Sharing on how you can design your application. Don't treat your application as a one-to-one mapping to the website.
Your mobile application is like a collector to the HWZ site information. You can always consult multiple URLs of the forum to retrieve all the information that you need to present a view in your application.
Got example, suppose your application provides a feature that allows any user to nitpick on as many sub-forums as they wish and group them into a list called "My Favourite Forums". In this case, "My Favourite Forums" does not exist in HWZ. But you can follow a list of favourites configured by the end-user, to fetch from the corresponding URLs to fetch back multiple pages of HTML. Parse through these HTML pages for the posts in each of them, formulate your own data model in your mobile app and display them in the consolidated view.
In the realm of your own app, you design your concept of how information are consolidated and displayed. You don't need to follow the source unless that is your intention. You can do things like periodically access some pages to get updated information even if the user did not initiate it to provide features like intelligent preloading based on end-users' access patterns on frequency of visits, recentness of visits, and so forth. Then updated information can be force updated on the mobile app even if the user did not perform a reload. Whether this make sense or not, depends on what you want your application to be like.
You could also have "My Followed Threads" view, which will then consolidate threads from all over the forum and formulate into a single list within a view. Manipulating individual posts in this list, will be analogous to someone clicking on the browser into the forum, then into the specific thread, scroll to the post, reply, edit, or so forth. But you don't need to follow this workflow. All you have is REQUEST/RESPONSE, you can free to jump from one REQUEST to another which can be totally unrelated.
Hope you get a better idea for your endeavour.