I bought a home with a screened in porch on the back. When it rains, I get about 2" of water on the concrete inside my screened in porch. It's running in from under the door that opens to my backyard. Do you have suggestions on what I can do to prevent water coming in? There's about a 1" opening under my door that opens to the backyard (grass)

Obviously your back yard slopes down toward the door so that rain water is delivered right there. There are two ways to solve the problem. Depending in the grades all around your house, you could regrade the yard to produce a swale about 6 feet out from the porch door, which should be graded to direct the water around the house. The alternative is to install a yard drain about 6 feet from the door, and slope the yard down from the door to the drain. Depending on the amount of water and the soil type in your yard, the yard drain could be piped to a drywell, or it could be piped to daylight somewhere still on your property, or to a municipal storm drain if available.