Mainland Portugal experienced on September 3 the fourth hottest September day since 1941, with an average temperature of 27.61 degrees Celsius, according to data from the Portuguese Institute for the Sea and the Atmosphere (IPMA). The highest maximum temperature value was recorded in Alcochete, where thermometers reached 44.3 degrees Celsius. On September 4, Portalegre recorded a minimum temperature of 28 degrees Celsius, the highest minimum temperature observed during this heat episode.
The exceptionally high temperatures resulted from atmospheric circulation conditioned by the presence of a small depression, with upper-level expression, located southwest of mainland Portugal, combined with an anticyclone centered over North Africa and extended in a ridge to the Iberian Peninsula. This combination favored south and southeast flows and the transport of a very hot and dry air mass from North Africa, accompanied by a high concentration of dust.
The heat episode led to the surpassing of previous maximum temperature values for the month of September at 17% of the meteorological stations analyzed by IPMA. The previous highest minimum temperature values were also surpassed or equaled at eight meteorological stations.
Despite the values recorded in recent days, the absolute record for maximum temperature in September remains at 45 degrees Celsius, recorded on September 6, 2016, at the meteorological station in Lousã, in the district of Coimbra.