Trader consensus centers on 70–73°F for San Francisco’s highest temperature on September 18, reflecting model guidance showing mild conditions under a persistent marine layer and moderate onshore flow from the Pacific. Typical September highs average near 71°F, with sea breezes and coastal stratus limiting afternoon warming despite seasonal solar input. Recent forecasts from operational models indicate highs in the upper 60s to low 70s, with minimal warming expected from any offshore flow or clear-sky periods. Key variables include the depth of the marine inversion and wind direction shifts that could allow brief inland heating. Updated National Weather Service guidance and morning soundings will refine these ranges ahead of the 24-hour observation window used for market resolution.