This study aims to investigate the atmospheric conditions and human thermal comfort related to extreme heat in Rio de Janeiro during the first quarter of 2024. The dataset includes meteorological data from the A636-Jacarepaguá station of INMET and seven stations from the Alerta Rio system. Weather types were classified using principal components analysis (PCA) and cluster analysis (CA). Additionally, three thermal comfort indices were calculated: the heat index (HI), physiologically equivalent temperature (PET), and modified PET (mPET). Five groups of surface weather types were identified, with two being more frequent and associated with extreme heat events. These two groups accounted for over 70% of the days in all months. Critical thermal sensation values were found, particularly at the Guaratiba station, where the daytime HI exceeded 60 °C, and at the Riocentro station, where the nighttime HI surpassed 40 °C. The HI showed a greater range and variability compared with the PET and mPET, highlighting the importance of investigating microclimatic factors which intensify urban heat in central and coastal areas and cause daytime overheating in more distant regions like Guaratiba. This study emphasizes the need for detailed investigation into microclimatic factors and their public health implications, especially in areas with high tourist activity and vulnerable populations.