Twister

Whirling winds of doom, twisters (called "waterspouts" in the manual, although this is not accurate since they can appear on land as well; also informally known as "storms," "tornados," and "cyclones") could occasionally be found ravaging the Britannian countryside in Ultima IV.

Description
Particularly dangerous because of their ability to strike either at land or at sea, twisters also proved frightening because they could not be dispersed through combative means. Although not naturally aggressive, they could do significant damage to a party caught unaware and pulled into their swirling midst. In rare cases, aggressive twisters have been seen in the dungeons of Britannia. These special-case storms are likely creations of magic rather than natural phenomena, as they can be attacked and dispersed as though they were normal opponents, and even destroyed with the use of a Kill spell.

Twisters appeared only in Ultima IV. Their cousins, dust devils, were seen on 19th century Mars in Martian Dreams, and were larger and even more deadly.

Trivia

 * Twisters in the Ultima 4: Online Flash Version obscure the player's vision and can be attacked, though they cannot be struck or killed once on the combat map. There are reportedly 20 different "storm monsters" that can hide behind twisters.