Heat Wave Sets December Records in São Paulo as Rio Hits 40°C

Overview

• Brazil’s Inmet maintains an orange danger alert for a heat wave across eight states through Friday evening, covering the entire Southeast and parts of neighboring regions.
• São Paulo reached 35.9°C at the Mirante de Santana station on December 25, the city’s highest December reading in the historical series, and the hottest day of 2025.
• Rio de Janeiro registered around 40.1°C at the Guaratiba station and remains at Calor 3, the city’s third heat protocol level indicating sustained high temperatures.
• Public health impacts mounted as Rio’s municipal network recorded nearly 1,000 heat-related attendances over two days and the state health authority flagged 22 municipalities for excess heat from light to extreme.
• Utilities in Greater São Paulo reported a surge in water use with localized supply constraints, while forecasts from Alerta Rio, Inmet and Climatempo point to hot, dry conditions through the weekend before gradual easing.