When it storms, the detection range of drowned is drastically increased. They will now spot you from almost any distance. Also is their spawn rate much higher, and they're much better equipped.
With these changes in place you'll have to fight an invasion of drowned during a lightning storm emerging from a nearby sea. Not only that, the the fight will be much more epic, since more drowned carry tridents with them, and most of them will be enchanted as well.
This will also be the best time to go out and get a trident, since more drowned with a higher percentage carrying tridents means more tridents being dropped as well.