5-day weather forecast San Francisco Sep 18, 2026

18°15° · Sunny

Weather forecast San Francisco Friday Sep 18, 2026: sunny, temperature from 15 °C to 18 °C.

Precipitation probability 15%. Wind up to 7 m/s (gusts 8.81 m/s). Air humidity 74–90%, atmospheric pressure 763–764 mm Hg, UV index up to 6.7.

Weather Alerts

MinorSep 15, 08:42 PM — Sep 16, 04:45 AMTranslate with Google

Small Craft Advisory issued September 15 at 8:42PM PDT until September 16 at 9:00PM PDT by NWS San Francisco CA

Small Craft Advisory

* WHAT...West winds 10 to 15 kt with gusts up to 25 kt and choppy waters expected. * WHERE...San Francisco Bay South of the Bay Bridge. * WHEN...From 9 AM to 9 PM PDT Wednesday. * IMPACTS...Conditions will be hazardous to small craft.

Inexperienced mariners, especially those operating smaller vessels, should avoid navigating in hazardous conditions.

MinorSep 15, 02:17 PM — Sep 15, 10:30 PMTranslate with Google

Small Craft Advisory issued September 15 at 2:17PM PDT until September 16 at 9:00PM PDT by NWS San Francisco CA

Small Craft Advisory

* WHAT...West winds 10 to 15 kt with gusts to 25 kt and choppy waters expected. * WHERE...San Francisco Bay South of the Bay Bridge. * WHEN...From 9 AM to 9 PM PDT Wednesday. * IMPACTS...Conditions will be hazardous to small craft.

Inexperienced mariners, especially those operating smaller vessels, should avoid navigating in hazardous conditions.

5 days at a glance — tap a day to open it

Sunrise 06:54
Sunset 19:13

First Quarter53% illuminated
Moonrise 15:01 · Moonset does not set today

Chart

Table

← Thu, Sep 17

Fri, Sep 18, 2026

Sat, Sep 19 →

Forecast from 15 °C to 18 °C and precipitation

Temperature & Precipitation
Time	00:00	01:00	02:00	03:00	04:00	05:00	06:00	07:00	08:00	09:00	10:00	11:00	12:00	13:00	14:00	15:00	16:00	17:00	18:00	19:00	20:00	21:00	22:00	23:00
Temperature (°C)	16	16	15	15	15	15	15	15	15	16	17	17	18	18	17	17	17	17	16	16	15	15	15	15
Precipitation (mm/hr)	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0

Cloud cover and precipitation probability

Cloud cover & Rain chance
Time	00:00	01:00	02:00	03:00	04:00	05:00	06:00	07:00	08:00	09:00	10:00	11:00	12:00	13:00	14:00	15:00	16:00	17:00	18:00	19:00	20:00	21:00	22:00	23:00
Cloud cover (%)	0	0	1	5	4	2	2	1	0	0	0	0	3	12	19	29	16	14	14	15	24	21	22	21
Rain chance (%)	12	12	12	13	13	13	13	13	12	10	9	8	7	8	9	11	10	10	11	12	14	14	15	14

Wind speed and direction

Wind & Wind gust
Time	00:00	01:00	02:00	03:00	04:00	05:00	06:00	07:00	08:00	09:00	10:00	11:00	12:00	13:00	14:00	15:00	16:00	17:00	18:00	19:00	20:00	21:00	22:00	23:00
Wind (m/s)	2.69	2.39	2.31	1.81	1.5	1.61	1.19	1	1.31	1.31	1.39	1.81	2.69	3.81	4.39	5	6.31	7	6.19	5.11	4.69	4.5	5.11	4.81
Wind gust (m/s)	4	3.22	3.03	2.31	1.92	1.81	1.33	1	1.39	5.31	5.39	5.81	5.69	8.81	4.5	6.31	7.81	8.61	8.42	7.14	6.5	6.61	7	6.69
Wind direction (°)	W 279°	W 271°	W 271°	WSW 253°	WSW 247°	SW 216°	WSW 238°	SSW 205°	SSW 195°	SW 234°	WSW 244°	WSW 252°	WSW 255°	WSW 257°	W 259°	W 262°	W 268°	W 272°	W 276°	W 276°	W 272°	W 263°	W 264°	W 266°

Air humidity

Humidity
Time	00:00	01:00	02:00	03:00	04:00	05:00	06:00	07:00	08:00	09:00	10:00	11:00	12:00	13:00	14:00	15:00	16:00	17:00	18:00	19:00	20:00	21:00	22:00	23:00
Humidity (%)	86	87	88	89	90	90	90	90	87	82	79	76	74	75	76	78	78	79	82	85	88	88	88	89

Atmospheric pressure

Pressure
Time	00:00	01:00	02:00	03:00	04:00	05:00	06:00	07:00	08:00	09:00	10:00	11:00	12:00	13:00	14:00	15:00	16:00	17:00	18:00	19:00	20:00	21:00	22:00	23:00
Pressure (mm Hg)	764	764	764	764	764	764	764	764	764	764	764	764	764	764	764	764	763	763	763	763	763	763	763	763

Ultraviolet index

UV Index
Time	00:00	01:00	02:00	03:00	04:00	05:00	06:00	07:00	08:00	09:00	10:00	11:00	12:00	13:00	14:00	15:00	16:00	17:00	18:00	19:00	20:00	21:00	22:00	23:00
UV Index	0	0	0	0	0	0	0	0	0.3	1.1	2.5	4.3	5.9	6.7	6.3	5	3.2	1.4	0.4	0	0	0	0	0

Air quality & pollen

Air quality
Time	00:00	01:00	02:00	03:00	04:00	05:00	06:00	07:00	08:00	09:00	10:00	11:00	12:00	13:00	14:00	15:00	16:00	17:00	18:00	19:00	20:00	21:00	22:00	23:00
PM2.5 (µg/m³)	14.8	15.3	15.4	15.6	15.4	15.3	14.6	14.1	13.5	12.4	12.3	12.3	12.4	12.5	12.2	11.6	11.2	11.1	11	10.9	10.8	11.1	11.2	11.3
PM10 (µg/m³)	19.7	19.9	20.4	20.7	20.5	20.4	19.6	18.7	18.2	16.8	16.5	16.5	16.6	16.8	16.5	15.8	15.3	15.3	15.5	15.6	15.7	16.3	16.6	16.8
Ozone (O₃) (µg/m³)	60	60	61	62	65	67	70	73	76	79	83	86	90	94	96	95	92	89	87	85	83	81	79	77
NO₂ (µg/m³)	19.3	19.1	18.4	16.9	14.8	12.8	11.2	9.8	8.5	7.5	6.6	5.8	5	4.3	3.8	3.7	3.8	4	4.2	4.5	4.7	4.7	4.6	4.5
SO₂ (µg/m³)	1.5	1.4	1.4	1.4	1.4	1.4	1.4	1.4	1.4	1.4	1.4	1.4	1.4	1.3	1.2	1.1	1	0.9	0.8	0.7	0.7	0.7	0.8	0.9
CO (µg/m³)	144	136	130	127	127	128	131	136	139	140	139	139	139	138	138	138	137	137	137	138	138	137	135	133

← Thu, Sep 17

Fri, Sep 18, 2026

Sat, Sep 19 →

San Francisco on the map

Data Sources & Methodology

Our weather forecasts are powered by a professional weather data provider that aggregates data from national weather services, satellite observations, radar networks, and over 80,000 weather stations worldwide. Forecast data is updated multiple times daily. We convert raw data into clear summaries — wind speed in m/s, pressure in mmHg — so you can plan your day with confidence.

Learn more about our methodology →