Overview

• A late‑winter heatwave running from September 18 to 22 is pushing temperatures toward or above 40°C across the Center‑West, North, Northeast and parts of the Southeast, with humidity in some interior areas dropping to 12–25%.
• An extratropical cyclone tied to a strong cold front is forecast to intensify over September 20–21 in Rio Grande do Sul, bringing heavy rain, hail and wind gusts that may exceed 100 km/h, along with hydrological risk.
• São Paulo is set for a hot weekend before a frontal passage late Sunday into Monday brings storms, potential hail and a sharp temperature drop, with forecasts indicating highs near 18°C early next week.
• Rio de Janeiro should approach 40°C this weekend, then see rain and a notable cooldown early in the week as a polar air mass advances, with Tuesday highs near 24°C projected.
• Officials advise avoiding exposure during storms, disconnecting electronics and monitoring slopes, while utilities flagged priority restoration for customers dependent on life‑support equipment; meteorologists say a developing La Niña could favor intermittent cold spells in spring.