Best Month to Visit South San Francisco, California
September is the best month to visit South San Francisco. It is the warmest month of the year here, with average highs of 76°F, just 0.1 inches of rain over about two days, and wind eased to 11 mph from its early-summer peak. October is the runner-up: highs of 73°F, four rainy days, and a calmer 9 mph.
The rest of the year trades one nuisance for another. From April through July the sun is out 10 to 10.5 hours a day and rain dwindles from 1.6 inches in April to none in July, but that is also when ocean wind funnels through town at 13 to 14 mph. November through February is the calm stretch, with wind at 7 to 8 mph, and also the wet one: 8 to 12 rainy days a month and as little as 5 hours of sun a day in December.
Our picks
- Warmest and most settled weather: September. Highs of 76°F, 0.1 inches of rain on two days, and wind down to 11 mph as the fog season ends.
- Second choice with calmer air: October. Still 73°F by day with four rainy days, and wind falling to 9 mph, though nights turn cold late in the month.
- Long sunny days before summer fog: May. 10.5 hours of sun a day, highs of 69°F and half an inch of rain, with a windproof layer needed against 14 mph breezes.
At a glance
| Option | Average High (°F) | Average Low (°F) | Rainfall (in) | Rainy Days | Sunshine (hrs/day) | Wind (mph) | Season |
|---|---|---|---|---|---|---|---|
| 58source | 44source | 3.9source | 12source | 6source | 7source | Wintersource | |
| 61source | 46source | 3.7source | 11source | 7.5source | 8source | Wintersource | |
| 64source | 47source | 2.6source | 11source | 8.5source | 10source | Springsource | |
| 66source | 49source | 1.6source | 7source | 10.5source | 13source | Springsource | |
| 69source | 52source | 0.5source | 5source | 10.5source | 14source | Springsource | |
| 72source | 54source | 0.1source | 2source | 10.5source | 14source | Summersource | |
| 73source | 55source | 0source | 1source | 10source | 13source | Summersource | |
| 74source | 56source | 0source | 2source | 9.5source | 12source | Summersource | |
| 76source | 56source | 0.1source | 2source | 9source | 11source | Autumnsource | |
| 73source | 53source | 0.8source | 4source | 8source | 9source | Autumnsource | |
| 65source | 48source | 2source | 8source | 6source | 7source | Autumnsource | |
| 58source | 44source | 4.1source | 11source | 5source | 7source | Wintersource |
Why late summer beats midsummer in South San Francisco
The temperature column climbs all the way to September instead of peaking in July. July averages 73°F, August 74°F, September 76°F. Through midsummer the ocean wind keeps daytime highs down and mornings are often grey until the fog clears in the afternoon. By August and September fog stops being a daily event, and the wind has already dropped from 14 mph in June to 12 and then 11.
The whole year spans only about 18 degrees of average high, from 58°F in December and January to 76°F in September. Evenings are cool in every month; even August's average low is 56°F.
Spring and early summer: sun with a stiff breeze
On temperature and sunshine alone, April through June look like the best of it. Sunshine reaches 10.5 hours a day in all three, rain falls to 1.6 inches in April, 0.5 in May and 0.1 in June, and highs rise from 66°F to 72°F. The wind column is the counterweight: 13 mph in April and 14 in May and June, the windiest months on the calendar.
This is the city's particular quirk: it sits in a gap that funnels ocean air, and its microclimate is dominated by Pacific wind. For Sign Hill, San Bruno Mountain or the Bay Trail in May or June, the jacket that counts is one that blocks wind.
Rainy days or rainfall: reading the wet months
The two rain columns tell different stories. January, February and March each have 11 or 12 rainy days, yet March's total is 2.6 inches against February's 3.7, so March's showers are lighter. December is the wettest by volume at 4.1 inches and the darkest at 5 hours of sun a day, with the year's earliest sunset, before 5 PM, in its first week.
The upside of winter is stillness. December and January average 7 mph of wind, half of June's, and highs stay in the upper 50s. November is the gentlest of the wet months, at 65°F with 8 rainy days, though the clocks have gone back and afternoons end early.
The options in detail
January
The wettest and darkest stretch of the year in South City: rain falls on about twelve days and the sun is out roughly six hours a day, the least of any month alongside December. Highs still reach the upper 50s, so nothing here is closed by weather, but a walk up Sign Hill or along the Bay Trail is a grey, damp proposition more often than not. The compensation is wind. January is one of the calmest months in a city whose climate is otherwise dominated by ocean wind.
February
Almost a repeat of January on rain, with eleven wet days, but noticeably brighter: sunshine climbs by about an hour and a half a day and highs edge past 60. It is still the tail of the wet season, so this is a month to pack for showers rather than plan around them. The upside is that the spring wind has not arrived yet, so the afternoons you do get are usable ones.
March
The pivot month. Rain days stay high at eleven, but the totals drop by a third from February and the days lengthen fast. Wind starts to build as the ocean breeze that defines this stretch of the Peninsula strengthens through spring. A good choice if your plans are mostly indoors with outdoor options, a poor one if you need a settled forecast.
April
Rain thins out quickly in April, to roughly seven wet days and under two inches, and sunshine jumps to about ten and a half hours a day. This is where the calendar turns genuinely pleasant for Sign Hill, San Bruno Mountain and the Bay Trail. The catch is wind: April is where the afternoon sea breeze gets serious, and it stays that way into July.
May
One of the best balanced months here. Rain is nearly finished at about five days and half an inch, sunshine is at its yearly peak, and highs sit near 70 without the summer fog pattern being fully established. It is windy though, near the top of the year for it, so the layer to bring is one that blocks wind rather than one that just keeps you warm.
June
Summer starts, and in South San Francisco that means cool rather than hot. Rain essentially stops, but the marine layer arrives: mornings are frequently foggy and afternoons clear, and June is the windiest month of the year in a city whose microclimate is dominated by Pacific wind. The hills to the west shield the eastern side of town from some of the fog that sits over neighboring areas, so Oyster Point and the Bay Trail often clear earlier than the coast does. Longest days of the year, with sunset after 8:30 PM in late June.
July
The driest month on the calendar: rain is effectively zero and sunshine peaks. It is not the warmest, though, because the ocean wind running through this part of the Peninsula keeps daytime temperatures down even at midsummer. Expect grey mornings that clear by afternoon and a stiff breeze most days. If the trip is an airport, a conference and dinner on Grand Avenue, July is easy. If it is sunbathing, it is not.
August
Nearly identical to July on rain and wind but a degree or two warmer, and the clearest skies of the year across the bay. Evenings cool off fast, which is the standing lesson of a visit here: the jacket you did not think you would need. Together with September this is the part of the year when fog stops being a daily event.
September
The warmest month of the year here and, for most visitors, the best one. Highs peak in the mid 70s, rain is still essentially absent, the wind has dropped back from its summer maximum and the fog season is ending. Bay water is at its warmest too, which on this coast still means about 58 degrees. If you only get one week in South City, this is the week to take.
October
Warm days hold into October, rain is still light at about four wet days, and the wind has fallen back toward its winter calm. Nights turn cold late in the month, so evenings need a real jacket rather than a sweater. It is the last reliably dry month before the rains return, which makes it the natural second choice after September.
November
The wet season returns: rain days double from October and sunshine drops back to about six hours a day. Highs still reach the mid 60s, so it reads as mild rather than cold, and the wind is back at its yearly low. The clocks have gone back by now, so afternoons end early and outdoor plans are better made before mid-afternoon.
December
The coldest and wettest month, with rain on about eleven days and barely five hours of sun a day. The shortest day runs a little over nine and a half hours, and the earliest sunset of the year in the Bay Area falls in the first week of December, before 5 PM. Highs stay in the upper 50s, so a walk is always possible, there is just the least daylight of the year in which to take it.
How we researched this
South San Francisco has no long-record weather station of its own, so every temperature, rain, sunshine and wind figure is the 1991-2020 normal for the San Francisco airport area, about two miles away, the same set the city's own Wikipedia climate section prints. We checked that climate source against NOAA's airport normal for annual rain (19.3 inches against 19.64) and against Wikipedia's separate wind table for the city. The Season column uses Weather Atlas's month-by-month wording.
We set aside Weather Atlas's rainfall figures, which add up to about 4 inches a year against the real 19, and its temperatures, which run 2 to 5 degrees cooler than the airport normals. All 84 cells are filled. We looked for hotel rates by month as well and found no source that stated them for the city, so the table sticks to weather. These are 30-year averages rather than a forecast, so check the outlook in the days before you travel.