We are entering the peak window for summer thunderstorms in Mallorca and I thought it worth sharing some observations after nearly thirty years of watching them develop.
The pattern is usually the same. A hot, still morning with hazy skies. By midday you start to see cumulus building over the Serra de Tramuntana — big white towers that look harmless enough. If they keep growing vertically and the tops start to flatten out into that anvil shape, you have maybe two hours before things get interesting. The storms tend to build inland first and then roll south or southeast towards the coast in the late afternoon.
What catches people out is the speed. You can go from flat calm to 35 knots of wind in fifteen minutes, with visibility dropping to almost nothing in heavy rain. I was caught in one off Cap Enderrocat three years ago and the gusts hit 45 knots — proper survival conditions for a small boat.
My rule is simple: if I can see towering cumulus over the mountains by 11am and the AEMET forecast mentions any chance of tormentas, I either stay close to port or make sure I have a bolt hole within thirty minutes sailing. The Predicción Marítima on the AEMET website is very reliable for this — check it every morning before you go out.
Anyone else been caught out by one of these? They are genuinely dramatic when they arrive.
Carlos, excellent summary as always. The anvil formation over the Tramuntana is the big clue and you have described it perfectly.
One thing I would add from a practical standpoint — if you are out sailing and you see those towers building, pay attention to whether the cloud base is darkening underneath. That grey-purple colour at the base means the updraft has enough moisture to produce heavy rain and probably electrical activity. At that point you want to be thinking about where you can get to in the next hour, not the next two.
I got caught out properly last August somewhere between Sóller and Sa Calobra. Beautiful morning, had the cruising chute up, everything lovely. Spotted the buildup over the mountains around 1300 but thought I had plenty of time. Within forty minutes the wind went from a gentle F3 to a solid F7 from the northwest, the rain was horizontal, and I was trying to get the chute down in conditions I really should not have had it up in. Lesson learned — when in doubt, get the canvas off early. You can always put it back up.
The barometric pressure drop is the other reliable indicator. If your barometer shows a sharp fall of 3-4 millibars in an hour during an otherwise settled spell, something is coming and it is coming fast.
Carlos and James have covered the forecasting side really well. From my side as someone who takes charter crews out in this weather, the thing I drill into every briefing at this time of year is: have a plan B anchorage that is closer than your destination.
Last week I had a crew doing the south coast route towards Colònia de Sant Jordi. Beautiful morning, not a cloud. By 1400 the Tramuntana was stacking up exactly as Carlos described and we had a proper cell moving south fast. We ducked into Cala Pi with maybe 30 minutes to spare before it hit. Twenty minutes of absolute chaos — 40-knot gusts, horizontal rain, lightning close enough to feel it — and then blue sky again like nothing happened.
The crew were shaken but safe because we had already identified Cala Pi as our bolt-hole before we left. If you are sailing the south coast in August, know where your nearest shelter is at every point along the route. Portals Vells, Cala Pi, Cala Llombards — have them on your plotter and ready to go.
This is really helpful timing — I have been absolutely dreading getting caught in one of these. Last Thursday I was walking along the Paseo Marítimo after work and watched one of those cells roll in from the mountains. The wind just switched on like someone had flipped a switch and within about ten minutes the boats in the marina were hobby-horsing all over the place. Genuinely scary to watch from shore, cannot imagine being out in it.
Katrin, your point about having a plan B anchorage closer than your destination is going straight into my notes. I think as a relatively new sailor my instinct would be to just keep going and try to outrun it, which from what you and Carlos are saying is exactly the wrong call. How far in advance do you typically make the call to divert? Is there a rule of thumb or is it just experience?
Sophie, to answer your question from earlier — yes, they can come on very fast. Last August I was anchored at Cala Figuera on the south coast and had about fifteen minutes between the first gust and full-on horizontal rain with lightning striking the cliffs. Longest fifteen minutes of my life getting the anchor up.
One practical tip nobody has mentioned yet — disconnect your VHF antenna from the backstay if you have a backstay-mounted aerial and you see lightning approaching. A direct strike to a backstay antenna will fry your entire electronics suite. I carry a short jumper cable so I can switch to a handheld VHF if needed. Paranoid maybe, but replacing a B&G system costs rather more than a bit of cable.
Reading all of this with wide eyes. We had a brief on thunderstorms during our Competent Crew session last week and the instructor basically said “if you see the anvil, you are already late.” But I was not entirely sure what an anvil cloud looks like versus just a normal big cloud? Carlos, your description helps a lot actually.
Also — is there a particular weather app you all use to check before going out? My instructor mentioned Windy but I have about six different apps on my phone now and they all seem to say slightly different things. I keep checking them all which probably makes it worse!
Quick update — we had a proper cell come through yesterday evening around 19:00. I was tied up in the Club de Mar and watched it build over the Tramuntana exactly as I described earlier in this thread. The whole sequence took about three hours from first cumulus to full anvil. Wind went from calm to 28 knots in the marina within maybe ten minutes, rain so heavy you could not see across to the cathedral.
The interesting thing was the timing. Usually these August storms hit mid to late afternoon but this one held off until early evening. I think the light northwesterly we had during the day delayed the thermal trigger. Worth noting because it means you cannot always rely on “if it has not happened by 17:00 you are fine” — that rule of thumb does not work every time.
Carlos, just saw your update about that cell on Thursday evening — I was actually walking home from work along the Paseo when it hit and got absolutely drenched. The wind came out of nowhere. Honestly it was like someone turned on a fire hose.
Anna, to answer your question about apps — I have been using Windy and it is brilliant for seeing the storm cells move in real time. The radar overlay shows you exactly where the rain is and which direction it is heading. Free version does everything you need.
Sophie, thank you so much for the Windy recommendation! I downloaded it after your post and spent about an hour just playing with the different layers. The radar overlay is brilliant — I can actually see the rain moving across the island in real time. Much better than the basic weather app I was using before.
I showed it to my husband and now he checks it every morning before we even have coffee. He is not a sailor but he has become obsessed with the wind arrows.
Anna, glad you are finding Windy useful. Tell your husband to look at the sounding charts too — once you learn to read the CAPE values you can predict afternoon storms before any cloud has even formed. High CAPE over the Tramuntana in the morning means almost guaranteed fireworks by evening.
We had another small cell pass through last night around 21:00, much weaker than the one last week. Barely 15 knots in the marina but some good lightning over Cap Blanc. The pattern this August has been very consistent — a few days of building heat, then a release. I would expect another strong one early next week if this calor keeps up.