Today | Weather | Tuesday, July 21, 2026

Active Weather Warnings

High Surf Advisory

Weather in Costa Mesa, California

03:12 AM

Now

70° F

Feels Like 70°

Precipitation 0 %

Wind 5 mph

Humidity 88 %

Today

Day 82°

Night 72°

Precipitation 0 %

Wind 8 mph

UV Index (0 - 11+) 11

Warning: Extreme UV Index Today: 11

Overexposure to the sun's harmful UV rays can cause sunburn and increase the risk of developing skin cancer, including melanoma. Protect yourself by wearing clothing that covers your skin, sunglasses, and a hat. Apply a broad-spectrum sunscreen with an SPF of 30 or higher every two hours, even on cloudy days. Minimize direct sun exposure during peak hours (10 AM to 4 PM) to reduce the risk.

Costa Mesa Weather Forecast Updated

34 minutes ago

Last updated on July 21, 2026 at 2:38 AM

Weather Forecast History

Last Year's Weather on This Day (July 21, 2025)

Day

75°

Night

66°

Wind

6 mph

Precipitation

25 %

Air Quality in Costa Mesa

NOW

33 AQI

Good air quality Dominant pollutant: O₃

Pollutant Concentrations:

PM_2.5 5.9 µg/m³

PM₁₀ 14.7 µg/m³

O₃ 0.036 ppm

NO₂ 0.3 ppb

SO₂ 0.2 ppb

CO 0.07 ppm

NH₃ 0 µg/m³

NO 0 µg/m³

PM_2.5 – Fine particles <2.5μm

PM₁₀ – Inhalable particles <10μm

O₃ – Ozone

NO₂ – Nitrogen dioxide

SO₂ – Sulfur dioxide

CO – Carbon monoxide

NH₃ – Ammonia

NO – Nitric oxide

Health Recommendations:

Air quality is considered satisfactory, and air pollution poses little or no risk.

Show raw pollutant concentrations (µg/m³)

PM_2.5 – 5.9 µg/m³

PM₁₀ – 14.7 µg/m³

O₃ – 70.18 µg/m³

NO₂ – 0.65 µg/m³

SO₂ – 0.63 µg/m³

CO – 83.05 µg/m³

NH₃ – 0 µg/m³

NO – 0 µg/m³

View Hourly Air Quality Forecast

Weather Alerts and Warnings for Costa Mesa

Minor Expected Likely

High Surf Advisory

High Surf Advisory issued July 20 at 2:06PM PDT until July 21 at 11:00PM PDT by NWS San Diego CA

Jul 20, 2:06 PM → Jul 21, 11:00 PM

WHAT: Large breaking waves of 4 to 7 feet with sets up to 8
feet at south or southwest facing beaches.

WHERE: San Diego County Coastal Areas and Orange County
Coastal Areas.

WHEN: Until 11 PM PDT Tuesday.

IMPACTS: Dangerous swimming and surfing conditions and
localized beach erosion.

ADDITIONAL DETAILS: South swell of 4 to 5 feet with a period
of 11-13 seconds generating high surf, primarily for south-
facing beaches. High risk of rip currents exists with high
surf and strong longshore currents are expected on west-facing
beaches. High tides will generally be at or below 5.5 feet,
but localized areas of beach erosion and minor tidal overflow
may occur with the high surf during high tides. Swell and surf
will decrease late Tuesday into Wednesday.

+ Read More

Inexperienced swimmers should remain out of the water due to dangerous surf conditions.

Updated: Jul 21, 2:38 AM Source: NWS Alert