San Mateo — Water Temperature in September

Water Temperature Range

12°C

minimum

15°C

average

19°C

maximum

Get instant access to real-time water temperatures for this and all other locations with our iOS and Android apps.

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	15°C	15°C	17°C	15°C
SEP 2	15°C	15°C	18°C	13°C
SEP 3	14°C	14°C	17°C	12°C
SEP 4	15°C	15°C	17°C	15°C
SEP 5	14°C	15°C	17°C	12°C
SEP 6	16°C	15°C	17°C	15°C
SEP 7	15°C	14°C	18°C	14°C
SEP 8	15°C	15°C	17°C	14°C
SEP 9	15°C	15°C	17°C	13°C
SEP 10	14°C	16°C	16°C	12°C
SEP 11	15°C	15°C	16°C	13°C
SEP 12	15°C	16°C	17°C	14°C
SEP 13	15°C	16°C	17°C	13°C
SEP 14	15°C	16°C	17°C	13°C
SEP 15	15°C	15°C	17°C	15°C
SEP 16	14°C	15°C	16°C	12°C
SEP 17	15°C	16°C	16°C	13°C
SEP 18	15°C	17°C	16°C	15°C
SEP 19	16°C	17°C	17°C	15°C
SEP 20	16°C	16°C	18°C	15°C
SEP 21	14°C	16°C	17°C	12°C
SEP 22	15°C	16°C	17°C	14°C
SEP 23	15°C	16°C	18°C	12°C
SEP 24	16°C	17°C	18°C	14°C
SEP 25	15°C	17°C	18°C	13°C
SEP 26	15°C	15°C	18°C	14°C
SEP 27	16°C	16°C	18°C	13°C
SEP 28	15°C	16°C	18°C	14°C
SEP 29	15°C	16°C	17°C	13°C
SEP 30	16°C	16°C	18°C	14°C

September: Climate and Swimming Opportunities

Average Night Air Temperature

14°C

Average Day Air Temperature

23°C

Precipitation Amount per Month

6 mm

Number of Rainy Days

Daylight per Day

12 hrs

Sunshine per Day

9 hrs

Average Wind Speed

13 km/h

Average Humidity

70%

With such a ratio between the average monthly temperatures of water and air, swimming feels very cold and is only for cold-water enthusiasts. Most people will prefer just a brief splash, because warming up afterward can take time.