"It is raining."
I don't think so. "Pluvas", as the current tense of the verb "to rain", means "(It) is raining".
So "Ĝi estas pluvas" would literally be "It is is raining."
The "Ĝi" is implied, however I think you would still be OK with stating it explicitly, i.e, "Ĝi pluvas."
I'm far from an expert, so someone please correct me if I'm wrong. "Ĝi estas pluvas" was my response as well, but after it was marked as incorrect, I realized my mistake.
Make sense? Or am I missing something?
This may be an old question (cannot see it in the mobile app) but I would like to point out that in 40 years I have never heard "gxi pluvas" and do not consider it correct. There is no "gxi" that's raining. "Pluvas" Is impersonal, no subject.
For a longer expression you might say "pluvo falas" (rain is falling).