A pleasant Saturday on land comes with a more serious warning on the water: the National Weather Service has a Small Craft Advisory in effect on San Francisco Bay until 9 p.m. Saturday.
The advisory covers waters both south of the Bay Bridge and the northern Bay, San Pablo Bay, Suisun Bay and the West Delta. The Weather Service says west winds of roughly 10 to 20 knots with gusts up to 25 knots can produce moderate chop and hazardous conditions for smaller vessels.
Conditions are stronger outside the Golden Gate. The nearshore coastal waters from Point Reyes to Pigeon Point remain under a Small Craft Advisory until 3 a.m. Sunday, with northwest winds around 10 to 20 knots and gusts up to 30 knots.
This is a marine hazard, not a severe-weather warning for the city
The distinction matters. People walking through San Francisco may experience an ordinary breezy afternoon while a small boat several miles away is dealing with much rougher conditions.
A Small Craft Advisory is aimed at mariners. The Weather Service warns that the combination of wind and waves can be hazardous, particularly for inexperienced operators and smaller vessels.
It does not mean San Francisco is under a severe wind warning on land, and it should not be read as one.
The strongest winds are outside the Bay
The Weather Service's marine discussion says fresh to strong northwest breezes are creating hazardous small-craft conditions along the Central California coast. The forecast is roughest around exposed coastal waters, with conditions expected to improve later Sunday and into early next week.
Inside the Bay, the advisory expires earlier Saturday night. Outside the Golden Gate, the nearshore Point Reyes-to-Pigeon Point zone remains covered into early Sunday morning.
For a boater leaving San Francisco, that difference can be important. The conditions seen at a marina inside the Bay are not necessarily the conditions encountered after passing under the Golden Gate Bridge.
Check the forecast again before departure
Marine advisories are short-lived and can be extended, replaced or canceled as observations change. Anyone planning to sail, fish, kayak or operate a smaller vessel Saturday evening should check the latest National Weather Service marine forecast immediately before departure.
SF News Today's live weather page provides the latest San Francisco forecast and Weather Service information, but marine users should rely on the current NWS marine product for the exact zone they plan to enter.
The useful takeaway for Saturday is straightforward: conditions can look benign from shore while still being hazardous for small craft on the Bay and substantially rougher outside the Golden Gate.