Shortly before Friday’s tornado came ashore in Lanikai, Windward Oahu residents were hit with a hailstorm that dropped hail the size of baseballs.

The combination of tornadoes and large hail isn’t unusual because they often occur together in the same supercell thunderstorm, said Steven Businger, a professor in the Department of Meteorology at the University of Hawaii.

Tornadoes and hail are formed in an unstable atmosphere with strong updrafts, which are created by cold air high in the atmosphere while warm, moist Kona winds blow underneath.

When those updrafts combine with wind shear — changing wind speeds and directions with height — it leads to conditions for waterspouts or weak tornadoes over water.

Businger said waterspouts often form over the open ocean but go unnoticed by the public because they do not cause any damage. The recent vigorous storm, however, was "perfectly positioned" to produce a waterspout that made landfall on Oahu.

"The analogy would be there’s lots of tornadoes in Oklahoma, but few of them strike Oklahoma City," Businger said.