agreed with ckuang about using a telephoto lens which is useful in situations as such and also during the whole wedding event for zoom-in creativity and expressions shots.
It happened to me once before when it was downpouring so heavily that even with an umbrella, it is still going to get you and your gear wet. So i stood in the shelter (HDB void deck), took out the 2nd camera with a 70-200 attached to it and shoot the 'welcome the bridegroom' pics.
Since it is rainning, I am sure you will not have relatives running out to welcome the bridegroom except the poor chap who has been assigned. Therefore, it should not be too difficult to get a good angle.
Good luck and believe me, your experience grows as you shoot more and more.
Cheers and God bless,
Originally Posted by ckuang