Weather in Irvine in September

Prime time. September is about as good as Irvine gets. Highs average 23.4 °C, lows 19 °C, and rain falls on 0 days — nothing in the month is working against you.

September ranks 4 of 12 in Irvine: past the worst of the year but short of June, which is the month to book if the dates are open.

Rain is not a factor worth planning around this month. Nothing specialised needed — this is the month you pack for the trip rather than for the weather.

What the averages hide

Averages flatten a month, and this one hides a few things: the day barely swings — 4.4 °C between the overnight low and the afternoon high. Across the twenty years measured, the hottest September day reached 33 °C and the coldest night fell to 15 °C, and the wettest single day dropped 26 mm — roughly 867% of the month's rain in one day.

September is dependably dry, and that reliability is the point: across the twenty years measured, the wettest September on record still only managed 31 mm, and the driest managed 0 mm. There is no meaningful variability to plan around, which makes this one of the few months anywhere that you can build a fixed outdoor itinerary against without a fallback. The wettest single day in twenty years of Septembers brought 26 mm. Rain simply is not the variable that decides this trip — heat, crowds and cost are.

Wind is light at 8.2 km/h, so the temperature on the page is close to the temperature on your skin, and humidity runs at 75%, high enough to notice on the warm days without dominating them.

How September sits in the year

Temperatures hold steady either side: 23.1 °C in August, 23.4 here, 22.2 in October. Nothing about the timing within the month matters much.

Daylight in September

12.4 hours of daylight, losing 1 hours across the month. That is between Irvine's extremes of 14.4 and 9.9 hours, so days are long enough not to constrain the plan.

An inland climate

Despite being inland, the year stays fairly even: 10.7 °C between the year's warmest afternoons and coldest nights.

How busy it gets

Peak season. Expect the highest prices of the year and to be booking well ahead. If the dates are flexible, April is the trade worth considering — 13 points weaker on weather, and materially quieter.

Crowd levels are estimated from climate desirability and school-holiday calendars, not from visitor numbers.

September in Irvine versus nearby

If Irvine is one option among several, the nearby comparison is worth making. Riverside is the weaker option in September — 12.1 °C warmer, 1 day more rain. Los Angeles is the weaker option in September — 8.5 °C warmer, the same number of rain days.

So: September is effectively as good as it gets here — 0 points behind June, which is inside the margin where the weather stops being the deciding factor and price starts being it.

Every month in Irvine

See all twelve months in Irvine, or where else to go in September.