Light rain...yes.
do you mean to park it in the rain? No, the material is to thin and not rain proofed at all. It will eventually soak through.
A bikini top is, to provide shade and relief from the sun while driving top down. And to keep the frontal part of the cabin warm'ish on cooler nights.
If you require a good "seal" and solid rain proofing buy the front part of a hard top. I think Rally tops is now selling just frontal parts.