Cascais weather in September

September in Cascais is high-20s C days with evenings that cool enough for a light jacket, and it is still beach season, with lifeguards and rentals running. Two Atlantic facts shape it. The sea peaks at about 20C here and never really gets warmer than that, so September is as good as it gets rather than warm. And the wind sorts the beaches: the small ones inside the town are sheltered, while Guincho, just outside and square on to the ocean, is where locals do not go when it blows. Sesimbra and Ericeira are the alternatives along the same coast. The record: 25C days, 18.2C nights, 3.2 precipitation days, 10.9 hours of sun, an 18.4C sea and a 22 kph wind.

Regulars are specific this counts as a genuine sunbathing month when conditions run normal, one visitor even describing early May as scorching and warm enough for paddling in the water despite how early in the season it is. Our row backs that mild, genuinely wet read, 21.9C over 15.3C nights feeling 13C, with 35mm of rain across 4.6 days and a real 23.8 kph wind. Regulars are consistent conditions here stay genuinely changeable rather than guaranteed, a sunny warm day and a cooler rainy one both realistic outcomes depending on exactly when a trip lands. The sea itself stays properly cold this early, well short of comfortable swimming temperatures for most visitors regardless of how warm the air gets. The sea sits at 16.5C. The record: 12.4 hours of sun, humidity 75 percent and AQI 48.

Cascais-forum threads on November weather call it right at the seasonal hinge: some visitors catch stretches close to beach weather, others land square in grey winter days, and the difference often comes down to which specific week a trip falls in. Posters describe overall luck with the weather as decent more often than not, rain expected but genuinely manageable around a normal sightseeing itinerary rather than a trip-ruiner. Regulars are consistent that swimming is off the table this late in the year - the water and air have both cooled enough that sunbathing and a proper swim no longer make sense, even on a warm afternoon. The clearest upside repeated across threads: the summer crowds are fully gone by November, giving the seaside promenade and old town a noticeably calmer, more local feel that many posters say they prefer to the peak-season version. The record: 18.2C days feeling like 17C, 13.4C nights, 81mm across 9.8 days, a 17.7C sea, 80 percent humidity and 7.5 hours of sun.

Cascais-forum threads on summer wind draw a useful distinction: the town's own small beaches aren't much bothered by it, but Guincho beach just outside town is exposed enough that locals skip it on a windy day - worth knowing before picking a beach based on the town center's calm. August itself is called the peak month for tourists, with the in-town beaches getting properly crowded, especially on weekends when Lisbon locals show up too. The record shows a cooler, breezier month than the sunny reputation implies: 26.5C days feeling like 28C, 18.8C nights, essentially none at all, a 15.9C sea on the cool side for swimming, 76 percent humidity and wind averaging 25 km/h - dry and sunny, but the Atlantic side of Portugal, not the Mediterranean.

June in Cascais is getting busier without being at its height - early dinners still get a table - and the thing regulars organise around is the wind. Flat calm is rare here and some wind is simply the norm, our row putting it at 24.4 kph. Their practical rule is geographic: it is not much of a problem in the town itself or on the small beaches inside it, but on a windy day locals do not go to Guincho, out beyond the edge of town and fully exposed. The water is the other caveat, under 20C on this coast in June - our row says 18.1C. Days can be warm and the nights are basically cool. The record: 23.6C days, 17C nights, 3.1 precipitation days carrying 9.7mm and 12.9 hours of sun.