Marathon, Florida Keys weather in September
Temperature, sea and sunshine in September: long-term averages from 30 years of weather data, not a forecast.
Holiday weather in September
Good
Best time to visit: March – May, July, November – December
What is the weather like in Marathon, Florida Keys in September?
In September, Marathon, Florida Keys is hot: daytime highs average 29 °C, and even at night it stays warm at around 27 °C. The sea averages 29.6 °C – almost as warm as a bath. The sun shines for around 7 hours a day. It rains often – on about 17 days, adding up to 134 mm. The air is often humid and muggy. All in all, September is a good month for a holiday in Marathon, Florida Keys.
September compared
How the weather changes from August to October. Tap a month to open it.
| AugustAug | SeptemberSep | OctoberOct | |
|---|---|---|---|
| Score | 81 | 75 | 81 |
| Day | 29° | 29° | 27° |
| Night | 28° | 27° | 26° |
| Sea | 30° | 30° | 28° |
| Sun | 8 h | 7 h | 7 h |
| Rain days | 16 | 17 | 13 |
More details for September
- Daylight
- 12 h 20 min07:10 – 19:30
- UV index
- 10 · very highclear sky, noon (estimate)All months
- Muggy days
- 30 daysdew point 18 °C or moreAll months
- Wind
- 24 km/haverage daily peakAll months
- Cloud cover
- 63 %on averageAll months
- Hot days
- 0 days30 °C or moreAll months
- Time zone
- UTC−4America/New_York
How the score comes together
- Temperatureweight 35 %100 %
- Seaweight 25 %100 %
- Sunshineweight 20 %68 %
- Few rainy daysweight 20 %9 %
Each factor is rated from 0 to 100 % and weighted for the travel style “Sun, sea & sand”.
What to pack in September
- Swimwear
- Sunscreen
- Sunglasses & sun hat
- Light, breathable clothes
- Insect repellent
- Rain jacket or umbrella
Marathon, Florida Keys in September: quick answers
Is Marathon, Florida Keys hot in September?
Yes. In September, Marathon, Florida Keys is hot: daytime highs average 29 °C and nights stay around 27 °C.
Can you swim in Marathon, Florida Keys in September?
Yes. In September the sea averages 29.6 °C – almost as warm as a bath.
Does it rain much in Marathon, Florida Keys in September?
It rains often – on about 17 days, adding up to 134 mm.
Marathon, Florida Keys month by month
The whole year in Marathon, Florida KeysAll destinations: USAFlorida weather in SeptemberWhere to go in SeptemberSea temperature in September
Climate averages 1996–2025, not a forecast. Data: Copernicus ERA5 / ERA5-Land via Open-Meteo.com (CC BY 4.0), NOAA OISST, WMO 1991–2020 (NOAA NCEI), GeoNames (CC BY 4.0). Sources & licences