Costa Mesa, California Weather
Coastal fog thickens at dawn. Day 77 of spring. Read this microseason across nine climate regions →
Costa Mesa weather forecast — hour by hour, 7-day outlook, NOAA radar
- TodayJun 3Overcast——72°59°—
- ThursdayJun 4Foggy——72°61°0°
- FridayJun 5Overcast——71°59°-1°
- SaturdayJun 6Overcast——74°64°+3°
- SundayJun 7Mostly Clear——76°62°+2°
- MondayJun 8Clear——74°63°-2°
- TuesdayJun 9Clear——77°63°+3°
PM2.5 at 12.8 µg/m³, PM10 at 22.3 µg/m³ — typical background levels with no transport signature. AQI flat over the last 6 hours (within ±3 points).
OK No precautions needed for the general population; unusually sensitive individuals may consider limiting prolonged outdoor exertion.
What's driving it
Ozone × UV × Sky
Ozone at AQI 36 now. With UV 0.0 peaking around 1 PM under clear skies, surface ozone likely climbs to AQI 9 by mid-afternoon.
- Present
- AQI 36
- UV peak
- 0.0 at 1 PM
- Sky at peak
- clear
- Projected peak
- AQI 9
PM × Wind × Precip
PM2.5 at 12.8 µg/m³, PM10 at 22.3 µg/m³ — typical background levels with no transport signature.
- PM2.5/PM10
- 0.57
- Wind
- calm
- Recent rain
- 0h in last 6h
- Pattern
- background
Trends
Seven days of AQI and PM2.5.
Hourly air-quality data from the Copernicus Atmosphere Monitoring Service, charted across the past and next several days. Dashed lines mark the AQI breakpoints at 50 (Good → Moderate) and 100 (Moderate → Unhealthy for Sensitive Groups).
A summer fog for fair, a winter fog for rain.
- Moonrise
- 6:04 AM
- Moonset
- 4:16 PM
- In sign
- ♑︎ Capricorn
Coastal fog thickens at dawn
Costa Mesa at a glance
- Today vs. normal: 18°F below the seasonal normal for this latitude
- Last frost: March 9 (climatological average for this latitude)
- Microseason: Jun 1–5
- Planting window: Harvest spring lettuce before it bolts. Sow heat-tolerant greens.
Right now in the garden
Peak growing season
As of June 4, the growing season is at its peak — frost is months away. Continue succession-planting beans and summer squash. Start fall brassicas (broccoli, cabbage, kale) from seed indoors for transplanting in late summer.
Planting calendar
| Month | Plant | Harvest |
|---|---|---|
| January | — | — |
| February | — | — |
| March | lettuce, peas, spinach, radishes | — |
| April | lettuce, peas, spinach, radishes, tomatoes, peppers, beans, squash | — |
| May | tomatoes, peppers, beans, squash | lettuce, peas, radishes |
| June | tomatoes, peppers, beans, squash | lettuce, peas, radishes |
| July | — | tomatoes, beans, summer squash |
| August | — | tomatoes, beans, summer squash |
| September | — | tomatoes, beans, summer squash |
| October | fall brassicas, garlic (overwinter), carrots | winter squash, tomatoes (last) |
| November | fall brassicas, garlic (overwinter), carrots | — |
| December | — | — |
A year in weather
Costa Mesa's warmest month is August (~75°F mean) and its coldest is December (~58°F). Rainfall peaks in February (3.2 inches) and bottoms out in August (0.0 inches).
| Month | Mean temp | Precip | Rainy days |
|---|---|---|---|
| January | 59° | 2.9″ | 5 |
| February | 59° | 3.2″ | 5 |
| March | 62° | 1.7″ | 3 |
| April | 64° | 0.8″ | 2 |
| May | 66° | 0.3″ | 1 |
| June | 70° | 0.1″ | 0 |
| July | 74° | 0.0″ | 0 |
| August | 75° | 0.0″ | 0 |
| September | 74° | 0.1″ | 0 |
| October | 69° | 0.5″ | 1 |
| November | 63° | 0.8″ | 2 |
| December | 58° | 2.2″ | 4 |
Regional context
Costa Mesa sits within a hot-summer Mediterranean climate region — a cohort that shares similar temperature ranges, seasonal patterns, and growing conditions across nearby cities.
Similar climates: Los Angeles, CA, San Francisco, CA, San Diego, CA, Riverside, CA, Sacramento, CA.
Naturalist notes
By late May in coastal Southern California, western scrub jays are gathering nesting material and carrying it into live oaks and ornamental pines at the latitude of Costa Mesa.
Late spring sunsets near 33.7°N extend twilight past 8 PM, and Venus often sits bright and unmistakable in the western sky well before full dark arrives.
Frequently asked
- When does it freeze in Costa Mesa?
- Costa Mesa's last spring frost typically falls around mid-March, and the first fall frost arrives around mid-December.
- What is the rainy season in Costa Mesa?
- February is the wettest month with about 3.2 inches of rain on average; the city receives roughly 13 inches annually.
- What is the warmest month in Costa Mesa?
- August is typically warmest, averaging about 75°F.
- What is the coldest month in Costa Mesa?
- December is typically coldest, averaging about 58°F.
- When can I start a vegetable garden in Costa Mesa?
- Cool-season crops (peas, lettuce) can be sown around the last spring frost (mid-March); warm-season crops (tomatoes, peppers) wait until 1–2 weeks after.
- How many rainy days does Costa Mesa get?
- Costa Mesa averages about 22 rainy days per year.
- What hardiness zone is Costa Mesa?
- Costa Mesa's hardiness zone is set by its lowest average winter temperature; check the USDA's online lookup with the city ZIP for the current zone designation.
Climate
Costa Mesa, California sits in a hot-summer Mediterranean climate zone. January means hover near 59°F, while July averages 74°F — a 15°F seasonal swing.
Across the year, Costa Mesa receives about 13 inches of precipitation spread over roughly 22 rainy days.
The rhythm of the year is set by latitude (33.7°N), proximity to large water bodies, and elevation — all of which shape what grows here, when frost is likely, and what the weather story looks like day to day.