Weather in Hermosillo in September

A hard month. September asks something of you. Go in knowing what. Daytime highs average 36.3 °C and the afternoon is not negotiable — outdoor plans move to early morning or evening.

September ranks 9 of 12 in Hermosillo: past the worst of the year but short of December, which is the month to book if the dates are open.

Rain on 9 days, 2 of them heavy. Enough to need a plan B, not enough to need a plan around it. 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: 20 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 45 °C and the coldest night fell to 15.8 °C, and the wettest single day dropped 62 mm — roughly 78% of the month's rain in one day.

September is moderately variable: 16 mm in the driest year against 163 mm in the wettest, around an average of 79 mm. Roughly two Septembers in three land near that average, and the third does something else entirely.

Wind is light at 7.3 km/h, so the temperature on the page is close to the temperature on your skin, and humidity is unremarkable at 58%.

How September sits in the year

Temperatures hold steady either side: 36.8 °C in August, 36.3 here, 33.5 in October. Nothing about the timing within the month matters much. Rain is the thing that moves: October brings 7 days less of it, so pushing the dates later buys drier weather.

Daylight in September

12.4 hours of daylight, losing 0.9 hours across the month. That is between Hermosillo's extremes of 14 and 10.3 hours, so days are long enough not to constrain the plan.

An inland climate

With no coast nearby, the year swings a fair way — 30.1 °C between the warmest afternoons and the coldest nights, wider than any coastal city at this latitude would manage.

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 Hermosillo versus nearby

If Hermosillo is one option among several, the nearby comparison is worth making. Tucson is close enough to be a coin toss — within a degree on temperature, 1 day less rain. Chihuahua is a better bet in September — 7 °C cooler, 2 days more rain.

So: September is a compromise. December is 57 points better and is what Hermosillo 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 Hermosillo

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