September Weather Changes You Can Expect | Weather.com (2024)

September is typically a month of transition from summer to fall, with weather ranging from hurricanes to snow.

Here's a closer look at what changes to expect in the weather this month.

C​ooling down: High and low temperatures take a noticeable dip by the end of the month. For many, one of the clearest signs that fall is here is the cool, crisp mornings that become more common by the end of September.

Average lows in September are in the 50s and 60s for much of the Lower 48, while parts of the northern tier and the higher elevations experience average lows in the 30s and 40s. Morning lows in the 70s remain in much of Florida, along parts of the Gulf Coast and the Desert Southwest.

For example, lows start the month in the mid-60s in Boston but by Sept. 30, the average low is 53 degrees. In Denver, the average low on Sept. 1 is 55 degrees but tumbles to 44 by the end of the month.

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But some heat lingers: Average highs for the month are in the 60s and 70s across much of the northern tier, while 80s still hang on across the southern U.S., with 90s and 100s in parts of Florida, Texas and the Desert Southwest.

For instance, the average high temperature in early September in Atlanta is 87 degrees but by the end of the month, it's around 80. In Minneapolis, the average high is in the upper 70s to start the month but falls to the mid-60s by the start of October.

Shrinking daylight: The hours of sunlight decrease throughout September with the fall equinox on Sept. 22 this year. The autumnal equinox is when the sun shines directly on the equator, meaning both the Northern and Southern hemispheres receive the same amount of daylight. The amount of daylight is not exactly 12 hours on the equinox in the United States but is close in many locations.

Areas farther north see a bigger change in daylight hours during September. Locations across the northern tier lose more than an hour of daylight from the beginning of the month until the end. Anchorage, Alaska, receives almost 2 hours and 45 minutes less daylight on Sept. 30 compared to Sept. 1.

Sunrises get later throughout the month, but the earlier sunsets are more noticeable and signal, for many, that winter is coming.

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Four named storms form in the Atlantic in a typical September, with 2 to 3 of them becoming hurricanes and one of those reaching major hurricane status (Category 3 or higher on the Saffir-Simpson Hurricane Wind Scale).

The last few Septembers were very busy. Six storms formed last September. Two major hurricanes - Fiona, then Ian - occurred in September 2022. In September 2020, there were 10 named storms with four hurricanes.

Snow ... really: It may sound "too soon," but there are some areas where snow can fall in September.

It's most common in the higher elevations and in Alaska, where Fairbanks averages 2.4 inches of snow in September. Cheyenne, Wyoming, averages just under an inch of snow, although measurable snow doesn't fall every September.

Snow has also fallen in parts of the Plains, Great Lakes and northern New England in September. Mount Washington, New Hampshire, averages 1.2 inches of snowfall in September.

In early September 2020​, one of the earliest Front Range snowstorms on record dumped snow from Montana to New Mexico.

The previous September, a historic snowstorm smashed September records in the Northern Rockies, dumping up to 4 feet of snow.

Monsoon to Santa Ana: One western pattern change is the return of Santa Ana winds. Strong high pressure over the interior West results in an offshore pattern with wind flowing from the higher elevations of the desert areas through canyons and passes in Southern California. Wind speeds increase as they are funneled through the mountain passes. Hot temperatures often accompany Santa Ana winds.

The combination of low humidity and strong winds can add to the fire danger, especially in early fall as California ends its dry season.

Meanwhile, the Southwest monsoon season comes to an end by late September. This is also due to a shifting of the wind and temperature patterns in the region.

In summer, the winds flow from the ocean into the Southwest, resulting in wet weather over the region. During the fall, that changes as the wind flows from the land to the ocean, since the land begins to cool and the water is warmer.

Linda Lam is a lead meteorologist at weather.com and began her career in 2006 at The Weather Company (formerly WSI).