Port Jefferson — Water Temperature in September
Water Temperature Range
18°C
minimum
22°C
average
25°C
maximum
Water Temperature Chart for Month
The chart shows the average daily water temperature for each day of the month based on historical data.
Table of Water Temperatures by Day of the Month for Previous Years
| Day | 2025 | 2024 | 2023 | 2022 |
|---|---|---|---|---|
| SEP 1 | 23°C | 22°C | 24°C | 23°C |
| SEP 2 | 22°C | 21°C | 23°C | 23°C |
| SEP 3 | 23°C | 22°C | 24°C | 23°C |
| SEP 4 | 22°C | 22°C | 22°C | 22°C |
| SEP 5 | 22°C | 20°C | 22°C | 23°C |
| SEP 6 | 22°C | 21°C | 22°C | 23°C |
| SEP 7 | 22°C | 21°C | 23°C | 24°C |
| SEP 8 | 22°C | 22°C | 23°C | 23°C |
| SEP 9 | 22°C | 21°C | 22°C | 23°C |
| SEP 10 | 22°C | 21°C | 23°C | 23°C |
| SEP 11 | 22°C | 20°C | 24°C | 23°C |
| SEP 12 | 22°C | 21°C | 22°C | 23°C |
| SEP 13 | 22°C | 21°C | 23°C | 22°C |
| SEP 14 | 22°C | 21°C | 23°C | 22°C |
| SEP 15 | 22°C | 20°C | 23°C | 23°C |
| SEP 16 | 22°C | 21°C | 24°C | 22°C |
| SEP 17 | 22°C | 20°C | 23°C | 22°C |
| SEP 18 | 22°C | 21°C | 23°C | 22°C |
| SEP 19 | 22°C | 20°C | 24°C | 21°C |
| SEP 20 | 22°C | 21°C | 23°C | 21°C |
| SEP 21 | 21°C | 20°C | 23°C | 21°C |
| SEP 22 | 22°C | 21°C | 24°C | 20°C |
| SEP 23 | 21°C | 21°C | 23°C | 20°C |
| SEP 24 | 21°C | 20°C | 24°C | 19°C |
| SEP 25 | 21°C | 20°C | 23°C | 19°C |
| SEP 26 | 21°C | 20°C | 24°C | 20°C |
| SEP 27 | 21°C | 20°C | 23°C | 19°C |
| SEP 28 | 21°C | 20°C | 23°C | 19°C |
| SEP 29 | 21°C | 20°C | 23°C | 20°C |
| SEP 30 | 21°C | 20°C | 22°C | 20°C |
September: Climate and Swimming Opportunities
Average Night Air Temperature
14°C
Average Day Air Temperature
24°C
Precipitation Amount per Month
98 mm
Number of Rainy Days
9
Daylight per Day
12 hrs
Sunshine per Day
7 hrs
Average Wind Speed
14 km/h
Average Humidity
75%
With such a ratio between the average monthly temperatures of water and air, swimming feels warm and comfortable even if the day isn’t hot. The water can feel warmer than the air, so getting out may feel a bit cool.