New research conducted by University of Washington scientists Tsubasa Kohyama and John M. Wallace suggests the moons gravity may actually reduce the amount of rain in any given area, very slightly.
Think of it like the tides. The moon's gravity plays a huge role in our low and high tides along the coasts. According to Kohyama and Wallace's research, the moon's gravity can 'tug' on the atmosphere, making it bulge out toward the moon. The result is higher air pressure in the atmosphere, and high temperature at the surface. Since a warmer parcel of air can hold more water, less water will be condensed as rain.
The research lasted from 1998 until 2012, and used data from NASA and the Tropical Rainfall Measuring Mission. While the result suggests the moon's gravity is reducing rainfall, it's only by a very small margin; a change about 1% in total rainfall variation.
This means it won't affect agriculture or forecasts, but it will still be useful for future climate research.