what function does the severe storm at the opening of this scene have in terms of the plot of the play act two scene one

Storms are always of great significance in Shakespeare; here, the storm is a symbol of unrest and the discord to come. The storm marks the end of the peaceful part of the play, a signal that Iago's mischief is about to begin. The storm is also a great example of Shakespeare's deft use of language. The characters that comment on the storm are mariners, alluding to Ursa Minor and stars used for navigation; this is a testament to Shakespeare's ability to craft credible dialogue for a great diversity and range of characters.