It seem I may have found out how to create multiple tornadoes. I tested this a few times and the number of tornadoes seems to rely on enemies near you, within your your range. I was doing defense missions, sniping far up above with no enemy near me. When I used my tornado power I would only conjure one.
When heavily surrounded standing by the defense pod, I created 5 tornadoes. The number seems to vary based on thw amount of enemies.