In September, Costa Mesa typically sees daytime highs of 26.2°C and overnight lows around 15.9°C. Compared to the annual average high of 22.1°C, September runs +4.2°C.
September in Costa Mesa averages a daytime high of 26.2°C and an overnight low of 15.9°C.
September runs +4.2°C compared to Costa Mesa's annual average high of 22.1°C, ranking #2 of 12 months by warmth.
Plan for daytime highs near 26.2°C and cooler evenings around 15.9°C.