How to install WRF on a Mac?
The WRF Forum here describes some testing using a Mac, and they report success with 2 setups:

Mac 64-bit running OSX, with Intel chips, g95 gcc version 4.0.3 (g95 0.92!)

Mac 64-bit running OSX, with Intel chips, PGI pgf90 10.3

There is also some additional information on installing ARWpost on a Mac found on the WRF Forum.

Separately, there is a blog dedicated to your question here and instructions on github here.  Also, if you see the tutorial here, you can see a method that requires you to install Xcode.