The solomon Islands
In the book South Pacific is based off of, most of the action takes place in the Treasury Islands, which are the Western part of the Solomon Islands. The volcanic island, Bali Hai, is not real. The fictional island is likely named after a village Michener mentions in his book.
The Solomon Islands have an average temperature of 71 to 90 degrees Fahrenheit. They can be very humid. November, when South Pacific takes place, is the hot season for the islands.
Solomon Island Basics: