I definitely like the idea, but I worry that it might be too strong. The penalty to fire creatures, for instance; I don't think very many creatures even have more than 3 toughness. There's crimson dragon, fire spectre, and ash that I can think of off the top of my head. The pump for water creatures is probably balanced, though, seeing as there's no issue with nightfall/eclipse being OP/UP.
Perhaps the card should have a stated duration, the way wings or dimensional shield do, for example. It would make thematic sense; rain doesn't last forever, and it would make the card still strong against fire without being ridiculous. As printed it's an improved Eclipse for water, plus the bonus side effect of raping fire creature decks. Another solution could be to make the penalty to fire creatures only work on fire creatures when this comes into play, and have no effect on further fire creatures, but keep the water creature bonus permanently. It might also be a good idea to increase the cost of at least the upped version; right now the upped one costs the same as Eclipse, but it's better. The unupped one is better than nightfall, but also costs 1 more quanta, so that's reasonable.
edit: nymphs (both) and animated fahrenheit also have >2 hp