The html folder 'weewx' you refer to is created nominally as
/var/www/html/weewx (for package installs - for setup.py installs the directory
/home/weewx/public_html is used instead). In either case the directory is not actually created during the WeeWX installation process, rather it is created the first time WeeWX generates output during a report cycle. So if you have truly only installed, but not yet run WeeWX, then the directory will indeed not exist. I'm guessing though that you have started WeeWX or it was started during the package install process, in that case if the directory does not exist then that indicates either a report cycle has not yet been run that generates output. This is likely due an an error being encountered by WeeWX. Have you checked the log? If not that is you first port of call. If you cannot work out the problem from the log I suggest you post a log extract here. If you do not know how to obtain a suitable log extract I suggest your refer to and follow the instructions in the wiki post
Help! Posting to weewx-user.