Portugal and northern Spain get lumped together with the rest of southern Europe on “best time to visit” advice, which usually means “avoid August” and not much else. For a route that actually crosses both – say, Lisbon through Porto, Santiago de Compostela, and San Sebastián – the timing question is more specific, because the two ends of the trip have different weather logic.
Lisbon and Porto: shoulder season over summer
Both cities are walkable-first destinations – Alfama’s hills, Porto’s riverside steps – and July/August heat makes that kind of walking genuinely unpleasant by early afternoon. May, June, September, and October all keep daytime temperatures in a range where a full day on foot doesn’t require retreating indoors from 1 to 4pm. October specifically also thins out the cruise-ship crowds that fill Porto’s riverside in peak summer.
Santiago de Compostela: less weather-sensitive
Galicia’s climate is wetter and cooler year-round than Portugal’s coast, which makes it comparatively weather-insensitive as a stop – it’s a reasonable add to a route in most months, including ones that would be too cool or wet for a coastal Portugal-only trip.
San Sebastián: the one city where summer has a real case
This is the exception. San Sebastián’s appeal leans heavily on Playa de la Concha and the beach culture around it, and that’s genuinely better in July/August than in October. The trade-off is pintxos-bar crowding and higher lodging cost at the same time. Early October is the compromise: beach weather usually still holds, and both crowding and price drop from peak.
The route-level answer
For a route that treats all four cities as roughly equal stops, early-to-mid October comes out ahead of peak summer on balance – it costs San Sebastián a few degrees of certainty on beach weather in exchange for a meaningfully better experience in Lisbon, Porto, and Santiago de Compostela. If San Sebastián’s beach is the actual priority for the trip, shift the whole route two to three weeks earlier and accept the trade-off in the other direction.
Want to see how a shift in dates changes the cost, not just the weather odds? Describe your dates to the planner and compare.