**The market-implied odds strongly favor 15°C as the lowest temperature recorded in São Paulo on September 4, 2026, reflecting trader consensus anchored in official observational data.** Early September in the region typically features cooling from the approach of a frontal system, with overnight radiative cooling under clearer skies allowing minimums to dip into the mid-teens Celsius. Multiple meteorological sources, including forecasts from sites tracking Congonhas Airport and regional models, converged on a daily minimum of 15°C (or very close), with daytime highs near 26°C. This alignment between pre-event model runs, real-time station readings, and post-event verification created near-certainty once the 24-hour period closed. The 99% probability on 15°C indicates skin-in-the-game confidence that the official minimum—likely from INMET or airport networks—settled precisely at that threshold rather than 14°C or 16°C. Minor model spreads or microclimate variations between urban stations could theoretically shift the recorded low by 1°C, but consistent reports across sources made such outcomes improbable. Upcoming resolution hinges on the final official daily summary, with no major data revisions expected given the stability of observations.