The text warnings on met.no are discontinued but are available on Værio.no.

Go to værio.no to create a user account.  
You can also go directly to the text warning on Værio (login required).  

On Værio, you can also set it up so that you receive text warnings via email (select the product "Text Warnings," click on the three vertical dots in the upper right corner, and select "AutoMail").  

Værio is a tailored weather service for public sector partners and users who require specialized weather services.  
The service's primary geographical area is Norway and the Norwegian Sea, as well as parts of the North Sea, the Arctic Ocean, and the Barents Sea.  

On Værio, you can get an overview of the weather with the data you want.  
You can create your own setup and save it so that you can use it as a standard tool (this is one of the reasons Værio requires login).  

Contact Værioif you encounter problems with logging in.