Weather in Phoenix in September

The month to avoid. September is the month most people should skip in Phoenix. Daytime highs average 38.6 °C and the afternoon is not negotiable — outdoor plans move to early morning or evening.

September ranks 12 of 12 — near the bottom of Phoenix's year. November is the month that works, and the swing between the two is 67 points, which is a different holiday rather than a slightly better one.

Rain falls on only 4 days, so an itinerary with no wet-weather fallback is a reasonable risk. Pack for heat management rather than style: shade, water, and a schedule that gives up on the middle of the day.

What the averages hide

Averages flatten a month, and this one hides a few things: 26 days of the month clear 35 °C — that is not a heatwave, it is the month. Across the twenty years measured, the hottest September day reached 46.9 °C and the coldest night fell to 14.3 °C, and the wettest single day dropped 33 mm — roughly 150% of the month's rain in one day.

This is the volatile part. September rainfall has ranged from 2 mm to 94 mm across the twenty years measured — a 92 mm spread around an average of 22 mm. The average is real but almost no individual September looks like it, so treat the figure as the middle of a wide range rather than a forecast.

Wind is light at 6.9 km/h, so the temperature on the page is close to the temperature on your skin, and the air is dry at 31% humidity, which makes the heat far more bearable than the same figure somewhere humid — and dehydrates you faster than you expect.

How September sits in the year

The month is on the way down: 2.2 °C cooler than August, with October dropping another 6.1 °C. The first week and the last are not the same trip.

Daylight in September

12.4 hours of daylight, losing 1 hours across the month. That is between Phoenix's extremes of 14.4 and 10 hours, so days are long enough not to constrain the plan.

An inland climate

With no coast nearby, the year swings a fair way — 35.6 °C between the warmest afternoons and the coldest nights, wider than any coastal city at this latitude would manage. Within September itself the daily swing is 14.5 °C, so mornings and afternoons need different clothes.

How busy it gets

Off season. The genuine off season: cheapest by a distance, with the caveat that some tours and restaurants close entirely.

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

September in Phoenix versus nearby

If Phoenix is one option among several, the nearby comparison is worth making. Sedona is a better bet in September — 7.8 °C cooler, 3 days more rain. Tucson is a better bet in September — 3.6 °C cooler, 4 days more rain.

So: September is a compromise. November is 67 points better and is what Phoenix is actually like at its best — worth moving the trip for if that is possible, and worth adjusting expectations for if it is not.

Every month in Phoenix

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