From the looks of the concept art and the information on the Six Flags site about the location I think it is this piece of land on Google Earth. The shape of the coastline and the building work that is already to the top left of the park looks right and it matches with the (not very precise) location on their website.
Google Earth Coastline and potential park location
Source: Google Earth
Location as shown on Six Flags Park website
Source: https://content.sixflags.com/haiyan/about-the-park/
Concept Art from Six Flags website showing coastline and road layout
Source: https://content.sixflags.com/haiyan/about-the-park/