Weather in Costa Mesa, California
Fog and sun in daily rhythm. Day 59 of spring. Read this microseason across nine climate regions →
- TodayMay 16Overcast—71°60°
- SundayMay 17Overcast—69°57°
- MondayMay 18Overcast—71°54°
- TuesdayMay 19Overcast—76°62°
- WednesdayMay 20Overcast—76°63°
- ThursdayMay 21Overcast—74°63°
- FridayMay 22Clear—76°63°
- PM 2.5
- 10.8 μg/m³
- PM 10
- 17.3 μg/m³
- NO₂
- 2.7 μg/m³
- Ozone
- 95.0 μg/m³
- UV Index
- 0.1 Low
When the dew is on the grass, rain will never come to pass.
- Moonrise
- 1:06 PM
- Moonset
- 3:15 AM
- In sign
- ♉︎ Taurus
Fog and sun in daily rhythm
Costa Mesa at a glance
- Today vs. normal: 14°F below the seasonal normal for this latitude
- Last frost: March 9 (climatological average for this latitude)
- Microseason: 28 of 72, May 16–20
- Planting window: Direct sow okra, melons, and southern peas. Thin carrot rows.
Right now in the garden
Peak growing season
As of May 17, 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.