Afaik ther eis no such addon already out here.
As this is definately something that you "need to check on official sites", or the launcher (it already shows this today, so why don't you read it there before login if you do not want to check the forums?) and then manually transfer it to an addon + keep it updated:
I doubt anyone would invest the time to create such an "addon".
Don't get me wrong but the forecast for re-occuring events, well, why would one need an addon for this at all?
Create a reminder in your smartphone
Or another idea - You can learn lua and code this addon yourself, maybe others are happy to get it as well. You'd see what effort it takes and needs to keep it updated, as there is no way to get the data by the help of ingame API or from external sources "automatically" (communication is blocked!).
Maybe it's your next hobby :-)
If you know other coding languages:
https://wiki.esoui.com/New_to_lua%3F_GOTCHA
https://discuss.codecademy.com/t/learning-lua/352032/2
If you do not know other coding languages:
https://www.tutorialspoint.com/lua/index.htm
Google e.g. search for "learn to code" and you'll find books, youtube videos, codecadamy and other free ressources
Eso uses LUA 5.1 with Havoc Script
https://wiki.esoui.com/Esolua
Addon structure:
https://wiki.esoui.com/Addon_Structure
Addon txt manifest:
https://wiki.esoui.com/Addon_manifest_(.txt)_format
Tutorials how to build your first addon:
https://wiki.esoui.com/Main_Page -> Right side -> Tutorials
Addon dev chat:
https://gitter.im/esoui/esoui
For the ESO feature please contact them at the official forums and ask for the feature. Meanwhile you see events ingame already as they occur (bottom left box at char selection or bottom whole screen box sometimes) meanwhile, so maybe they can add a kind of forecast info as well.