Writing Feedback / The colours and sounds of Rain - imaginative writing [2]

I got a 600-900 essay assignment. Here is the topic:

Writing a piece called rain in which the narrator describes in detail his or her experience of unusual weather. In your writing focus on colours and sounds to help your reader imagine the scene.

now i can't think of what to write here, and how to describe and all. Im doing A level so i cant just write a silly childish essay either so im kind of stuck...any help? Maybe a first paragraph or a few points i can build on?

Thanks!