Imagine Earth was hit hard by some force so devastating that Earth now has an axial tilt of 90.0 degrees, a far cry from the usual 23.5 degree. The same force somehow eliminates the Moon. In my story, Earth now obliquity oscillates between 89 to 91 degrees and will remain so for another 13000 baktun cycle of the Maya Long Count calendar. With the tides and seasons out of the way, I am wondering: could tornados still form? If so, what mechanism would drive such vortices?
More important factors include things like the overall energy of the storm and pressure dynamics.
Due to the proximity to the sun and the abundance of water, this skewampus version of earth will still have weather. This includes tornadoes. (It will likely not be the current weather patterns, though!)