Today | Weather | Friday, October 9, 2026
Active Weather Warnings

Weather in San Mateo, California

09:44 AM
Now
Cloudy Weather
66° F
Feels Like 64°
Precipitation 0 %
Wind 5 mph
UV Index (0 - 11+) 1
Humidity 76 %
Today
Cloudy Weather
Day 73°
Night 57°
Precipitation 0 %
Wind 8 mph
UV Index (0 - 11+) 4

San Mateo Weather Forecast Updated

Last updated on
Weather Forecast History
Last Year's Weather on This Day (October 9, 2025)
Cloudy Night

Day

72°

Night

54°

Wind

6 mph

Precipitation

4 %

Air Quality in San Mateo

NOW
48 AQI
Good air quality Dominant pollutant: PM2.5

Pollutant Concentrations:

PM2.5 11.56 µg/m³
PM10 27.89 µg/m³
O3 0.042 ppm
NO2 0.6 ppb
SO2 0.4 ppb
CO 0.12 ppm
NH3 0 µg/m³
NO 0.08 µg/m³
PM2.5 – 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)
PM2.5 – 11.56 µg/m³
PM10 – 27.89 µg/m³
O3 – 82.45 µg/m³
NO2 – 1.12 µg/m³
SO2 – 1.02 µg/m³
CO – 133.04 µg/m³
NH3 – 0 µg/m³
NO – 0.08 µg/m³

Weather Alerts and Warnings for San Mateo

Minor Expected Likely

Coastal Flood Advisory

Coastal Flood Advisory issued October 8 at 9:45PM PDT until October 13 at 3:00PM PDT by NWS San Francisco CA
Oct 9, 9:00 AM → Oct 13, 3:00 PM
WHAT: Up to 1.4 ft of inundation above ground level is
possible in low-lying areas near shorelines and tidal
waterways.

WHERE: Bayshore locations along the San Francisco and
Monterey Bays.

WHEN: From 9 AM Friday to 3 PM PDT Tuesday.

IMPACTS: Flooding of lots, parks, and roads with only
isolated road closures expected. High tides will result in
flooding along coastal trails, cut off access to some low-
lying beaches and coastal areas, and bring water and waves
farther up the beach than typical.

ADDITIONAL DETAILS: At the San Francisco tidal gauge, high tide
is expected to be 1.2 ft above normal (7.1 ft MLLW) at 11:22 AM
Friday 10/9, 1.4 ft above normal (7.3 ft MLLW) at 11:50 AM
Saturday 10/10, 1.3 ft above normal (7.2 ft MLLW) at 12:18 PM
Sunday 10/11, 1.2 ft above normal (7.1 ft MLLW) at 12:46 PM
Monday 10/12, and 1.1 ft above normal (7.0 ft MLLW) at 1:14 PM
Tuesday 10/13. These predictions include up to 1.2 ft of surge
that will enhance the astronomical tide and flooding threat.
High tide varies up to 90 minutes earlier or later along the
Pacific Coast and through the San Francisco Bay, respectively.
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If travel is required, allow extra time as some roads may be closed. Do not drive around barricades or through water of unknown depth. Take the necessary actions to protect flood-prone property.
Updated: Oct 9, 8:40 AM Source: NWS Alert