An unusually warm Mediterranean Sea helped provide the moisture and energy behind a powerful early-October storm that brought torrential rain, thunderstorms and flooding to Ibiza and the wider Balearic Islands.

The episode arrived after an exceptionally warm summer for Spanish waters, with several monitoring stations recording their highest sea temperatures on record in 2026. By the beginning of October, the Mediterranean remained significantly warmer than normal in parts of the region.

AEMET warned ahead of the storm that the combination of very warm Mediterranean waters and atmospheric instability could produce exceptionally heavy rainfall. In some areas of eastern Spain and the Balearics, the agency said rainfall could exceed 150 litres per square metre in six hours.

Heavy Rain Hits Ibiza

Ibiza and Formentera were among the areas affected when the storm reached the Pitiusas at the beginning of October.

According to AEMET figures reported after the episode, Ibiza received 49 litres per square metre and Formentera 18 litres per square metre over Friday and Saturday.

Together, those amounts represented roughly half of the rainfall normally recorded during an entire October in the Pitiusas.

The heaviest hourly rainfall recorded in Ibiza during the episode was in Sant Antoni de Portmany, where 38.9 litres per square metre fell in just one hour.

Sant Joan de Labritja also recorded a substantial 36.2 litres per square metre in an hour.

Storms Bring Flooding and Power Cuts

The intense rainfall was accompanied by considerable electrical activity, with thunderstorms lighting up the night sky across parts of the island.

Sant Antoni and Sant Josep were among the municipalities most affected. Flooding was reported in several locations, while firefighters were called to remove fallen trees in areas including Cala d'Hort and Cala Vedella.

Around 700 customers were also temporarily left without electricity because of faults affecting several areas, including Benimussa, Espartar and Es Canar. Authorities reported no serious injuries or major incidents from the storm.

Why Does a Warm Mediterranean Matter?

A warm sea does not automatically cause torrential rain, but it can provide additional heat and moisture to an unstable atmosphere.

That was an important part of the meteorological setup behind this particular episode.

AEMET explained before the storm that the Mediterranean was unusually warm for the time of year, with some areas more than 3°C above normal. At the same time, colder air was moving into the upper atmosphere, creating strong instability over the eastern part of Spain and the Balearics.

This combination can encourage the development of powerful thunderstorms capable of producing very intense rainfall over relatively short periods.

It is important, however, not to describe the warm sea as the sole cause of the storm. Atmospheric instability, moisture availability and the broader weather pattern all played a role.

2026 Has Already Seen Exceptional Sea Temperatures

The storm came after a summer during which sea temperatures around Spain reached exceptional levels.

Spain's state port authority, Puertos del Estado, reported in September that monitoring stations around both the Mediterranean and Atlantic coasts had recorded their highest temperatures since records began at several locations. Researchers have linked the broader rise in sea temperatures primarily to human-caused climate change.

The exceptionally warm waters also meant that the Mediterranean remained warmer than normal as autumn began.

That does not mean every part of the Balearic Sea was at a record temperature, however. Conditions vary considerably by location, depth and time, so it is more accurate to describe the region as experiencing exceptionally warm marine conditions rather than claiming a single record temperature across the entire sea.

A Sharp Contrast With September

The early-October storm also followed an unusually hot and dry September in Ibiza and Formentera.

AEMET's September 2026 assessment classified the month as “extremely warm” in both islands. Ibiza recorded an average temperature of 24.6°C, 1.8°C above normal, while Formentera averaged 25.6°C, 2.2°C above normal.

Rainfall during September was very low. Ibiza recorded around 10 litres per square metre compared with a normal September total of 76 litres, while Formentera also recorded only around 10 litres compared with its normal 44 litres.

The change at the start of October was therefore dramatic, with dry and exceptionally warm conditions giving way to thunderstorms and intense rainfall within days.

Autumn Weather in the Balearics

Heavy rainfall is not unusual in the Balearic Islands during autumn. The Mediterranean remains relatively warm after summer, while atmospheric conditions become more changeable.

AEMET's long-term climate data for Ibiza Airport show October has an average temperature of 20.2°C, with an average daily maximum of 24°C and average minimum of 16.5°C. Average October rainfall is 58 millimetres.

What made the early-October episode notable was the combination of unusually warm marine conditions and a highly unstable atmospheric setup, producing intense rainfall over short periods.

For Ibiza, the storm was a reminder that the island's autumn weather can change rapidly, even after a very warm and predominantly dry September.