In September, Fullerton typically sees daytime highs of 29.3°C and overnight lows around 15.9°C. Compared to the annual average high of 23.9°C, September runs +5.4°C.
September in Fullerton averages a daytime high of 29.3°C and an overnight low of 15.9°C.
September runs +5.4°C compared to Fullerton's annual average high of 23.9°C, ranking #3 of 12 months by warmth.
Plan for daytime highs near 29.3°C and cooler evenings around 15.9°C.