in some cases, keep a flat dollar deductible. If so, you should do it, says Ray Julian, a Newton, Mass. certified financial planner. It may not even be that expensive. For example, a homeowner in Orange County, Fla. with a $130,000 policy from Hartford would pay only $29 more a year to cut the percentage deductible from 5% to 2% ($6,500 to $2,600).

Finally, homeowners who live in high-risk coastal areas could take yet another financial hit. The Federal Emergency Management Agency--which administers the National Flood Insurance Program--just released a study that proposes, among other measures, that Congress impose a surcharge on flood insurance in high-risk coastal regions, such as barrier islands and flood plains. This could double flood-insurance rates--which currently average about $350 for up to $250,000 of coverage--in the most hazardous areas.

--ROBERTA KIRWAN