- I've never seen anything like it before so I was very surprised. It lasted for almost ten minutes until it came down to the water and it was very large, he says.

According to SVT's meteorologist, it is neither unusual nor common for thrombus in weather conditions like these.

- They are always created from the underside of a heavy cloud, usually in heavy rain or thunderstorms. They usually show up in late summer when it is relatively warm and humid and when the seawater is heated, says meteorologist Per Stenborg.

Tilda and Clara Svärd write: “Around 18, we were down on the beach in Borgehage on Öland and saw a drum in Kalmarsund. It was big and it sprayed a lot of water! ”Photo: Tilda Svärd

Can be powerful

This particular thromb passed without causing any damage, but they are not always harmless.

- They can be really powerful right when they pass, but they are very narrow. Of course, if they are out at sea, boats should not be nearby. These are enormous forces, ”says Per Stenborg.

See viewers' pictures of the thrombus:

Peter Ekfeldt caught the drum on a picture from Strand hotel in Borgholm. Photo: Peter Ekfeldt

Cecilia Månsson took this picture of how people who bathed in Köpingsvik witnessed the weather phenomenon. Photo: Cecilia Månsson

Hanna Irenaeus, 14 years old, took this picture from Öland. Photo: Hanna Irenaeus

Linda Karlgren caught the trombone in the photo as she crossed the coast road from Timmernabben towards Mönsterås. “We saw it for about 10 minutes. It also thundered and flashed, ”she writes. Photo: Linda Karlgren

Simon Zachrisson was having dinner in Timmernabben when he saw the trombone go over Oknö. Photo: Simon Zachrisson