I think the way we were taught it on here, it would be "He lā mālie kēia", I don't know if the dummy pronoun can be implied in Hawaiʻian too, but let's wait for somebody who knows what they're talking about! xD
Technically yes. With weather, "it is..." sentences in Hawaiian do not need a subject. Ke ua nei. means It is raining with no subject. I think I put It is a calm day, and it was marked wrong. However, the first word is capitalized and there is a period at the end. It is misleading at the very least.
The (capital) at the beginning and the (period) at the end makes one want to type out a complete sentence for the answer. I wish they would remove (the period) to indicate an incomplete sentence / fragment.