United States: where to swim in September?
United States, in September: the sea is at 23.0 °C on average along the coast, from 14.5 °C to 29.4 °C depending on the spot. Where the water is warmest (29.4 °C), it is very warm. Almost lukewarm: you can get in without any cold shock.
Sea temperature, month by month
| Month | Average temperature | Depending on the spot | Where it is warmest |
|---|---|---|---|
| January | 14.4 °C | 7.1 °C – 22.1 °C | pleasant |
| February | 13.8 °C | 5.4 °C – 21.7 °C | pleasant |
| March | 14.5 °C | 5.6 °C – 22.4 °C | pleasant |
| April | 16.1 °C | 7.5 °C – 24.2 °C | warm |
| May | 18.5 °C | 11.0 °C – 26.0 °C | warm |
| June | 21.2 °C | 12.5 °C – 28.8 °C | very warm |
| July | 23.2 °C | 13.8 °C – 29.9 °C | very warm |
| August | 23.8 °C | 14.7 °C – 30.4 °C | very warm |
| September | 23.0 °C | 14.5 °C – 29.4 °C | very warm |
| October | 21.2 °C | 13.5 °C – 28.2 °C | very warm |
| November | 18.2 °C | 11.5 °C – 25.6 °C | warm |
| December | 16.1 °C | 9.2 °C – 23.7 °C | warm |
Compared with August, the water cools down by 0.8 °C in September. The warmest month: August (23.8 °C). The coldest: February (13.8 °C).
Where the water is warmest in September
- Florida 29.3 °C · very warm
- Texas 29.3 °C · very warm
- Alabama 28.9 °C · very warm
- Louisiana 28.9 °C · very warm
- Georgia 28.2 °C · very warm
- South Carolina 27.7 °C · very warm
- Hawaii 27.2 °C · very warm
- North Carolina 27.0 °C · very warm
- Virginia 24.2 °C · warm
- Maryland 23.9 °C · warm
- New Jersey 22.7 °C · warm
- New York 21.5 °C · pleasant
- Massachusetts 19.0 °C · pleasant
- California 17.0 °C · pleasant
- Maine 15.5 °C · cool
- Washington 14.4 °C · cool
- Oregon 14.1 °C · cool
- Alaska 9.1 °C · cold
And right now?
For the temperature measured right now, station by station and to the hour: United States: water temperature
Frequently asked questions
What is the sea temperature in September?
United States, in September: 23.0 °C on average along the coast, from 14.5 °C in the coolest waters to 29.4 °C in the warmest (average of the years 2011 to 2025).
Can you swim in September?
Where the water is warmest (29.4 °C), it is very warm. Almost lukewarm: you can get in without any cold shock.
What is the best month for swimming?
The water is warmest in August (23.8 °C on average) and coldest in February (13.8 °C). Where the water is warmest, it goes above 20 °C in these months: January, February, March, April, May, June, July, August, September, October, November, December.
Where is the water warmest in September?
The warmest in September: Florida (29.3 °C), Texas (29.3 °C), Alabama (28.9 °C). The coolest: Alaska (9.1 °C).
Where do these temperatures come from?
These are averages of the sea surface temperature from 2011 to 2025, computed from NOAA satellite images (OISST, one value about every 50 km), in a 100 km strip along the coasts of the main country: distant territories (overseas, remote islands) are not counted. It is an estimate, not a measurement taken at the beach: lakes and rivers are not included.