This is as close as I can come to an accurate translation:
Nimbifer ille deo michi [sic] invidit osirim imbre tulit mundi corpora mersa freto invidia dira minus patimur fusamque sub axe. Progeniem caveas troiugenamque trucem voce precor superas auras et lumina celo crimine deposito posse parare viam sol veluti iaculis itrum radiantibus undas si penetrat gelidas ignibus aret aquas.
It is totally cryptic. The first word, Nimbifer, storm-bearer, might be a metaphor of trouble or mishap. I have inserted sic after the fourth word, michi, to show that it is correctly cited (I saw and photographed the inscription—sorry about the photo, but the plaque had a magical and potent bit of scaffolding in front of it), but I am not aware of a Latin word, michi. In context, it should be mihi (dative case of ego; i.e., to, with, of me). (It might be non-standard Latin or a mistake, but it's engraved in stone, a poor place for a typo! If it's a mistake, it might argue for a very late inscription when no one knew real Latin anymore. Or it might be a very recent restoration by cousin Pasquale, your friendly Neapolitan stone mason and classical scholar.) Who knows?
That bearer of storms was envious of my sun, sacred to Osiris, and with the rains washed away the bodies buried in the waters of the sea. Now we suffer fewer fierce calamities. Beware the evil progeny of Troy found beneath the heavens. I beseech with my voice the light of the higher spirits that when sin has been banished they may clear our way to heaven as does the sun sending forth its rays anew to penetrate and melt the frozen waters with warmth.