Megastorm

Megastorm may refer to:

Hypothetical storms
ARkStorm, a proposed 1-in-1,000 year atmospheric river event that could impact California with historic, extremely damaging flooding
Hypercane - hypothetical extreme tropical cyclones that could reach the size of continents and last for several weeks on average. Hypercanes also would have maximum sustained winds reaching at least , and a minimum central pressure of  or lower.

Fiction
Megastorm, a Predacon/Destron in the Transformers Universe.