Recent ensemble forecasts from Brazil’s INMET/CPTEC and the ECMWF/GFS models converge on a daily maximum of 19–21 °C for São Paulo on May 18, reflecting the city’s typical late-autumn pattern of reduced solar heating and frequent passage of weak cold fronts. Light surface winds, moderate humidity near 70 %, and partly cloudy skies are expected to limit afternoon warming, while the absence of a strong subtropical ridge keeps temperatures from climbing into the mid-20s. Traders assign the highest probabilities to the 19–21 °C bins because small shifts in frontal timing or cloud cover within the next 48 hours could easily move the observed high by 1–2 °C. Official resolution will rely on calibrated readings from São Paulo-Guarulhos International Airport, with the final bulletin expected shortly after 18:00 local time on May 18.