Trader consensus on the 66–69°F range for San Francisco’s August 13 high reflects the strong influence of a persistent marine layer and onshore southwest flow, which have kept coastal temperatures suppressed despite warmer inland conditions. National Weather Service forecasts and recent model guidance indicate partly cloudy skies with highs likely peaking in the mid-to-upper 60s as sea breezes strengthen midday, limiting solar heating. This aligns with typical August climatology near 70°F but tempered by current coastal flood advisories and stable atmospheric conditions that reduce the chance of significant warming. Updated NWS briefings and afternoon model runs will be key inputs as traders assess any late-day clearing.