Hottest (avg)
#1 / 12
The warmest month of the year.
September in context
How it compares to the rest of the year in San Francisco.
Wettest (avg)
#10 / 12
One of the drier months.
Daylight Hours
#6 / 12
Around the yearly average.
Windiest (avg)
#8 / 12
Close to the yearly wind average.
Highest UV
#6 / 12
Near the middle of the yearly UV range.
Most Humid
#8 / 12
Humidity stays close to the yearly norm.
Monthly climate breakdown
A detailed look at the typical climate conditions for September.
Thermal profile
Temperature
Typical daytime high
- Nighttime low
-
- Feels like (avg)
-
Light window
Sunshine
12.4 h
Average daylight
- UV index (max)
- 7
- Typical sun hours
- 05:51 - 18:16
Wet-day pattern
Rain & Snow
Typical rainfall
- Rainy days
- 1 days
- Cloud cover (avg)
- 36%
Air feel
Humidity & Wind
76%
Average humidity
- Wind (avg)
-
- Wind (max gusts)
-
Historical daily baseline
Daily climate explorer
Pick a day to inspect the usual conditions through September in San Francisco. Based on a 30-year historical climate baseline, not a forecast.
Primary control
Select a day
Scroll to compare daily conditions. The summary updates with your selection.
Secondary context
Monthly trend
Median daytime highs across the month, with a softer low line.
Median temperatureMedian lowTypical range
Day 15 selected for September. Temperature 19.7°C.
Historical disruption baseline
Typical disruptions in September
Based on 30 years of historical data, these are the disruption patterns most likely to affect plans in September.
Heat Moderate
Hot days Measures: Hot days (>=30C). Observed about 4% of days (1.2 days/month) in September. Historical risk signal only, not a day-by-day forecast.
Likely frequency
1.2 days / month
- Share of days
- ~4% of days
- Upper edge
- Up to ~36°C (P95)
Why this matters
Hot days are possible on ~1 days. Midday activity often needs adjustment around shade, hydration, and indoor fallback options.
Show all disruptions (12 more)
Wind High impact
Strong gusts Measures: Strong gust days (>=60 km/h). Observed about 1% of days (0.4 days/month) in September. Historical risk signal only, not a day-by-day forecast.
Likely frequency
0.4 days / month
- Share of days
- ~1% of days
- Upper edge
- Up to ~73km/h (P95)
Why this matters
Strong gusts are possible on ~0 days. Exposed activities and transport links are more likely to be disrupted, so keep sheltered alternatives ready.
Heat Moderate
Hot feels-like days Measures: Hot feels-like days (>=32C). Observed about 1% of days (0.4 days/month) in September. Historical risk signal only, not a day-by-day forecast.
Likely frequency
0.4 days / month
- Share of days
- ~1% of days
- Upper edge
- Up to ~38°C (P95)
Why this matters
Feels-like heat >=32C is possible on ~0 days. Midday activity often needs adjustment around shade, hydration, and indoor fallback options.
Wind Minor
Gusty days Measures: Gusty days (>=40 km/h). Observed about 38% of days (11.5 days/month) in September. Historical risk signal only, not a day-by-day forecast.
Likely frequency
11.5 days / month
- Share of days
- ~38% of days
- Upper edge
- Up to ~58km/h (P95)
Why this matters
Gusty conditions are possible on ~11 days. Exposed activities and transport links are more likely to be disrupted, so keep sheltered alternatives ready.
Humidity Minor
High humidity Measures: High humidity days (RH >=80%). Observed about 38% of days (11.3 days/month) in September. Historical risk signal only, not a day-by-day forecast.
Likely frequency
11.3 days / month
- Share of days
- ~38% of days
- Upper edge
- Up to ~87% (P95)
Why this matters
High humidity is possible on ~11 days. Comfort and pace can drop quickly, so plan shorter outdoor blocks with air-conditioned backup stops.
Cloud Minor
Cloudy days Measures: Cloudy days (cloud cover >=60%). Observed about 17% of days (5.0 days/month) in September. Historical risk signal only, not a day-by-day forecast.
Likely frequency
5.0 days / month
- Share of days
- ~17% of days
- Upper edge
- Up to ~94% (P95)
Why this matters
Cloudy skies are possible on ~5 days. Fixed-time outdoor plans are safer with a backup option and flexible timing.
Rain Minor
Wet days Measures: Wet days (>=0.1mm). Observed about 6% of days (1.9 days/month) in September. Historical risk signal only, not a day-by-day forecast.
Likely frequency
1.9 days / month
- Share of days
- ~6% of days
- Upper edge
- Up to ~4.8mm (P95)
Why this matters
Measurable rain is possible on ~2 days. Fixed-time outdoor plans are safer with a backup option and flexible timing.
Cloud Minor
Mostly cloudy days Measures: Mostly cloudy days (cloud cover >=80%). Observed about 5% of days (1.5 days/month) in September. Historical risk signal only, not a day-by-day forecast.
Likely frequency
1.5 days / month
- Share of days
- ~5% of days
- Upper edge
- Up to ~96% (P95)
Why this matters
Mostly cloudy skies are possible on ~2 days. Fixed-time outdoor plans are safer with a backup option and flexible timing.
Rain Minor
Rainy hours Measures: Rain-hours signal (>=3h rain). Observed about 3% of days (1.0 days/month) in September. Historical risk signal only, not a day-by-day forecast.
Likely frequency
1.0 days / month
- Share of days
- ~3% of days
- Upper edge
- Up to ~11h (P95)
Why this matters
Several rainy hours are possible on ~1 days. Outdoor plans can become unreliable, so keep an indoor backup and flexibility around start times.
Wind Minor
Breezy days Measures: Breezy days (mean wind >=25 km/h). Observed about 1% of days (0.4 days/month) in September. Historical risk signal only, not a day-by-day forecast.
Likely frequency
0.4 days / month
- Share of days
- ~1% of days
- Upper edge
- Up to ~31km/h (P95)
Why this matters
Breezy conditions are possible on ~0 days. Exposed activities and transport links are more likely to be disrupted, so keep sheltered alternatives ready.
Rain Minor
Wet most of day Measures: Wet-most-of-day signal (>=6h rain). Observed about 1% of days (0.3 days/month) in September. Historical risk signal only, not a day-by-day forecast.
Likely frequency
0.3 days / month
- Share of days
- ~1% of days
- Upper edge
- Up to ~13h (P95)
Why this matters
Wet-most-of-day conditions are possible on ~0 days. Outdoor plans can become unreliable, so keep an indoor backup and flexibility around start times.
Cloud Minor
Overcast days Measures: Overcast days (cloud cover >=95%). Observed about 1% of days (0.2 days/month) in September. Historical risk signal only, not a day-by-day forecast.
Likely frequency
0.2 days / month
- Share of days
- ~1% of days
- Upper edge
- Up to ~99% (P95)
Why this matters
Overcast skies are possible on ~0 days. Fixed-time outdoor plans are safer with a backup option and flexible timing.
Heat Minor
Heatwave run Measures: Heatwave runs (>=3 hot days). Observed about 0.1 days/month in September. Historical risk signal only, not a day-by-day forecast.
Likely frequency
0.1 days / month
- Share of days
- —
- Upper edge
- Up to ~31°C (P95)
Why this matters
Heatwave runs are possible on ~0 days. Midday activity often needs adjustment around shade, hydration, and indoor fallback options.
Travel planning FAQ
Frequently asked questions
Quick answers to the weather questions you ask the most.
Is September a good time to visit San Francisco?
Typical September days in San Francisco reach highs of 22°C (72°F) with nights around 13°C (55°F). It usually feels warm by day and cool after dark. It is one of the drier months, which suits outdoor exploring and sightseeing.
What are temperatures like in September?
Daytime temperatures in September typically peak near 22°C (72°F), while nights drop to around 13°C (55°F). Expect warm afternoons and cool evenings.
How much does it rain in September?
Rainfall in September averages 3 mm (0.12 in) across roughly 1 days. Overall it is a mostly dry time of year, so showers are usually brief rather than all-day downpours.
How many hours of daylight are there in September?
You can expect about 12 hours of daylight in September. Sunrise is typically around 05:51 and sunset near 18:16. Daylight is fairly typical, with enough time for sightseeing.
How strong is the sun in September?
UV levels are often high (around 7). Regular sunscreen and a hat are recommended.
Is it windy in September?
In September, average wind speeds are around 13 km/h (8 mph), with gusts on the windiest days reaching about 51 km/h (32 mph). On the ground, it is it can feel quite windy at times, particularly when weather systems move through.