**Recent forecasts from the National Weather Service and other models show San Francisco highs on September 4, 2026, centered in the upper 60s, with most guidance pointing to around 67°F under a returning marine layer after an early-season storm.** This places the daily maximum firmly in the 66–71°F range that dominates the market, with 70–71°F and 68–69°F together commanding over 70% of the implied probability. An unusually early September storm has driven temperatures 10–20°F below normal through Thursday, delivering light rain or drizzle and persistent cloud cover that suppressed daytime heating. As the front exits, gradual warming is expected Friday, but the classic marine layer—cool, moist air advected onshore by prevailing westerlies—will limit the rebound. Historical climatology supports this: the 1991–2020 average high for September 4 is 69.9°F, and recent years have frequently seen maxima in the mid-to-upper 60s when marine influence is strong. Key variables for traders include the precise timing of marine-layer clearance and any local microclimate differences across the city (e.g., warmer eastern neighborhoods versus cooler coastal zones). Updated model runs and the next NWS forecast discussion will likely refine the exact peak, keeping the 68–71°F outcomes as the clearest consensus while leaving room for modest upside or downside shifts.