The Turks are defeated by a storm before the battle even begins. It's one of the great Deus ex Machina (ghost out of the machine: an unexpected plot device that saves characters from a hopeless situation) moments in all of literature. The seeming threat of the Turks, so menacing to the Venitians in Act I, is over and done with before Act II even begins:
Othello is victorious. However, a greater threat looms on Cyprus: Iago and Roderigo plan to destroy Othello and Desdemona's marriage.
The storm is a pathetic fallacy, as it foreshadows the storm that is to come, the storm of jealousy that stirs in Othello.
The storm is also a red herring, as it is misleading threat that never materializes. Could Othello be the Turk that all of Venice feared in Act I?