**Trader consensus heavily favors 13°C as the lowest temperature recorded in São Paulo on September 17, 2026, reflecting observed minimums from official stations amid unusually cool and wet conditions.** Persistent cloud cover, record September rainfall, and advection of cooler air masses suppressed daytime heating and allowed overnight lows to reach this level, consistent with multiple forecast models and station reports showing nighttime readings near 13–14°C. This positioning aligns with the month’s departure from climatological norms, where enhanced precipitation and reduced solar radiation have produced below-average temperatures. A shift in the official measurement from the primary reference station—such as a revised reading of 12°C or 14°C due to microclimate variations or data adjustments—remains the primary scenario that could alter the outcome before final resolution.