Traders favor 17–19°C for São Paulo’s August 31 minimum as an approaching cold front begins eroding the current warm, dry air mass that produced highs near 34°C late in the month. Official guidance from Brazilian meteorological services and global models shows overnight radiative cooling under variable cloud cover competing with residual northerly flow, creating forecast spreads of roughly 18–21°C. Key uncertainties include exact frontal timing, low-level moisture, and wind speeds that modulate boundary-layer mixing. Updated model runs and INMET observations through the evening of August 30 will refine whether minimums dip toward the lower teens or hold near 20°C.