More than 2.4 million seniors in Florida rely on Medicare, and a good chunk of them could face rising health care premiums next year.

With Medicare's annual open enrollment period beginning Sunday, most of the changes to plans and services seem slight for 2018. But experts say Floridians will be among the millions affected nationwide by anticipated rising premiums for Part B plans, which cover outpatient care, doctor bills, physical therapy and more routine health services.

Part B is optional to enroll in and costs most people a monthly premium, which was on average around $134 in 2017, depending on the enrollee's income. However, participants paid around $109 a month if they chose to have the monthly fee deducted from their Social Security checks. These are the prices that will rise in 2018, analysts say.

Cost-of-living adjustments that are expected to slightly inflate Social Security payouts next year will likely be eaten up mostly by seniors' rising Part B premiums. Experts estimate that premiums paid through Social Security will likely be around $20-$30 more a month next year.