"Wow, it's hot!"
Translation:Hū ka wela!
i thought the same, but perhaps aue has a different meaning that hu. Eg. I guess that hu is a negative "wow" of annoyment. If you say "aue ka wela" perhaps it means that you are happy that it is so hot, and perhaps it doesn't make sense.
Perhaps a tutor can confirm this, and it should be explained in the comments or the introduction notes.
I always believed that Auē was more Alas! Too bad! as opposed Wow + anything pleasant. About Aūe, my dictionary says: "Much used to express wonder, fear, scorn, pity, affection." Thatʻs pretty much where I am with the word. I looked up hū, too, since I was on a roll. It describes "to rise or swell such as yeast or souring poi" or emotions rising to the surface. "Hū ka ʻaka to burst into laughter." I mention these things because it seems as if Duo treats them in the same way, but I do feel that aūe and hū each have their own place among interjections.
@KiUlv and @DABurnside agreed. If people have not experienced using these exclamations first hand or heard them used first hand I would refer you to "Pidgin to Da Max" by Douglas Simonson, Ken Sakata and Pat Sasaki to get into the feel and phrasing of these kinds of expressions. There are different dimensions to the Hawaiian language, "Pidgin to Da Max" books will help with certain aspects of the language, how to think and feel in Hawaiian in some of these ways.