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Costa Mesa Weather by Month
Average temperatures, rainfall and humidity for Costa Mesa, United States, month by month, built from OpenWeather's historical records. Use it to see what a typical Costa Mesa month looks like before you travel — then check the live Costa Mesa forecast for the days ahead.
Warmest month
August
29°C average high
Coolest month
January
10°C average low
Wettest month
October
93 mm of rain
Driest month
July
4 mm of rain
Average temperature and rainfall in Costa Mesa by month
Averages of the daily highs and lows recorded in each month, with total rainfall, mean humidity and mean wind speed.
| Month | Avg high | Avg low | Record low / high | Rainfall | Humidity | Wind |
|---|---|---|---|---|---|---|
| January | 20°C | 10°C | 1°C / 32°C | 54 mm | 65% | 9 km/h |
| February | 20°C | 11°C | 3°C / 32°C | 52 mm | 65% | 9 km/h |
| March | 21°C | 12°C | 5°C / 33°C | 51 mm | 70% | 10 km/h |
| April | 22°C | 13°C | 7°C / 37°C | 13 mm | 69% | 10 km/h |
| May | 22°C | 15°C | 9°C / 37°C | 14 mm | 73% | 10 km/h |
| June | 25°C | 17°C | 12°C / 42°C | 13 mm | 75% | 10 km/h |
| July | 28°C | 19°C | 15°C / 41°C | 4 mm | 75% | 10 km/h |
| August | 29°C | 19°C | 14°C / 38°C | 11 mm | 75% | 9 km/h |
| September | 28°C | 19°C | 12°C / 42°C | 8 mm | 73% | 9 km/h |
| October | 26°C | 16°C | 9°C / 39°C | 93 mm | 70% | 8 km/h |
| November | 23°C | 13°C | 4°C / 34°C | 22 mm | 63% | 8 km/h |
| December | 19°C | 10°C | 2°C / 29°C | 51 mm | 66% | 8 km/h |
Best time to visit Costa Mesa
The most comfortable time to visit Costa Mesa is generally May to June and November, balancing mild daytime temperatures against the driest stretch of the year. The city has a moderate seasonal swing and rain concentrates around October, totalling about 387 mm a year.
Travellers who prefer heat should aim for August, when highs average 29°C. October is the month to avoid if rain would spoil your plans — it averages 93 mm, roughly 21× the rainfall of July.
Source: OpenWeather historical and statistical weather data. Values are long-term averages, not a forecast — see the Costa Mesa forecast for what is happening now.