NOAA's tide gauge at Fort Myers, the closest long record to Charlotte Harbor, shows relative sea level rising about 1.43 inches per decade since 1965, or roughly 8 to 9 inches over six decades. Gauges at Naples and St. Petersburg show similar trends. That is a measured history; projections of future rise are a separate question, and NOAA's 2022 report expects the pace along the Gulf coast to be faster in the coming decades than in the past century.
What the nearby tide gauges show
A tide gauge measures water height against a benchmark on land, so its trend is "relative": it includes both the change in the water and any sinking or rising of the ground at the station. NOAA calculates the trend from monthly averages, which smooths out tides, storms and seasons.
| NOAA station | Years of record | Trend (inches per decade) | Approximate change over the record |
|---|---|---|---|
| Fort Myers (8725520) | 1965 to 2025 | 1.43 (plus or minus 0.08) | About 8 to 9 inches |
| Naples (8725110) | 1965 to 2023 | 1.32 (plus or minus 0.08) | About 7 to 8 inches |
| St. Petersburg (8726520) | 1947 to 2025 | 1.23 (plus or minus 0.05) | About 9 to 10 inches |
Source: NOAA Center for Operational Oceanographic Products and Services, relative sea level trends with data through December 2025 (Naples through 2023). The right-hand column multiplies each trend by the length of its record and rounds; it is a summary of the trend, not a difference between two individual readings. The three records cover different years, so compare them with care. The latest numbers are on NOAA's sea level trends page.
Water at these gauges also runs higher in late summer and fall than in winter as part of a normal seasonal cycle. That is why the highest "king tides" of the year tend to arrive in the fall.
A trend is not a projection
A trend describes what has already been measured. A projection estimates what may happen next, using physics and assumptions about warming oceans and melting ice. Drawing a straight line forward from the gauge record is not a projection, and it may understate future change if the rate keeps increasing.
NOAA's 2022 interagency Sea Level Rise Technical Report projects that sea level along U.S. coastlines will rise on average about 10 to 12 inches between 2020 and 2050, with the Gulf coast among the regions expecting the most, about 14 to 18 inches by 2050. The same report expects moderate high-tide flooding, the kind that typically disrupts traffic and damages property, to occur on average more than 10 times as often nationally by 2050 as it does today.
These are regional averages, not predictions for a particular street. Local flooding also depends on ground elevation, drainage, seawall heights, wind and tide.
How higher water shows up before a storm
Rising seas are noticed first on calm days. The highest tides of the year reach low streets, boat ramps and the tops of seawalls that used to stay dry, a pattern often called sunny-day or nuisance flooding.
Drainage changes next. Many storm drains empty into canals and tidal creeks, and when the water in them stands higher, rain has less downhill fall to escape. Streets can flood from an ordinary afternoon shower at high tide, or salt water can push backward up the drain pipes.
Storm surge then starts from a higher base. The same surge reaches farther inland when the sea is a few inches higher to begin with, although each storm's track, size and timing still matter most. Surge itself is explained in more detail on the hurricanes page.
What it means for the estuary's habitats
Mangroves and salt marsh. Mangroves are spreading north and landward in Florida as hard freezes become less frequent and water rises. Along this coast they can move into salt marsh and bare salt flats that sit slightly higher on the shore. Where seawalls, roads or fill block that movement, marsh and mangroves get squeezed between deeper water and land they cannot occupy.
Seagrass. Seagrass grows only as deep as light reaches. As water deepens over a bed, less light gets to the leaves, especially in the tea-colored upper harbor; new shallow areas may open up at the landward edge if the bottom is suitable. The seagrass and mangrove guide describes what keeps grass beds healthy.
Tidal rivers and groundwater. Salt water can push farther up the tidal Peace and Myakka and into shallow aquifers and coastal freshwater wetlands. River flow still controls where the salt line sits from season to season, as described on the rivers and salinity page, but the starting point is shifting.
What local planning documents consider
Florida's Resilient Florida program, created in 2021 (section 380.093, Florida Statutes), funds vulnerability assessments by counties and cities. FDEP's compliance checklist requires at least two sea level rise scenarios; for assessments started after July 1, 2024, those must include NOAA's 2022 intermediate-low and intermediate projections, with planning horizons that include 2040 and 2070. The assessments overlay those scenarios on local elevations, roads, utilities and critical facilities to show where planning attention is needed. Program details are on FDEP's Resilient Florida page, and the counties and cities around the harbor post their own assessments on their websites.
How to read the data yourself
- Start with Fort Myers. Open NOAA's trends page, find the station and look at the long-term graph of monthly means.
- Check the dates. Note when the record starts and ends, not just when the page was updated.
- Keep units straight. A rate (inches per decade) is not the same as a total change.
- Match the scenario. In a local assessment, check which projection and which year each map shows.
- Read the map notes. See whether rainfall, surge or drainage are included or left out.
- Treat a flooded road as a clue. It may come from tide, rain, a blocked drain or all three.
Frequently Asked Questions
How much has sea level risen near Charlotte Harbor?
NOAA's Fort Myers gauge shows a relative rise of about 1.43 inches per decade from 1965 through 2025, which adds up to roughly 8 to 9 inches. Naples and St. Petersburg show similar trends.
Does rising sea level mean every high tide is higher than the last?
No. Tides, wind, seasons and river flow make water levels go up and down constantly. The trend describes the slow change underneath all that variation.
Can the Fort Myers gauge tell me whether my home will flood?
No. The gauge describes the regional water level. Flood risk for a particular property depends on its ground elevation, drainage and the storm or tide in question, which local flood maps and assessments address.
Why do local plans show several different future water levels?
Planners use more than one scenario because the future rate of rise is uncertain. Each map should state which projection and which year it shows; check those labels before comparing maps.