Legislating weather is a show of weakness before the Gods.
Caligula, now, he knew how to impress the Gods, more specifically Neptune. Several authors tell the story; here is Cassius Dio:
And when [Caligula] reached the ocean, as if he were going to conduct a campaign in Britain, and had drawn up all the soldiers on the beach, he embarked on a trireme, and then, after putting out a little from the land, sailed back again. Next he took his seat on a lofty platform and gave the soldiers the signal as if for battle, bidding the trumpeters urge them on; then of a sudden he ordered them to gather up the shells. Having secured these spoils (for he needed booty, of course, for his triumphal procession), he became greatly elated, as if he had enslaved the very ocean; and he gave his soldiers many presents. The shells he took back to Rome for the purpose of exhibiting the booty to the people there as well.
