It would be even nicer - although none of the ambient/white noise generators I've seen so far does that - if one could control the intensity of the rain or make it do that little thumping sound when rain drops hit the window.
Don't get me wrong, though - this is very nice! Especially as it's a cold-ish, rainy day outside where I live.
It dynamically generates the audio based on the samples you select and in advanced mode you can adjust the variance, frequency, looping, etc.
I made two huge mistakes based on bad assumptions (it was my first iOS app)
1: that you wouldn't want to edit the storm while it was playing. I have the code working now to do live updates and should be releasing it soon.
2: that people would care more about the audio than a fancy UI since you spend the vast majority of the time listening (not looking). Boy was I wrong! I still haven't gotten a good designer to help me tidy it up.
If you like it don't buy IAP in the free version - you can get the same stuff for $4 cheaper in the paid version.