There's nothing unusual about getting hail when the ambient temperature is still above 20 degrees Celsius (68 F). Where I used to live, severe thunderstorms would often result in large hail. The temperature before the thunderstorm struck would very often be in the low 30s (Celsius). The most important process in hail formation is having a deep layer of cloud which is below zero degrees Celsius, and very strong updrafts. The strong updrafts are usually the result of strong surface heating, leading to "parcels" of air which are warmer and lighter than their surroundings. The stronger the updrafts you have, the longer ice particles will be suspended, and the larger the hail that forms. Melting occurs as the hail falls back down to the surface, but if the hail is large enough to begin with, you still get hail on the ground, even if the temperature is still quite warm. Naturally the temperature begins to rapidly cool with the onset of hail and precipitation (and the formation of a thing called a "cold pool", but that's getting into a lot of meteorological jargon which I won't expand upon here).