Apparently there is no filtering on the intake air, so when it rains I guess the water droplets just get sucked in by the wind.
You should have three things on your intake side. A weather hood is needed to prevent the rain pouring down. You will also need what's called a metal pre-filter or mist catcher so that the velocity of the air doesnt pull in water. The mist catcher is also good for humid climates. And then of course your regular paper filter after the pre-filter.