Portugal faces a significant weather change, with severe thunderstorms forecast for Saturday, September 5. According to Meteored Portugal, more than 12 lightning strikes per square kilometre may fall in some areas, especially in the North and Central regions. The storms will be accompanied by locally intense showers, hail, and strong wind gusts. The first convective cells may develop during the morning, including in coastal areas, with Lisbon and Leiria among the regions affected early on.
Before this change, Portugal will be under the influence of a very hot air mass. On Thursday, some locations in the Alentejo may register maximum temperatures above 40°C, possibly one of the hottest days of this period. High pressure systems act as a barrier that prevents Atlantic depressions and fronts from reaching the mainland. On Friday, the first signs of change begin to appear, with increased cloud cover and the possibility of occasional light precipitation.
The combination of high surface temperatures and colder air at altitude favours the rapid development of storm clouds. However, this is a multi-day forecast, so the exact location and intensity of the phenomena may still change. The instability forecast for Saturday may be relatively short-lived.
After the thunderstorm episode, the NAO+ pattern is expected to regain strength between September 7 and 10, deflecting Atlantic depressions and fronts to higher latitudes. The ECMWF sub-seasonal maps for the week of September 7 to 14 indicate positive temperature anomalies across almost all of mainland Portugal, with the heat signal most evident in the South and in the interior of the North and Central regions. As for precipitation, negative anomalies are expected, which means that despite the potentially unstable Saturday, the trend for the first half of September is for warmer and drier conditions than usual.
