Portugal’s national meteorological institute IPMA issued a yellow heat alert for nine mainland districts around 18 September 2026, as a late-season warm air mass pushed temperatures well above the seasonal average across much of the north and centre of the country.
Which Districts Are Under Alert
The yellow alert covered: Porto, Braga, Viana do Castelo, Bragança, Guarda, Viseu, Coimbra, Aveiro, and Vila Real — effectively the entire northern and central interior of mainland Portugal. Under IPMA’s colour-coded system, a yellow alert indicates conditions that may pose a health risk, particularly for older visitors and those with underlying health conditions.
Maximum temperatures in affected areas climbed to 36–40°C during peak alert days, roughly 8–10°C above the long-term average for mid-September. Lisbon and the Algarve were not included in this particular advisory.
What This Means for Visitors
Late September heat in northern Portugal is unusual but not unprecedented. Here’s how to stay comfortable:
- Hydration: Drink water regularly, even if you don’t feel thirsty. Cafés along most walking routes will fill a water bottle on request.
- Midday hours: Avoid extended outdoor activity between 12:00 and 16:00, when heat peaks. Major museums and covered markets are good alternatives.
- Footwear: Cobblestone and granite surfaces in historic centres absorb significant heat — closed-toe shoes with insoles are more comfortable than sandals on long walking days.
- Air conditioning: Many guesthouses in Porto’s older neighbourhoods do not have full air conditioning. If this matters to you, confirm before booking.
Cooling Off in the Affected Cities
Despite the heat, Porto remains very walkable in the early morning and evening. The Douro riverfront provides a breeze, and the wine cellars of Vila Nova de Gaia — built into hillsides — are kept naturally cool. In Coimbra, the university library and covered arcade of the old city offer shade throughout the day.
Looking Ahead
IPMA updates its alerts daily. By late September, Atlantic weather systems typically reassert control over northern Portugal, bringing temperatures back to the mid-20s. Travellers visiting in early October are unlikely to encounter the same conditions.
For a full breakdown of what to expect each month — including the best and worst times to visit — see our guide to the best time to visit Portugal. If you’re heading to Porto specifically, our city guide covers the seasonal patterns in detail. Travellers in affected districts should also check that their travel insurance for Portugal covers heat-related medical incidents.