Direction of apostrophe in Hawai'i

My students are writing a case study about Hawai'i and we'd like to use the diacritical mark, correctly. My searches so far are turning up both

Hawai’i and Hawai‘i

Can anyone tell me a preferred form - should the apostrophe be "closing" as in the first form, or "open" as in the second form? Thank you!

It isn't an apostrophe: it is a distinct mark (letter, in Hawaiian) called ʻokina. In Unicode it is U+02BB ʻ MODIFIER LETTER TURNED COMMA

It resembles a left (or opening) quotation mark - your second option. This Wikipedia article discusses the different ways it has been represented where the system or font lacks it.