I think an alternate translation of "How is the weather in Hilo today" should also be an option
o Hilo = of Hilo / Hilo's
i Hilo = in Hilo
I think they are trying to teach the difference between the two, and so it was not accepted as first. Just a guess, though.
How's the Hilo weather today? wasn't accepted, but I would think it should work as well.
"Pehea ke anilā o Hilo i kēia lā?"
"How is the weather of Hilo in this day?" =
How is Hiloʻs weather today?