A dawn at 28 degrees in Alto Alentejo
The dawn of September 4, 2026 broke national thermal records at the main IPMA weather station in Portalegre, reaching a minimum temperature of 28°C. This figure placed the municipality at the top of the extreme heat tables nationwide, significantly exceeding the usual climatological averages for the end of the summer season in the Alto Alentejo region, according to data released by the Portuguese Institute for Sea and Atmosphere (IPMA) in 2026.
This extreme episode is not an isolated case, being part of a heatwave driven by the circulation of an upper-level low-pressure system combined with an anticyclone centered over North Africa. The phenomenon transported very hot and dry air masses, laden with dust, into the Alentejo territory, maintaining consecutive tropical nights during the transition to the new astronomical season, as recorded by the IPMA in 2026.
The persistence of these anomalous thermal values led the Portuguese Institute for Sea and Atmosphere to issue and extend successive yellow warnings for hot weather, covering the district of Portalegre and prolonging the alerts until 6:00 PM on Wednesday, September 23, 2026, the date that marked the official beginning of autumn in the northern hemisphere.
The thermal anomaly and the September thermometer
The thermal impact on the municipality is clearly reflected in the consolidated monthly records. The average temperature for September 2026 in Portalegre presents a positive anomaly of a 2.1°C increase compared to the usual climatological reference values for the period, according to local meteorological data collected by AccuWeather in 2026.
This marked increase persisted over time, keeping official forecasts with maximums persistently above 30°C across the generally mainland territory, as pointed out by analyses released by Lusa News Agency and the IPMA in September 2026. The climate dynamics were reinforced by the influence of an anticyclone located north of the Azores and extending in a ridge to the Bay of Biscay, according to IPMA meteorological information from 2026.
To contextualize the severity of the episode on a national historical level, the absolute record for maximum temperature in September in mainland Portugal dates back to September 6, 2016, when Lousã reached 45°C, according to the IPMA's monthly historical records. Although Portalegre did not reach this absolute extreme of 2016, the persistence of high minimums such as the 23°C forecast by the IPMA for September 21, 2026 strangled the usual nighttime cooling during the transition to autumn.
The weight of heat on autumn crops and soil
In the agricultural sector of Alto Alentejo, the consequences of these prolonged heatwaves directly impact the productivity of annual and irrigated crops. According to reference agricultural forecasts published by Statistics Portugal (INE) in 2022, soil moisture scarcity during sensitive phases penalizes productive yields across the interior and south of the country in a generalized manner.
Academic analyses put forward by the Department of Phytotechnics of the University of Évora in 2022 demonstrate that anomalous temperatures during the summer and autumn transition periods severely compromise the proper establishment and root development of autumn-winter crops, threatening the germination of cereals and forages in the region.
Historically, the month of September in Alentejo marks the start of the grape harvest campaign and demands redoubled care with fruit orchards and olive groves. However, in 2025, the Office for Planning, Policies and General Administration (GPP) was already warning in its September statistical reports about the negative impact of prolonged water stress on these productive fringes essential to the regional economy.
Institutional response and water management
Faced with the pressure exerted on water resources and the need to safeguard irrigated farming, the Regional Directorate for Agriculture and Fisheries of Alentejo, currently integrated into the decentralized services of CCDR Alentejo in Portalegre, promoted technical training actions in 2026 focused strictly on the efficient use of irrigation water in scenarios of water scarcity.
Simultaneously, the Ministry of Agriculture made available in 2026 a global financial package of 40 million euros to support farmers affected by extreme weather events and climatic disturbances in various regions of the country, channeling funds through local decentralized services to mitigate income drops in the region.
These institutional measures align with long-term warnings drawn from climate adaptation projections, such as the scientific study Life Montado-Adapt published in 2017 for the RCP8.5 scenario, which predicts for the Alentejo territory an accumulated decrease in annual precipitation and the loss of up to 22 wet days per year by 2100, structurally worsening the pressure on autumn irrigation.
The expectation of the equinox and the reality on the ground
The most obvious reading pointed to the fact that, with the astronomical arrival of autumn on September 23, 2026, meteorological conditions would undergo automatic normalization, dissipating summer heat and easing agricultural management in the municipality of Portalegre, according to the cross-sectional analysis of the seasons.
However, IPMA data from September 2026 prove that the equinoctial transition failed to bring the expected thermal slowdown, with maximum temperatures continuing well above average and the positive anomaly of 2.1°C remaining active in local meteorological records, disproving the idea of immediate seasonal relief.
When this reading is tested against field reports from INE and the University of Évora, it appears that the critical factor is not just the date on the calendar, but rather the accumulation of thermal stress and soil dryness, which demonstrates that the structural difference felt in Alto Alentejo is not solved by a simple change of season.
The practical impact for those who farm the land
For the farmers of the municipality of Portalegre, these climate indicators of September 2026 translate into the daily need to anticipate rescue irrigation maneuvers, strictly managing the scarcity of available moisture in agricultural soils.
The persistence of tropical nights with 28°C and maximums permanently above 30°C forces producers to redouble operational costs with energy and groundwater abstraction, at a time when the soil should naturally recover after the end of summer.
This prolonged heat scenario has profoundly altered regional agricultural planning for coming years, shortening safety margins for the setting of crops and demanding structural adaptation to the new climatic conditions recorded by the IPMA.