Key West water temperature by month: a station-based seasonal analysis

A named station, with a defined historical window

This analysis uses water-temperature observations from NOAA CO-OPS station 8724580, Key West. We examined the coverage-qualified monthly summaries for the site’s 2021–2025 target period. This is a recent station baseline, rather than a 30-year climate normal or a forecast for a trip. The results are a dated snapshot reviewed on October 23, 2026.

The target period and the years actually contributing to a result are different things. Most Key West months qualify in 2023, 2024 and 2025. August also qualifies in 2021. Data gaps prevent January from meeting the publication threshold. Reporting those differences is essential: a table labeled only “five-year average” would imply equal support that this record does not have.

Monthly averages, ranges and contributing years

The mean pools the available hourly values in qualifying station-month-years. The 10th–90th percentile band describes roughly the central 80% of those historical hourly readings. It is not a confidence interval around the mean, an observed minimum-to-maximum range, or a guarantee about a future visit. NOAA’s CO-OPS API documentation identifies the water_temperature product, metric units, hourly interval and GMT time option needed to retrieve the underlying series.

All twelve months appear below so the absent January result cannot be mistaken for zero or an accidentally omitted row. A station-month-year needs at least 70% of its expected hourly readings, and a calendar month needs at least three such years. These are this site’s publication rules; NOAA supplies the observations, not these editorial coverage thresholds.

Source: Water Temperature Live analysis of NOAA CO-OPS hourly observations. UTC calendar months. Percentiles and means pool qualifying hourly values. Display values are rounded after unit conversion. January fails the minimum coverage requirement; no value has been estimated.

What the seasonal pattern supports

July’s mean is 31.869°C to three decimals. August averages 31.594°C and September 30.992°C, so the warmest part of this published record extends beyond one isolated month. The July middle band, 87.4–91.4°F (30.8–33.0°C), is narrower than October’s 79.3–86.7°F (26.3–30.4°C). Each interval blends within-month and between-year variation; it does not separate the two.

December has the lowest mean among the eleven published months: 74.1°F (23.4°C). The July-to-December mean difference is about 15.3°F (8.5°C). Because January is missing, that comparison cannot establish the full annual seasonal range or identify the coldest month of the complete year. February’s mean of 74.7°F (23.7°C) should likewise be read as a February result, without filling the neighboring gap by interpolation.

April averages 80.0°F (26.7°C), while October averages 83.2°F (28.4°C). That 3.2°F (1.8°C) difference is a useful descriptive comparison for this station record. Establishing how solar heating, weather, currents or mixing contributed would require a heat-budget analysis and additional measurements. The monthly table alone does not attribute the difference to a specific mechanism.

Why a station average is not a reef temperature

A shore station samples a particular place and instrument setting. Using its number for an offshore reef requires evidence about depth, exchange and local variability that this table does not provide. A daily satellite analysis and an in-water sensor may also represent different times and parts of the water column. Compare their definitions before treating a difference as an error.

Temperature matters ecologically, but a station monthly mean is not a coral-impact assessment. NOAA explains that sustained stress can disrupt the relationship between corals and their symbiotic algae; bleaching and mortality are distinct outcomes. The National Ocean Service’s bleaching explainer also documents cold-related bleaching in the Florida Keys, showing why “warmer is always better” would be an unsuitable ecological reading of the table.

For reef heat stress, use a product designed for that question. NOAA Coral Reef Watch’s Degree Heating Week methodology combines heat intensity and duration over a twelve-week window. We have not calculated that metric here, and the station’s monthly percentiles should not be substituted for it. No current reef alert is being announced in this article.

How to use the table with current conditions

Begin with the month to understand the recent historical background, then open the Key West observation page and check its actual timestamp and source status. A current value can differ from the monthly mean without being faulty. It can also fall outside the historical middle band: by construction, that band excludes the cooler and warmer tails of the sampled distribution.

Keep the live observation, the historical table and the planned activity separate. A monthly average does not specify conditions at a chosen beach or hour, and it does not establish swimming suitability, visibility, currents or water quality. The table helps frame a temperature question; current local information is needed to answer the rest.