This article is a case study to analyze the synoptic and climatological aspects of an heat wave in Rio de Janeiro, located in the Southeast Region of Brazil, during November 2023. This work aims to investigate whether the high temperatures recorded on November 17 and 18, 2023, during a concert of an American singer, could be considered an extreme weather event. On the first day of the concert, the 17th, many people fell ill due to the extreme heat, and a 23-year-old female died, a victim of cardiorespiratory arrest caused by thermal exhaustion. On November 18, 11 meteorological stations recorded a maximum temperature (TX) equal to or over 40 °C, and the highest TX in the city was 43.5 °C. At a station located in the coldest area of the city, the highest TX (39.6ºC) in its entire historical record (1967-2023) was also recorded on the 18th. Such extremely high temperatures occurred during a prefrontal situation and at the end of a heat wave that lasted eight days. Analysis of the diurnal cycle of the air temperature on the 17th and 18th indicated that the minimum temperature (TN) was about 5 to 6 °C above its climatology; the TX was approximately 13 °C above its climatological value, and high temperatures lasted all afternoon. On the 18th, the Heat Index reached 55.1 ºC at 14:00 and 15:00 LT, characterizing a state of medical emergency during seven hours. In terms of climate, in addition to the increase in intensity and frequency of warm extremes over the city, the El Niño phenomenon (EN) was configured in the Pacific Ocean from April 2023 to May 2024, causing a drier and warmer spring in Southeast Brazil. This concert represented a milestone for the city regarding the need for local public policies to regulate massive crowd-gathering events during heat wave episodes. Finally, it is possible to state that the event was extreme, caused by the combination of a heat wave, in a prefrontal situation, during an EN event, and in a context of climate change.
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