In September, Castro Valley typically sees daytime highs of 25.9°C and overnight lows around 13.0°C. Compared to the annual average high of 20.0°C, September runs +5.9°C.
September in Castro Valley averages a daytime high of 25.9°C and an overnight low of 13.0°C.
September runs +5.9°C compared to Castro Valley's annual average high of 20.0°C, ranking #1 of 12 months by warmth.
Plan for daytime highs near 25.9°C and cooler evenings around 13.0°C.