Will I be hot?
Will I be hot in San Francisco in September?
Verdict
No — No, comfortable.
Highs cap at 70°F — no heat-management gear needed.
Day vs. night
Day
70°F
Comfortable
A T-shirt and a light overshirt is enough.
Night
57°F
Cool
You'll want a warm layer after sunset — not a heavy coat.
Why
San Francisco in September averages highs of 70°F, lows of 57°F, 2 rainy days.
Temperature is comfortable across the day; pack for style and weather resistance, not heat management.