Friday, 21 August, is expected to remain largely dry across mainland Portugal. Some areas may start the day with cloud cover, but conditions should gradually clear, leaving plenty of sunshine. Temperatures will vary considerably across the country, with highs ranging from around 20°C in Viana do Castelo to 30°C in Castelo Branco.

Saturday should follow a similar pattern, with generally dry and stable weather and little change in temperatures. However, clouds are expected to begin building over northern Portugal during the afternoon before gradually spreading towards parts of the Centre, particularly along the coast.

The bigger change is expected on Sunday, 23 August, as an Atlantic depression approaches mainland Portugal.

Cloud cover

Weather forecasts reported by Executive Digest point to increasing cloud cover and humidity from the early hours of Sunday, followed by rain later in the day.

Rain is expected to reach the coast between Caldas da Rainha and Lisbon from around midday, where some periods of heavier precipitation could occur. The unsettled weather is then forecast to reach the Setúbal district from around 2pm before spreading to other parts of mainland Portugal during the afternoon and evening.

Conditions could deteriorate further on Monday, 24 August, when rain is forecast across a much larger part of the country. Stronger winds and increasingly rough sea conditions are also expected as the low-pressure system moves northeast across the Iberian Peninsula.

Forecast uncertainty

The Portuguese Institute for Sea and Atmosphere (IPMA) currently shows no weather warnings for mainland districts for the period displayed, although forecasts can change as the depression approaches. IPMA also notes that numerical forecasts carry greater uncertainty when predicting extreme rainfall and wind events.

For now, the weekend is expected to begin with relatively calm summer weather before becoming noticeably wetter and more unsettled from Sunday onwards.