"Wow, Kona is humid!"
Translation:Hū ka ikiiki o Kona!
Just as a point of information, "hū" (or "hō" as another variation) are conversational words that are not generally found in Hawaiian dictionaries with this meaning. The closest word in more traditional Hawaiian is probably "kai," as in "Kai ke kolohe o kēlā keiki!" (Oh, how mischievous that kid is!) However, this is not so common in casual conversation today, so you'll probably hear either "hū" or "hō" instead.
For ' and for p, ka is standard, but ke is sometimes used. I think I've also seen ke used once with an h, so there may be other exceptions. But in general I believe you're right that it should be ke in front of k, e, a, and o and ka in front of other letters. And certainly in this sentence, before an i, ka is correct.
Because o connects two nouns and since ikiiki is being used as a noun, but it is not a proper noun, it needs a determiner. I'm just a student myself, but I think it is also fine to translate this English exclamation with a full Hawaiian sentence : Hū, ikiiki ‘o Kona. In this case, ikiiki is acting as a verb, and not a noun, so the determiner would be inappropriate, but the ‘o is on Kona because when using a proper noun as the subject of a verb, you have to mark it with ‘o.
Note, also, that it should be ka ikiiki, not ke ikiiki.
The o without the 'okina can be interpreted like English "of" - "the humidity of Kona". The 'o with the 'okina must be used to mark a propper noun used as the subject of a verb. Here Kona is not the subject of a verb, it is narrowing down which "ikiiki" we are talking about. So the o without the 'okina should be used.
I’m sure it is not. Ikiiki means both humid and humidity. So if you want to use it as an adjective you need to say ikiiki ‘o Kona. As a noun Ka ikiiki o Kona. Sometimes the correction seems to be wrong. To test any version you’d think might be right, try both (repeat test) and sometimes the correction shows other correct answers. That’s how I learned about several versions
I just commented, "Why is 'Hū ka ikiiki o Kona' ok for 'Wow, Kona is humid,' but for another exercise in this very lesson 'Ka ikiiki o Hilo' is NOT ok for 'Hilo is humid'?," and then came back again to the Hilo exercise (where, it turns out, I had asked the same question four months ago, as did Robin156446).
jdmcowan replied there, "I think you are both thinking of the exclamation that they gave before - Hū ka ikiiki o Hilo! That is more like "Wow the humidity of Hilo!" To say simply Hilo is humid, it would be Ikiiki ‘o Hilo.
(I decided that was worth a lingot and I'll try to remember it next time!)