Rainy weather can keep fruit from setting because:

1) Storms and rain tend to keep pollinators like bees away.

2) Even if you try to hand pollinate.. too much wetness can make the pollen too wet to stick to what it needs to stick to. Such as the brush or finger used to transfer pollen, or to the pistils intended to receive pollen.

3) a lot of water can wash nutrients out of the soil, causing the plant to not have adequate nutrients to set fruit. This can cause the plant to not resume production even after dry weather returns, unless more fertilizers are given to the plant.

I grow in containers, so when it gets *really* wet I move a few of my fave potted tom's under my porch roof to keep em dry, and hand pollinate them.

Hope this helps!