September Weather in Brest France

Daily high temperatures decrease by 4°F, from 68°F to 63°F, rarely falling below 58°F or exceeding 75°F.

Daily low temperatures decrease by 3°F, from 56°F to 52°F, rarely falling below 46°F or exceeding 61°F.

For reference, on August 2, the hottest day of the year, temperatures in Brest typically range from 57°F to 69°F, while on February 7, the coldest day of the year, they range from 40°F to 49°F.

The figure below shows you a compact characterization of the hourly average temperatures for the quarter of the year centered on September. The horizontal axis is the day, the vertical axis is the hour of the day, and the color is the average temperature for that hour and day.

Lincoln City, Oregon, United States (5,031 miles away) and Scottsdale, Tasmania, Australia (10,997 miles) are the far-away foreign places with temperatures most similar to Brest (view comparison).

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The month of September in Brest experiences gradually increasing cloud cover, with the percentage of time that the sky is overcast or mostly cloudy increasing from 44% to 49%.

The clearest day of the month is September 1, with clear, mostly clear, or partly cloudy conditions 56% of the time.

For reference, on January 3, the cloudiest day of the year, the chance of overcast or mostly cloudy conditions is 66%, while on July 24, the clearest day of the year, the chance of clear, mostly clear, or partly cloudy skies is 61%.

A wet day is one with at least 0.04 inches of liquid or liquid-equivalent precipitation. In Brest, the chance of a wet day over the course of September is very rapidly increasing, starting the month at 20% and ending it at 29%.

For reference, the year's highest daily chance of a wet day is 42% on December 31, and its lowest chance is 16% on August 1.

Rainfall

To show variation within the month and not just the monthly total, we show the rainfall accumulated over a sliding 31-day period centered around each day.

The average sliding 31-day rainfall during September in Brest is increasing, starting the month at 1.4 inches, when it rarely exceeds 3.3 inches or falls below 0.2 inches, and ending the month at 2.3 inches, when it rarely exceeds 4.5 inches or falls below 0.7 inches.

Over the course of September in Brest, the length of the day is rapidly decreasing. From the start to the end of the month, the length of the day decreases by 1 hour, 41 minutes, implying an average daily decrease of 3 minutes, 29 seconds, and weekly decrease of 24 minutes, 22 seconds.

The shortest day of the month is September 30, with 11 hours, 44 minutes of daylight and the longest day is September 1, with 13 hours, 24 minutes of daylight.

The earliest sunrise of the month in Brest is 7:35 AM on September 1 and the latest sunrise is 40 minutes later at 8:15 AM on September 30.

The latest sunset is 8:59 PM on September 1 and the earliest sunset is 1 hour, 0 minutes earlier at 7:59 PM on September 30.

Daylight saving time is observed in Brest during 2026, but it neither starts nor ends during September, so the entire month is in daylight saving time.

For reference, on June 21, the longest day of the year, the Sun rises at 6:16 AM and sets 16 hours, 7 minutes later, at 10:23 PM, while on December 21, the shortest day of the year, it rises at 9:06 AM and sets 8 hours, 19 minutes later, at 5:25 PM.

The figure below presents a compact representation of the sun's elevation (the angle of the sun above the horizon) and azimuth (its compass bearing) for every hour of every day in the reporting period. The horizontal axis is the day of the year and the vertical axis is the hour of the day. For a given day and hour of that day, the background color indicates the azimuth of the sun at that moment. The black isolines are contours of constant solar elevation.

The figure below presents a compact representation of key lunar data for September 2026. The horizontal axis is the day, the vertical axis is the hour of the day, and the colored areas indicate when the moon is above the horizon. The vertical gray bars (new Moons) and blue bars (full Moons) indicate key Moon phases. The label associated with each bar indicates the date and time that the phase is obtained, and the companion time labels indicate the rise and set times of the Moon for the nearest time interval in which the moon is above the horizon.

We base the humidity comfort level on the dew point, as it determines whether perspiration will evaporate from the skin, thereby cooling the body. Lower dew points feel drier and higher dew points feel more humid. Unlike temperature, which typically varies significantly between night and day, dew point tends to change more slowly, so while the temperature may drop at night, a muggy day is typically followed by a muggy night.

The chance that a given day will be muggy in Brest is essentially constant during September, remaining within 1% of 1% throughout.

For reference, on August 11, the muggiest day of the year, there are muggy conditions 2% of the time, while on October 23, the least muggy day of the year, there are muggy conditions 0% of the time.

This section discusses the wide-area hourly average wind vector (speed and direction) at 10 meters above the ground. The wind experienced at any given location is highly dependent on local topography and other factors, and instantaneous wind speed and direction vary more widely than hourly averages.

The average hourly wind speed in Brest is increasing during September, increasing from 11.8 miles per hour to 12.9 miles per hour over the course of the month.

For reference, on January 1, the windiest day of the year, the daily average wind speed is 17.1 miles per hour, while on August 5, the calmest day of the year, the daily average wind speed is 10.9 miles per hour.

The hourly average wind direction in Brest throughout September is predominantly from the west, with a peak proportion of 38% on September 1.

Brest is located near a large body of water (e.g., ocean, sea, or large lake). This section reports on the wide-area average surface temperature of that water.

The average surface water temperature in Brest is essentially constant during September, remaining within 1°F of 60°F throughout.

Definitions of the growing season vary throughout the world, but for the purposes of this report, we define it as the longest continuous period of non-freezing temperatures (≥ 32°F) in the year (the calendar year in the Northern Hemisphere, or from July 1 until June 30 in the Southern Hemisphere).

The growing season in Brest typically lasts for 10 months (303 days), from around February 17 to around December 16, rarely starting after March 19, or ending before November 20.

The month of September in Brest is reliably fully within the growing season.

Growing degree days are a measure of yearly heat accumulation used to predict plant and animal development, and defined as the integral of warmth above a base temperature, discarding any excess above a maximum temperature. In this report, we use a base of 50°F and a cap of 86°F.

The average accumulated growing degree days in Brest are increasing during September, increasing by 282°F, from 1,346°F to 1,628°F, over the course of the month.

This section discusses the total daily incident shortwave solar energy reaching the surface of the ground over a wide area, taking full account of seasonal variations in the length of the day, the elevation of the Sun above the horizon, and absorption by clouds and other atmospheric constituents. Shortwave radiation includes visible light and ultraviolet radiation.

The average daily incident shortwave solar energy in Brest is rapidly decreasing during September, falling by 1.6 kWh, from 5.0 kWh to 3.4 kWh, over the course of the month.

For the purposes of this report, the geographical coordinates of Brest are 48.400 deg latitude, -4.483 deg longitude, and 194 ft elevation.

The topography within 2 miles of Brest contains only modest variations in elevation, with a maximum elevation change of 384 feet and an average elevation above sea level of 164 feet. Within 10 miles contains only modest variations in elevation (561 feet). Within 50 miles contains significant variations in elevation (1,273 feet).

The area within 2 miles of Brest is covered by artificial surfaces (84%), within 10 miles by cropland (50%) and water (23%), and within 50 miles by water (64%) and cropland (25%).