Traders assign the highest probabilities to a daily maximum between 19°C and 21°C in São Paulo on May 18, reflecting narrow uncertainty in the latest short-range model guidance. May brings the onset of autumn in the Southern Hemisphere, with typical highs declining toward the seasonal average of 22–23°C as cooler maritime air replaces lingering summer warmth. Current forecasts indicate stable high pressure, light winds, and only isolated showers that may limit daytime heating to the low 20s Celsius. Small variations in cloud cover or the timing of any weak frontal boundary over the next 48 hours remain the key variables that could shift the peak by 1–2°C.