Nine Districts Go Under a Yellow Heat Warning at Ten on Saturday Morning, and Four Northern Ones Join Them for Sunday Only
IPMA cites the persistence of high maximum temperatures. Evora is forecast at 37.9 degrees on Sunday, Lisbon at 36.4, and Lisbon's overnight minimum climbs from 17.5 to 21.2 across the weekend.
The Instituto Português do Mar e da Atmosfera has placed nine districts of central and southern mainland Portugal under a yellow warning for heat this weekend, and will add four northern districts on Sunday. The stated reason is the persistence of high maximum temperatures rather than any single extreme peak.
Évora, Santarém, Setúbal, Lisboa, Leiria, Beja, Castelo Branco, Coimbra and Portalegre are under warning from 10:00 on Saturday until 17:00 on Sunday. Braga, Aveiro, Viana do Castelo and Porto are under warning on Sunday only, between 10:00 and 17:00.
What Yellow Means
Yellow is the least serious of the three warning levels IPMA issues, below orange and red. It is not a statement that the weather is dangerous to the general population. It is issued when conditions present a risk to particular activities that depend on the weather, which in practice means outdoor work, sport, and anything involving people who are already vulnerable to heat.
The distinction matters because a yellow heat warning in September reads differently from the same warning in July. The national heat-health response draws on the same forecasts, and the groups it names are consistent: people over 65, infants, those with cardiovascular or respiratory conditions, and anyone working outdoors through the middle of the day.
The Numbers Behind the Warning
IPMA's own city forecasts show where the weekend is heading. Évora is forecast to reach 37.3 degrees on Saturday and 37.9 on Sunday. Beja goes to 36.8 and then 37.1, Santarém to 36.7 and 37.2. Lisbon is forecast at 36.0 on Saturday and 36.4 on Sunday, against 32.9 on Friday.
Coimbra makes the largest single jump, from 29.9 on Friday to 35.1 on Saturday and 36.3 on Sunday. Leiria moves from 28.1 to 33.9 and then 35.8. Portalegre reaches 35.1 and 36.1, Castelo Branco 34.8 and 35.4, Setúbal 35.2 and then 34.5, the one district forecast to ease slightly on the second day.
The north explains why its warning starts a day later. Porto sits at 25.7 degrees on Friday, climbs to 30.9 on Saturday and 31.4 on Sunday. The heat arrives there as the weekend ends rather than as it begins.
Overnight minima are the part of a heat episode that tends to get overlooked, and they are rising too. Lisbon's forecast minimum goes from 17.5 on Friday to 21.2 by Sunday, and Portalegre's from 19.8 to 24.2. A night that does not drop below the low twenties gives a building, and a body, no chance to shed the previous day's heat, which is the mechanism behind most of the excess mortality recorded in heat episodes.
Fire Risk, in Context
Heat of this kind in September lands on vegetation that has had a full summer to dry. It is worth keeping the season's overall picture in view: Portugal's burnt area this year is down by roughly three quarters, and as we reported when a fire specialist assessed the reason, the credit belongs mainly to the weather rather than to any change in policy. A hot, dry weekend is precisely the weather that has been absent.
Practical advice is unchanged and unglamorous: drink water without waiting to feel thirsty, keep shutters closed through the afternoon and ventilate at night, avoid physical effort between 11:00 and 17:00, never leave a person or an animal in a parked car, and check on older neighbours living alone. Warnings are updated twice daily on the IPMA website, and the district-level detail can shift as the weekend approaches.
