San Francisco Weather in September
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North America › 🇺🇸 United States › San Francisco
Updated: March 2026
Is September a Good Time to Visit San Francisco?
September is a excellent time to visit San Francisco (8/10). With 12 daily sunshine hours and only 0 rain days, this month delivers genuinely reliable outdoor conditions, ranking it 5th sunniest of the year in San Francisco. Beach and outdoor-focused visitors will find September ideal, though hotel prices reflect demand and popular sites get crowded by mid-morning. October offers a similar profile at lower hotel rates if dates are flexible. The main practical note: San Francisco's popular sites are busiest between 10am and 3pm regardless of season. Arriving at opening time or after 4pm makes a significant difference to the experience. Planning tips: book accommodation at least 6-8 weeks ahead, as popular hotels fill quickly during September. Purchasing skip-the-line tickets for major attractions in advance saves meaningful time. If you have flexibility, arriving a few days before or after peak weekends reduces both crowds and prices noticeably.
The single most important thing to know about visiting San Francisco in September: conditions are genuinely cooperative, with 23°C highs and only 0 wet days making this one of the more straightforward months to plan around. Precipitation totals 2mm for the month, spread across roughly 0 days, and 12 sunshine hours per day give you a reliable window for outdoor plans.
23°C
Avg High
13°C
Avg Low
0 days
Rain Days
12h
Sunshine
65%
Humidity
Temperature in San Francisco in September
The 10°C day-night temperature range is typical for continental climates: a light jacket in the morning that you shed by midday and need again after sunset. Humidity averages 65%, which is comfortable for most visitors. On warmer days, lighter fabrics help with the mild stickiness in the afternoon. UV index averages 6 this month, classed as moderate. Sunscreen is a sensible precaution for extended outdoor time, particularly at midday. Wind averages 18 km/h, light enough to be refreshing on warm days but noticeable in open coastal areas or elevated viewpoints. In Fahrenheit: 73°F average high, 55°F overnight low. Data sourced from Open-Meteo ERA5 climate reanalysis (1991–2020 normals).
Temperature in September
Monthly Precipitation (mm)
What to Wear in San Francisco in September
Packing for San Francisco in September means dressing for 23°C days and 13°C evenings. A light cotton tee with a casual overshirt works well at 23°C, the overshirt doubles as a layer for air-conditioned venues. Evening temperatures settle at 13°C, a modest 10°C drop that a light cardigan or denim jacket covers. Comfortable walking trainers are the versatile choice for both outdoor sightseeing and indoor venues.
Local tip: Layers are more practical than a single heavy garment in San Francisco. The day-to-evening temperature shift rewards packing a versatile mid-layer you can add or remove as conditions change.
Events in San Francisco in September
September has no major festivals or public holidays in San Francisco, which is one of its practical advantages for independent travellers. Attractions run at lower capacity than during peak event periods, queues are shorter, and accommodation is easier to find without needing to book many months in advance. Local restaurants, markets, and transport operate at a relaxed pace, making this an ideal time for visitors who prefer a more authentic, unhurried experience of everyday city life rather than large crowds drawn in by a single major headline event.
What to Pack for San Francisco in September
Based on 23°C average highs and 0 rainy days
- Light layers for morning and evening
- Breathable T-shirts and comfortable trousers
- UV-protective sunglasses
- SPF 30+ sunscreen
- Comfortable walking shoes (a second pair lets the first air out overnight)
- Universal travel adapter
- Small day pack for city exploration
- Reusable water bottle
Best Activities in San Francisco in September
- Explore outdoor markets and street food stallsMid-morning (10am-12pm)At 23°C, the temperature is ideal for extended walking without overheating
- Guided walking tour of the historic centreMorning or late afternoonComfortable temperatures allow several hours on foot without fatigue
- Visit rooftop viewpoints and observation decksGolden hour (1 hour before sunset)Warm clear evenings provide exceptional visibility for panoramic photography
- Day trip to the surrounding countryside or coastFull day (depart by 8am)September is reliably dry enough for rural day trips without weather risk
- Afternoon in a world-class museum or galleryAfternoon (2-5pm)Pairs well with outdoor morning activities and provides a mid-day rest from sightseeing
- Coffee-house or traditional cafe culture experienceMid-morning or post-lunchA cultural ritual in this region that rewards slow appreciation regardless of weather
- Evening live music, theatre, or opera performanceEvening shows typically at 7-9pmConsistent evening temperatures make getting to and from evening venues comfortable
- Visit the main botanical garden or city park at seasonal peakYear-round; best light in morningSeptember brings distinct seasonal changes to public green spaces worth exploring
- Try the seasonal farmer's market for local produce and street foodSaturday morning markets typically 8am-1pmSeptember seasonal produce is at peak availability, offering dishes not found at other times of year
Why is San Francisco mild in September?
September brings the first meaningful shift toward cooler conditions in San Francisco, as the sun angle drops and day length shortens. Temperatures averaging 23°C by day and 13°C overnight are still comfortable by most standards, but the trend is clearly downward. At 38 degrees north latitude, autumn light has a particular quality: lower in the sky and warmer in tone, it gives the city a photogenic quality quite different from summer. Conditions remain excellent for outdoor activity, and crowds thin compared to the summer peak. Climate data: Open-Meteo ERA5 (1991–2020).
Sunshine Hours
The average number of hours per day with direct sunlight. Calculated from satellite measurements. Days with more than 7 hours of sunshine are ideal for outdoor activities. Under 3 hours means overcast conditions dominate.
UV Index
A scale from 0-11+ measuring ultraviolet radiation intensity. UV 0-2: Minimal risk. UV 3-5: Moderate -- wear sunscreen. UV 6-7: High -- hat and SPF 30+ essential. UV 8-10: Very High -- limit midday exposure. UV 11+: Extreme -- seek shade between 10am-4pm.
Rain Days
A rain day is counted when precipitation exceeds 0.1mm. This threshold captures even light drizzle. Unlike total rainfall in mm, rain days tells you how often you might need an umbrella, which is useful for planning outdoor activities.
Humidity
Relative humidity as a percentage. Below 40%: Dry -- skin and throat may feel parched. 40-60%: Comfortable -- ideal for most people. 60-80%: Sticky -- light, breathable fabrics recommended. Above 80%: Muggy -- heat feels more intense; quick-dry clothing is essential.
Frequently Asked Questions: San Francisco in September
September ranks 5th sunniest of the year in San Francisco, with an average 12 daily sunshine hours. The driest months are July, August, and September. September is the hottest month (23°C avg high); January is the coolest (14°C). From here, temperatures fall 2°C into October. Compared to last month (August: 22°C high, 0 rain days), September is warmer and equally dry. September sits in the middle of the annual sunshine ranking for San Francisco, offering a reasonable balance of good weather and manageable crowds.
Year-Round Climate
Plan Your Trip to San Francisco
Data Sources for San Francisco
Climate normals represent 30-year averages (1991-2020). Individual years may vary.