Don't trust the little cloud icon on your iPhone. Honestly, if you're planning a trip to the Basque Country and you're staring at a generic weather app, you're setting yourself up for a very confusing afternoon. San Sebastian—or Donostia, as we locals call it—doesn't follow the rules of standard meteorology. It’s tucked right between the Cantabrian Sea and the literal wall of the Pyrenees. This creates a microclimate that is, frankly, a bit of a nightmare for algorithms but a dream for anyone who likes dramatic scenery.
A weather forecast San Sebastian can change in the time it takes you to eat a single gilda at a pintxo bar. You might start your morning at La Concha beach under a sky so blue it looks photoshopped, and by 2:00 PM, you’re sprinting for cover as a galerna—a sudden, violent coastal gale—rips through the bay. This isn't just "changeable" weather. It’s a specific atmospheric personality.
The Sirimiri Factor and Why You’ll Get Wet Anyway
In most parts of the world, it either rains or it doesn't. In San Sebastian, we have the sirimiri. It’s not quite rain, but it’s definitely not mist. It’s a fine, persistent drizzle that seems to defy gravity, hanging in the air until it eventually soaks through even the "waterproof" jacket you bought specifically for this trip.
Standard weather apps often struggle with this. They’ll show a 10% chance of precipitation because there’s no massive storm system moving in, but you’ll spend the whole day damp. The sirimiri is caused by the humid Atlantic air getting trapped against the mountains. It cools, it condenses, and it falls—slowly. If you see a weather forecast San Sebastian that predicts "mostly cloudy," go ahead and assume the sirimiri is coming for you.
It’s actually quite beautiful once you stop fighting it. The city takes on a soft, silvery glow. The stones of the Old Town (Parte Vieja) start to shine. There’s a reason the Basque Country is so impossibly green; this constant, gentle watering is the secret sauce. But if you're a photographer, this light is a nightmare. Or a gift. It depends on how much you like moody, cinematic shadows.
Understanding the Bay’s Mood Swings
The geography here is the real culprit. You have Monte Igueldo on one side and Monte Urgull on the other, framing the bay. This creates a funnel. When the wind kicks up from the northwest, it brings the "maritimo" influence—cool, wet, and salty. But if the wind shifts south? Everything changes.
The Surada is a warm, dry wind that comes off the land. It can spike temperatures by ten degrees in an hour. I’ve seen days in November where the weather forecast San Sebastian suggested a chilly 12°C, only for a southern wind to blow in and push us up to a balmy 22°C. People start shedding layers, the terraces fill up, and suddenly it feels like summer in the middle of autumn. Then, as soon as the wind dies down or shifts back to the sea, the temperature crashes. It’s erratic. It’s temperamental. It’s Donostia.
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When to Actually Visit (If You Hate Rain)
If you're looking for the most stable weather forecast San Sebastian can offer, you’re looking at July and August. But here's the catch: so is everyone else. The city gets packed.
September is arguably the "sweet spot." The Atlantic has warmed up all summer, so the water is at its peak temperature—around 20°C to 21°C. The fierce heat of the Spanish interior starts to bleed over the mountains, but the coastal breeze keeps it from feeling oppressive. Statistically, September has fewer rainy days than May or June.
- Spring (March–May): Deeply unpredictable. You will see four seasons in one day. Great for seeing the waterfalls in the nearby hills, but pack a sturdy umbrella. Not the cheap ones from the gift shop; the wind will snap those in seconds.
- Summer (June–August): Warm, rarely "hot" like Seville or Madrid. Expect 22-26°C. Perfect for surfing at Zurriola.
- Autumn (September–November): My personal favorite. The light turns golden, the crowds thin out, and the surf gets world-class.
- Winter (December–February): Grey. Very grey. But the storms hitting the Peine del Viento (Comb of the Wind) sculpture are a sight you have to see once in your life.
The Science of the Galerna
You need to know about the galerna. This is a weather phenomenon unique to the Bay of Biscay. It usually happens on hot days. The pressure drops, the wind suddenly flips to the northwest, and the temperature plummets—sometimes dropping 10°C in just a few minutes.
The wind speeds can hit 100 km/h. If you’re at the beach and you notice the horizon suddenly turning a dark, bruised purple and the wind shifting from a warm breeze to a cold gust, leave. Immediately. Don’t wait for the rain. The weather forecast San Sebastian might not even mention it until it’s happening because they are notoriously hard to predict more than an hour or two out.
Local Secrets for Checking the Forecast
Stop using the default weather app on your phone. It pulls data from global models like the GFS (Global Forecast System), which are great for large landmasses but terrible for coastal microclimates.
Instead, look at Euskalmet. This is the Basque Meteorology Agency. They have local weather stations all over the province of Gipuzkoa. Their radar is significantly more accurate for San Sebastian because they understand how the mountains interact with the sea. If Euskalmet says it’s going to rain at 4:00 PM, you can bet your life it will start at 3:55 PM.
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Another trick? Look at the mountains. If Monte Igueldo has a "hat" of clouds, the weather is going to stay messy. If the clouds are high and wispy, you're usually clear for a few hours.
Dressing for the "Donostia Layer"
Forget fashion for a second. If you want to survive the weather forecast San Sebastian quirks, you need to master the art of the layer.
Even in mid-July, the evenings can get brisk. The sea breeze doesn't care that you spent the day sweating. You'll see locals carrying a light knit sweater or a "gabardina" (trench coat) even when the sun is out. It's not a fashion statement; it's a survival tactic.
The footwear situation is also critical. The sidewalks in the Centro and the Old Town are made of stone that becomes incredibly slick when wet. Fashionable leather-soled shoes are basically ice skates here. Wear something with grip. You’ll thank me when you aren't sliding across the Plaza de la Constitución.
The "Sea State" Matters More Than You Think
If you're here for the beach or surfing, the weather forecast San Sebastian is only half the story. You need to check the tide tables and the swell.
La Concha beach virtually disappears at high tide. If you plan a beach day based purely on "sunny" weather and arrive at peak high tide, you'll be sitting on a concrete wall rather than sand. Conversely, the Zurriola beach (the surfer's beach) gets massive during a northern swell. Even if the sun is shining, the red flags will be up if the Atlantic is angry.
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The local life revolves around the water. We watch the tides like people in other cities watch the traffic. A "low tide" afternoon in the summer is the peak social hour.
Why the Rain Makes the Food Better
There’s a local theory that the temperamental weather forecast San Sebastian is why the food is so good. When it rains, you go inside. When you go inside, you eat.
The Basque "Sociedades Gastronómicas" (private cooking clubs) were built as refuges from the weather. The pintxo culture thrives because it’s a perfect indoor-outdoor hybrid; you pop in for a bite, wait for a shower to pass, then move to the next spot.
If the forecast looks dismal, don't cancel your trip. Some of my best memories in this city involve being tucked into a corner of a bar like Ganbara or Txepetxa, listening to the rain hammer against the shutters while eating a plate of wild mushrooms or anchovies. There is a specific kind of coziness—the Basques call it gozo—that you only get when the weather outside is doing its worst.
Navigating the "Basque Grey"
The sky can stay a flat, matte grey for days on end. This is the "Basque Grey." It’s not necessarily depressing; it’s more of a mood. It makes the colors of the city—the white railings of the promenade, the blue of the sea—pop in a way they don't in harsh sunlight.
Professional film crews actually love this light. It’s a giant natural softbox. If you see a weather forecast San Sebastian showing five days of clouds, don't despair. Your photos will actually have better detail and fewer harsh shadows than if it were blindingly sunny.
Actionable Steps for Your Visit
To truly master the local climate, you need a different approach than you’d use for a trip to the Mediterranean. Don’t let the maps fool you.
- Download the Euskalmet App: Delete the generic ones. Euskalmet is the gold standard for accuracy in the Basque Country.
- Check the Tide Charts: Use a site like "Magicseaweed" or "Surfline" to see when La Concha beach will actually exist.
- Invest in a "Windproof" Umbrella: Or better yet, a high-quality raincoat with a hood. Umbrellas are often useless against the coastal gusts.
- Embrace the Morning: In the summer, the clouds often burn off by midday. If you wake up and it’s grey, don't go back to sleep. Usually, by the time you've finished your café con leche, the sun will be breaking through.
- Watch the "Peine del Viento": If the forecast calls for a storm, head to the end of Ondarreta beach. The interaction between the waves and Eduardo Chillida's sculptures is the best free show in the city.
- Always Carry a "Just in Case" Layer: Even if it's 28°C at noon, bring a light jacket if you're staying out for dinner. The temperature drop once the sun goes down over the Atlantic is real.
San Sebastian is one of the most beautiful cities on earth precisely because of its weather, not in spite of it. The rain, the wind, and the sudden bursts of heat are what shaped this landscape and this culture. Once you stop checking the weather forecast San Sebastian every five minutes and just learn to roll with the sirimiri, you’ll finally start to see the city for what it really is. A place that’s always changing, always green, and always ready for the next glass of txakoli, rain or shine.