The update for 1.13 is being worked on, but there is no release date for it yet.
Updates to a new version of Minecraft take a lot of work, so please be patient.
Please refrain from making "is it done yet?" threads. The update will be ready when it is ready.
In the meantime, DO NOT fall for sites offering Forge for 1.13, these sites will NOT magically provide you with software that has not been released yet, they will more likely install malware on your computer.