Hyannis, Cape Cod 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
Fair
Best time to visit: July – August
What is the weather like in Hyannis, Cape Cod in September?
In September, Hyannis, Cape Cod is mild: daytime highs average 20 °C, and nights cool down to about 17 °C. The sea averages 19.3 °C – bracing, so a wetsuit helps for longer swims. Expect around 6 hours of sunshine a day. Rain falls on about 9 days, adding up to 94 mm. All in all, September is a so-so month for a holiday in Hyannis, Cape Cod.
September compared
How the weather changes from August to October. Tap a month to open it.
| AugustAug | SeptemberSep | OctoberOct | |
|---|---|---|---|
| Score | 66 | 40 | 20 |
| Day | 23° | 20° | 16° |
| Night | 20° | 17° | 12° |
| Sea | 21° | 19° | 15° |
| Sun | 8 h | 6 h | 5 h |
| Rain days | 9 | 9 | 9 |
More details for September
- Daylight
- 12 h 33 min06:20 – 18:53
- UV index
- 6 · highclear sky, noon (estimate)All months
- Muggy days
- 6 daysdew point 18 °C or moreAll months
- Wind
- 23 km/haverage daily peakAll months
- Cloud cover
- 53 %on averageAll months
- Hot days
- 0 days30 °C or moreAll months
- Snow days
- 0 days1 cm or more of fresh snowAll months
- Time zone
- UTC−4America/New_York
How the score comes together
- Temperatureweight 35 %20 %
- Seaweight 25 %33 %
- Sunshineweight 20 %57 %
- Few rainy daysweight 20 %68 %
Each factor is rated from 0 to 100 % and weighted for the travel style “Sun, sea & sand”.
What to pack in September
- Wetsuit for longer swims
- Sunscreen
- Rain jacket or umbrella
Hyannis, Cape Cod in September: quick answers
Is Hyannis, Cape Cod hot in September?
No. In September, Hyannis, Cape Cod is mild: daytime highs average 20 °C and nights drop to about 17 °C.
Can you swim in Hyannis, Cape Cod in September?
Only if you don't mind cold water: in September the sea averages just 19.3 °C. Comfortable swimming is possible in August.
Does it rain much in Hyannis, Cape Cod in September?
Rain falls on about 9 days, adding up to 94 mm.
Hyannis, Cape Cod month by month
The whole year in Hyannis, Cape CodAll destinations: USAWhere 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