Weather in Indianapolis in September

Prime time. September is about as good as Indianapolis gets. Highs average 25.8 °C, lows 13.6 °C, and rain falls on 8 days — nothing in the month is working against you.

September is the highest-scoring month of the twelve. The nearest rival is October, and the month at the other end of the year is January.

Rain on 8 days, 3 of them heavy. Enough to need a plan B, not enough to need a plan around it. 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: 5 days top 30 °C — hot spells arrive, but they break. Across the twenty years measured, the hottest September day reached 36.5 °C and the coldest night fell to 2.7 °C, and the wettest single day dropped 68 mm — roughly 84% of the month's rain in one day.

September is moderately variable: 20 mm in the driest year against 159 mm in the wettest, around an average of 81 mm. Roughly two Septembers in three land near that average, and the third does something else entirely.

Wind is light at 8.2 km/h, so the temperature on the page is close to the temperature on your skin, and humidity is unremarkable at 72%.

How September sits in the year

The month is on the way down: 2.6 °C cooler than August, with October dropping another 7.4 °C. The first week and the last are not the same trip.

Daylight in September

12.5 hours of daylight, losing 1.3 hours across the month. That is between Indianapolis's extremes of 15 and 9.4 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.

How busy it gets

Peak season. Expect the highest prices of the year and to be booking well ahead.

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

September in Indianapolis versus nearby

If Indianapolis is one option among several, the nearby comparison is worth making. Louisville is close enough to be a coin toss — within a degree on temperature, 1 day more rain. Fort Wayne is close enough to be a coin toss — within a degree on temperature, 2 days more rain.

So: September is the answer for Indianapolis. If it is booked out or priced out, October is the next best thing at 7 points behind, and January is the month to keep off the shortlist.

Every month in Indianapolis

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