It's not nearly as hard as it might seem. Just look at the word, consider the spelling, and know that a lot of combinations of letters have colloquial sounds to them, For example, "au" together isn't always "ah-ooh", but is often pronounced as "ow," like you stubbed your toe. So "Hanauma Bay" sounds like "Hah-now-mah." (Although colloquial pronunciation drops the U sound, and it's spoken as "Hah-nom-ma." Even common words like Honolulu should be pronounced as "Hoh-noh-loo-loo," and not "Hah-nah-lu-lu."
Multiple vowels together are usually all pronounced. So "Kaaawa" (a community on the Windward side of Oahu) is pronounced "Kah-ah-ah-Va." Before you know it, you'll be ripping through some real tongue twisters, like Ke'eaumoku Street, Kalanianaole Highway, Piikoi, Ko'Olina, and Kapolei.
Now you're an expert.
Dave