The islands of Ibiza and Formentera were placed on red alert for torrential rain on Sunday.
Red alerts, the highest level of warning, are not particularly common in the Balearics. They are more common on the mainland; parts of Valencia are on red alert on Sunday and Monday.
Storm Adam could see up to 90 litres per square metre of rain in one hour, the alert having been raised from amber and applying to the period 11am to 2pm; the amber alert is in place up to 3pm Monday.
A Civil Protection alert was sent to all phones in Ibiza and Formentera at 11.20am, warning of an "imminent risk of flooding". Authorities were urging maximum caution, advising the public to "avoid flood-prone areas, refrain from unnecessary travel, and stay away from torrents".
There has already been significant flooding in Ibiza Town.