Het weer in Bilbao (Guggenheim) in december

Regulars call this normally the driest month of the year here on paper, warm and agreeable in the mid-to-late 20s Celsius, while being honest that the Atlantic coast setting means rain can still arrive any time regardless of the seasonal odds. Our row backs that warm, genuinely humid read, 27.4C reading as a hot 29C, over 16.9C nights, with 54mm of rain across 7.5 days and humidity at 80 percent. Regulars are consistent that a rain layer belongs in the bag even on what looks like a reliably warm week, since the region's unpredictability doesn't fully disappear even in its best month. The sea sits at a swimmable 22.9C, a real highlight for anyone splitting time with San Sebastian's beaches. The record: 11.1 hours of sun, a 15.8 kph wind and AQI 41.

Regulars call this a warm, not especially rainy month by local standards, with nights cool enough by evening that a light jacket comes out from around nine o'clock. Our row backs the warmth, 25.5C reading as 26C over 14.5C nights, though rain is a real presence at 93.4mm across 10.1 days - clashing winds off the Atlantic make this coast's weather genuinely hard to predict even in a normally dry month. Their honest local habit is the useful detail: people are out in rain gear regardless, and the streets stay packed whatever the sky is doing, so a shower here is rarely a reason to change plans. Inland spots like Rioja and Laguardia can run warmer and drier than the coast on the same day. The sea holds 22.2C. The record: humidity 79 percent, 9.6 hours of sun, a 16.1 kph wind and AQI 39.

Regulars rate June above May here and give the reason as instability rather than cold: May swings, and when it rains it can be the sirimiri - the slow, fine, long-lasting drizzle this coast is named for - or ordinary showers, or a thunderstorm, and they say plainly that it is hard to call. Our row reads 21.6C days over 11.3C nights with 74.8mm across 11.2 days, and a sea at 16.6C that matches their 16 to 18C and rules out swimming for most. They add a note on the long view: the month-long unbroken rains this region was known for no longer happen. The record: humidity 81 percent, 10.8 hours of sun inside 14.7 of daylight, and AQI 42.

June in Bilbao is sunny and warm and a raincoat is still advisable, which regulars explain with a local figure rather than an average: the city records rain on something like 185 days a year and has no dry month at all, though June itself takes only about five of those wet days. Our row gives 78.2mm across 10.2 precipitation days under 24.5C, and the 83 percent humidity is the Basque coast showing through. The word to know is sirimiri - a slow, fine, long-lasting drizzle rather than a downpour, the same thing San Sebastian regulars warn about - and it is why a hood beats an umbrella here. The record: 15C nights, feels-like 26C, 10.7 hours of sun, a 20.4C sea and AQI 43.