Taanis 3:6-7

Taanis 3:6

On one occasion, some elders went from Jerusalem to their own cities, where they decreed a fast because a hot wind, sufficient to destroy the contents of an oven, was witnessed near Ashkelon. They also decreed a fast because two children were devoured by wolves on the other side of the Jordan. Rabbi Yosi said the fast was declared not because the wolves actually devoured anyone, but just because they had been seen.

Taanis 3:7

For the following crises the shofar is blown even on Shabbos: a city threatened by enemies or a flood, and a ship being tossed at sea. Rabbi Yosi says that blowing shofar in such cases is to call for help, not to beseech God. Shimon HaTimni says we also blow shofar on Shabbos because of a plague but the Sages did not agree.