According to the weather forecast analyzed by Luso Meteo, September in Portugal could begin with several days of dry weather and high temperatures, with very high values possibly reached between the 3rd and 5th in the regions that are usually warmest. In the first days of the month, rain should remain practically away from mainland Portugal, although from the first weekend onwards there may be the first signs of a change in the atmospheric pattern, with the possibility of showers or thunderstorms in some regions.
During the second week, the atmospheric circulation may begin to undergo new changes, especially if the anticyclone moves to higher latitudes. This configuration would open more space in the Atlantic for disturbance circulation, although a prolonged period of rain is not expected at this stage. IPMA does not currently indicate above-normal precipitation for this week.
It is mainly after mid-September that the meteorological evolution becomes more interesting, with signs in the models of a possible more profound change in the Atlantic circulation that could favor the approach of depressions and frontal systems to the Iberian Peninsula. The evolution of the Madden-Julian Oscillation is one of the elements being monitored, and it could contribute to a configuration more favorable to a negative NAO regime.
The last ten days of September appear as the period that deserves the most attention, with a greater possibility of frontal passages and depressions accompanied by periods of rain, wind and dropping temperatures. The North and Central regions will naturally be among the most exposed to the passage of frontal systems, while in the Azores the signal for above-normal precipitation is already forecast for the first weeks of the month, according to IPMA.
