San Francisco is a unique city where it’s surrounded by sea on three of its side. Its climate is very unique, where you always have around the same temperature, 1-10°-16°C (50°-70°F). The sun is warm when it shines, but the wind is forever cold. The wind is cold because of it’s coming from the sea where ocean currents come from the Caribbean and tropical Atlantic. The Pacific Ocean current moves southward along the western coast of North America, beginning off southern British Columbia (west of Canada) and ending off southern Baja California Peninsula (west of Mexico).
Coming from a tropical country gave me the perception that beach is warm or hot. I suggest you dress in layers when you visit San Francisco. Even in summer.
This is a picture of my wife that I took with my phone enjoying the rare sunshine in Union Square, the center of the city.