In Act 2 Scene 1, What major natural occurrence has changed the course of the play? What has happened to the Turkish Fleet?

Storms are always of greater significance in Shakespeare; here, the storm is a symbol of unrest, and of discord to come. The storm marks the end of the peaceful part of the play, and is an act of fate; though it is doubtful that the storm will be as significant in the plot as the storm at the beginning of The Tempest, it is a signal that Iago's mischief is about to begin. Shakespeare's characters that comment on the storm are mariners, alluding to Ursa Minor and stars used for navigation; this is a testament to Shakespeare's incredible ability to form credible language for a great diversity and range of characters. It would appear that the Turkish fleet have had their ships broken yp by the storm and are drowned,

If that the Turkish fleet

Be not ensheltered and embayed, they are drowned.

It is impossible they bear it out.