In December, Costa Mesa typically sees daytime highs of 19.2°C and overnight lows around 8.0°C. Compared to the annual average high of 22.1°C, December runs -2.9°C.
December in Costa Mesa averages a daytime high of 19.2°C and an overnight low of 8.0°C.
December runs -2.9°C compared to Costa Mesa's annual average high of 22.1°C, ranking #10 of 12 months by warmth.
Plan for daytime highs near 19.2°C and cooler evenings around 8.0°C.