It was still raining. As soon as I stepped outside I met Uncle Caesar.

VOA: special.2010.06.12

"It's" with an apostrophe is short for "it is," as in "It's raining."

VOA: special.2010.02.11

One day it started raining, and it didn't quit for four months.

VOA: standard.other

It has not stopped raining and officials say this is hampering efforts.

VOA: standard.2009.10.03