Fullerton, United States experiences average highs of 25°C (77°F) and lows of 13°C (55°F) throughout the year. The climate is relatively dry, with only 3 rainy days per month on average. Sunshine is abundant, averaging about 11 hours per day. Average highs have cooled by 0.8°C (1.4°F) across the available records.
Fullerton, United States Weather & Climate 2026
Monthly climate averages for Fullerton, United States. Based on 10-year ERA5 reanalysis data.
Climate Overview
Drier season: Apr–Oct 
Wetter season: Jan–Dec At-a-Glance Climate Summary
Live Weather & Air Quality
Key figures
Climate Score
8.6/10
Best: April, May, June, September, October
UV Index
6
High
Temperature 25°C / 13°C
Feels Like 25°C / 13°C
Rainy Days 3
Rainfall 27 mm
Sunshine 11 h
Humidity 66%
Wind Speed 16 km/h
Dew Point 13°C
Hottest Month
32°C
August
Avg Low19°C
Rain0days
Coldest Month
7°C
January
Avg High19°C
Rain6days
Driest Month
0days
July
Avg High31°C
Avg Low19°C
Windiest Month
18 km/h
April (Gusts 36)
Sea Temperature
15°C – 22°C
Warmest water: August (
22.3°C
)
Worst Time to Visit
Consider avoiding January, February, March, December due to less favorable weather conditions.
Sun Position
Sunrise 05:42
Daylight 14.4h
Sunset 20:05
Live conditions—
Fullerton on the map · live conditions
Fullerton, United States
- Continent
- Americas
- Country
- United States
- City
- Fullerton
- Population
- 140.8K
- Elevation
- 50 m
- Coordinates
- 33.87°, -117.93°
Seasonal Breakdown
Spring
Mar–May
Avg High 23°C
Avg Low 12°C
Rain 4 days/mo
2/3 best months
Summer
Jun–Aug
Avg High 31°C
Avg Low 18°C
Rain 0 days/mo
1/3 best months
Autumn
Sep–Nov
Avg High 28°C
Avg Low 15°C
Rain 2 days/mo
2/3 best months
Winter
Dec–Feb
Avg High 20°C
Avg Low 8°C
Rain 5 days/mo
Climate Charts
Based on historical averages (2016–2025)
Monthly Temperatures
HighLowShaded bands show the typical range across the available yearly records.
Line chart showing monthly temperatures. Jan: 19°C / 7°C . Feb: 20°C / 8°C . Mar: 20°C / 9°C . Apr: 24°C / 12°C . May: 24°C / 14°C . Jun: 28°C / 16°C . Jul: 31°C / 19°C . Aug: 32°C / 19°C . Sep: 31°C / 19°C . Oct: 28°C / 15°C . Nov: 24°C / 11°C . Dec: 20°C / 8°C .
Monthly Rainfall
Rainfall
Bar chart showing monthly rainfall. Jan: 73 mm. Feb: 61 mm. Mar: 59 mm. Apr: 16 mm. May: 7 mm. Jun: 2 mm. Jul: 1 mm. Aug: 6 mm. Sep: 5 mm. Oct: 9 mm. Nov: 27 mm. Dec: 57 mm.
Monthly Humidity
Humidity
Line chart showing monthly humidity. Jan: 72%. Feb: 68%. Mar: 72%. Apr: 66%. May: 68%. Jun: 65%. Jul: 63%. Aug: 64%. Sep: 65%. Oct: 62%. Nov: 61%. Dec: 68%.
Monthly Wind Speed
Wind SpeedGusts
Bar chart showing monthly wind speed. Jan: 13 km/h . Feb: 16 km/h . Mar: 18 km/h . Apr: 18 km/h . May: 17 km/h . Jun: 16 km/h . Jul: 16 km/h . Aug: 16 km/h . Sep: 16 km/h . Oct: 15 km/h . Nov: 14 km/h . Dec: 13 km/h .
Sunshine
Sunshine
Sunshine: Jan: 8h. Feb: 9h. Mar: 10h. Apr: 11h. May: 12h. Jun: 13h. Jul: 13h. Aug: 12h. Sep: 11h. Oct: 10h. Nov: 9h. Dec: 8h.
Sea Temperature
Sea Temperatureswim
Line chart showing monthly sea temperature. Jan: 15°C . Feb: 15°C . Mar: 15°C . Apr: 16°C . May: 18°C . Jun: 20°C . Jul: 21°C . Aug: 22°C . Sep: 22°C . Oct: 20°C . Nov: 18°C . Dec: 16°C .
UV Index
UV Index
Bar chart showing monthly UV index. Jan: UV 4. Feb: UV 4. Mar: UV 6. Apr: UV 7. May: UV 8. Jun: UV 8. Jul: UV 9. Aug: UV 8. Sep: UV 7. Oct: UV 6. Nov: UV 4. Dec: UV 3.
Monthly Daylight Hours
Daylight12h reference
Monthly Dew Point & Comfort
Dew Point Dry Comfortable Humid Muggy Oppressive
Climate Trends
Average highs have cooled by 0.8°C (1.4°F) across the available records. Average rainfall is trending wetter by about 11 mm.
2016 to 2025
Avg high Avg rainfall
Climate summary
| Last 12 months | All years | |
|---|---|---|
| Hottest month | Aug 2025 · 32°C | Aug · 32°C |
| Coldest month | Jan 2025 · 6°C | Jan · 7°C |
| Wettest month | Nov 2025 · 116 mm | Jan · 73 mm |
| Windiest month | Mar 2025 · 19 km/h | Apr · 18 km/h |
Month-by-Month Weather Table
January
Good 
February
Good March
Good April best
Excellent May best
Excellent June best
Excellent July
Good August
Excellent September best
Excellent October best
Excellent November
Excellent December
Good | Month | Temp | Feels Like | Rain | Sun | Humidity | UV | Status | Details |
|---|---|---|---|---|---|---|---|---|
| January | 19°C / 7°C | 17°C / 5°C | 6days (73 mm) Good | 8.2h Good | 72% Muggy | 3.7 Moderate | Good | View Details |
| February | 20°C / 8°C | 18°C / 5°C | 5days (61 mm) Good | 9h Good | 68% Muggy | 4.4 Moderate | Good | View Details |
| March | 20°C / 9°C | 19°C / 8°C | 8days (59 mm) Wet | 10.1h Excellent | 72% Muggy | 6.1 High | Good | View Details |
| April best | 24°C / 12°C | 23°C / 11°C | 2days (16 mm) Excellent | 11.4h Excellent | 66% Muggy | 7.2 Very High | Excellent | View Details |
| May best | 24°C / 14°C | 24°C / 13°C | 2days (7 mm) Excellent | 12h Excellent | 68% Muggy | 7.8 Very High | Excellent | View Details |
| June best | 28°C / 16°C | 29°C / 17°C | 1days (2 mm) Excellent | 13h Excellent | 65% Muggy | 8.3 Very High | Excellent | View Details |
| July | 31°C / 19°C | 33°C / 20°C | 0days (1 mm) Excellent | 13.2h Excellent | 63% Muggy | 8.5 Very High | Good | View Details |
| August | 32°C / 19°C | 34°C / 21°C | 0days (6 mm) Excellent | 12.1h Excellent | 64% Muggy | 7.9 Very High | Excellent | View Details |
| September best | 31°C / 19°C | 32°C / 20°C | 1days (5 mm) Excellent | 11.2h Excellent | 65% Muggy | 7 High | Excellent | View Details |
| October best | 28°C / 15°C | 27°C / 15°C | 2days (9 mm) Excellent | 10.1h Excellent | 62% Muggy | 5.6 High | Excellent | View Details |
| November | 24°C / 11°C | 22°C / 9°C | 3days (27 mm) Excellent | 9h Good | 61% Muggy | 4.2 Moderate | Excellent | View Details |
| December | 20°C / 8°C | 18°C / 6°C | 5days (57 mm) Good | 7.9h Good | 68% Muggy | 3.4 Moderate | Good | View Details |
Compare Nearby City Climates
Frequently Asked Questions
The best months to visit Fullerton are April, May, June, September, October, when temperatures are comfortable and rainfall is at its lowest. This is based on 10-year climate averages for Fullerton, scoring temperature, rainfall, humidity, and sunshine hours.
The hottest month in Fullerton is August, with average daytime highs of 32°C (90°F). Plan outdoor activities for early morning or late afternoon if visiting during this period.
The coldest month in Fullerton is January, with average overnight lows of 7°C (45°F). Pack warm layers and expect shorter daylight hours during this period.
The wettest month in Fullerton is January, averaging 73mm of precipitation across 6 rainy days. An umbrella or waterproof jacket is essential.
Fullerton receives approximately 127 sunshine hours per year. The sunniest month is July with around 13 hours. Based on climate data for Fullerton.
The least favorable months to visit Fullerton are January, February, March, December, primarily due to less favorable weather conditions. For the best conditions, consider April, May, June, September, October instead.
The annual average UV index in Fullerton is 6, classified as high. Standard sun protection (sunscreen, hat) is recommended during prolonged outdoor exposure.
Average humidity in Fullerton is 66%, classified as moderate. Humidity levels are generally comfortable and should not affect outdoor activities for most people.
Yes — sea temperatures in August average 22°C (72°F), which is warm and comfortable for swimming and water activities.
Average wind speeds in Fullerton are 16 km/h (10 mph). The windiest month is April with peak winds reaching 18 km/h (11 mph) (gusts up to 36 km/h / 22 mph).
Fullerton averages 7 clear-sky days per month with overall cloud cover around 42%. The clearest skies occur in October.
The annual average dew point in Fullerton is 13°C (55°F), which feels pleasant with low humidity. Outdoor activities are comfortable year-round from a humidity standpoint.
Fullerton has a Hot Semi-Arid climate, classified as BSh under the Köppen system. Arid climates have very low rainfall relative to temperature, with large swings between daytime heat and cool nights.
The 'feels like' temperature in Fullerton ranges from 13°C (55°F) to 25°C (77°F) on average. The 'feels like' temperature closely matches the actual temperature throughout most of the year.
Yes, June is a great time to visit Fullerton. It earns a climate score of 9.3/10 with Excellent.
For June in Fullerton, pack Breathable clothing, Sunscreen (SPF 30+), Sun hat, Sunglasses, Sandals. With average highs of 28°C (83°F) and 1 rainy days, these essentials will keep you comfortable.
Data Source
Climate data derived from ERA5 reanalysis (ECMWF), averaged over 2016–2025. Sea surface temperature from marine reanalysis data. Climate scores and seasonal estimates are computed by WorldStats.
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