Hail the size of golf balls and baseballs can only form within intense thunderstorms called supercells. These supercells need warm, moist air to rise into progressively colder, drier air, as well as winds changing direction and increasing speed with increasing height off the ground. For both sets of conditions to exist at the same time in Hawaii is extremely rare, but that did occur on 9 March. Conditions that day were ideal for a supercell to form — which on National Weather Service radar imagery looked very much like that from such storms in the central portions of the contiguous United States where severe hail larger than 2.5 in diameter is most common.
Supercells can also produce tornadoes, another rarity in Hawaii.