Ibiza's emergency authorities have explained why a regional ES-Alert was sent to residents on September 17 even though the most intense part of the forecast storm ultimately remained offshore.

Pablo Gárriz, director general of Emergencies and Interior for the Balearic Government, said the decision was based on the information available at the time, with forecasts showing the possibility of a powerful storm reaching Ibiza and Formentera during a critical period of the afternoon.

His central message is simple: on an island, a small change in the position of a storm can produce a very different result.

The alert was sent at 13:24

Residents of Ibiza and Formentera received the ES-Alert at 13:24 on Thursday, September 17.

The message called for maximum caution because of the forecast for intense rainfall and strong wind gusts and advised people to avoid unnecessary travel and outdoor activities.

People were also told to stay away from torrents and flood-prone, low-lying or underground areas.

At the time, the storm system was still approaching Ibiza and Formentera from the sea.

More than 50 forecast models were assessed

Gárriz said the Meteobal Technical Advisory Committee spent the hours before the alert analysing more than 50 weather-model scenarios alongside information from AEMET forecasters.

The committee was assessing several variables, including the probability of the event occurring, its potential intensity and the geographical area likely to be affected.

The decision was therefore not based on a single forecast.

Instead, emergency officials were working with a range of possible scenarios and their associated uncertainty.

Ten kilometres can change the outcome

For Gárriz, the key difficulty in forecasting emergencies in the Balearics is the islands' geography.

He explained that a deviation of only around 10 kilometres can make the difference between a powerful storm cell hitting an island and the same system passing over the sea.

That difference can dramatically change the consequences for people on the ground.

The storm that approached Ibiza on September 17 provides a practical example of that uncertainty.

The strongest part remained offshore

The most intense part of the system did not hit Ibiza and Formentera with the force that had been feared.

Instead, much of the strongest activity remained over the sea close to Ibiza's coast.

Gárriz said approximately 1,700 lightning strikes per hour were recorded near the coast and that more than 100 litres per square metre fell in an hour over the sea.

The fact that the most intense rainfall remained offshore meant that the Pitiusas experienced a less severe impact than the forecasts had warned was possible.

This does not mean the warning was based on an event that had no potential to affect the islands.

At the time the alert was issued, the storm was still approaching land.

Schools were warned before the public alert

Emergency officials also acted before the ES-Alert was sent.

Around an hour earlier, the authorities had contacted educational centres, management teams and families to facilitate the possibility of collecting children earlier than usual.

The intention was to reduce the number of people exposed to the storm during the period when the forecast conditions could have become most dangerous.

Gárriz said the educational community was considered one of the groups that could be particularly exposed because large numbers of children would otherwise be travelling at a similar time.

The afternoon classes were subsequently suspended, while centres remained available for students whose families could not collect them immediately.

Why send a warning that might not be needed?

One of the central questions surrounding the September 17 alert has been whether authorities should issue a warning when a forecast event may ultimately move away from the islands.

Gárriz acknowledges that using ES-Alert carries a cost when the expected impact does not materialise.

The system is designed for extraordinary situations and can immediately interrupt normal activity for people in the affected area.

But he argues that the alternative can be more serious when a dangerous storm does arrive.

His position is that emergency authorities must make decisions using the information available before the event, rather than judging the decision only after the storm's final path is known.

The alert followed an orange weather warning

At the time, Ibiza and Formentera were under an orange Meteobal alert for rain and thunderstorms.

The Balearic Government continued to monitor the situation throughout the day in coordination with AEMET.

Its official account later reported that the most intense rainfall in Ibiza had been concentrated in Vila, Sant Josep de sa Talaia and Sant Antoni de Portmany, with up to 40 litres per square metre recorded in one hour in those areas.

The Government said the forecast had broadly materialised, although the most intense rainfall did not fall directly over the islands.

Traffic problems followed the warning

The emergency measures had a noticeable effect on Ibiza Town.

The combination of the school-collection recommendation and the public weather warning led to a sharp increase in traffic on the city's main roads.

Many people were travelling at the same time, including parents collecting children, residents changing their plans because of the weather and visitors moving into central areas.

The resulting congestion lasted for several hours.

Emergency planning is about probability

Gárriz says weather emergencies cannot be managed with absolute certainty.

Forecasts provide an estimated probability, expected intensity and likely geographical area, but each comes with a margin of error.

For emergency authorities, the challenge is deciding when that probability is high enough to justify action that can affect thousands of people.

On September 17, the decision was to act before the storm reached the islands.

A different picture from the one forecast

By the end of the most critical period, Ibiza and Formentera had avoided the full force of the system that had prompted the warning.

That does not change what emergency officials were seeing earlier in the day.

The storm remained active close to Ibiza, electrical activity was significant and the potential rainfall was high.

The difference was where the most intense part of the system ultimately travelled.

The role of ES-Alert

ES-Alert is designed to send immediate public-safety messages to mobile phones located within a defined geographical area.

The technology uses mobile-network cell broadcasting, meaning authorities can target an area without needing a database of individual telephone numbers.

It is intended for emergencies in which rapid communication with people in a potentially affected area is necessary.

For Ibiza and Formentera, the September 17 message was used to reinforce the other warnings and instructions already being communicated by emergency services.

Lessons from recent extreme weather

Gárriz says recent severe weather episodes, including the major storms that affected Ibiza in 2025, have changed how risk is perceived in the islands.

The objective is to anticipate potentially dangerous situations rather than wait until the consequences are already visible.

That requires emergency plans, technical forecasting, coordination between agencies and, ultimately, decisions made under uncertainty.

Individual responsibility remains important

Gárriz also stresses that an emergency system cannot remove individual responsibility.

Authorities can issue warnings, activate plans and provide information, but people still have to decide how they respond to those warnings.

That includes avoiding unnecessary travel, staying away from flood-prone areas and following official instructions when an alert is issued.

What September 17 demonstrated

The September 17 episode provided a real-world example of the difficulty of emergency forecasting in the Balearics.

The storm did not strike Ibiza with the worst intensity initially feared, but the potential impact was sufficiently serious for authorities to take precautionary measures.

The experience also highlighted the challenge of communicating risk when the final outcome is uncertain.

For Gárriz, the lesson is that a difference of only a few kilometres can fundamentally change what happens on the ground.

In Ibiza, where land and sea are separated by relatively short distances, that margin can be the difference between a major weather event hitting populated areas or passing just offshore.