Good evening. This weekend marks the beginning of Fix and Fortify work on the Clark St tunnels. 2 and 3 trains will not run between Manhattan and Brooklyn. Expanded 4 and 5 local service will replace normal service from 7th Avenue. This service change will be in effect every weekend through April 2018.
Shifting gears, there are several other service changes to contend with. J and M trains are once again not running past Crescent St and Myrtle Av respectively. Shuttle buses replace G trains between Bedford-Nostrand Avs and Court Sq. As usual, there is no service along the Dyre Ave line.
Finally, there are a couple of major reroutes in place. E and F trains are running local in Queens in both directions. Speaking of the latter, F trains are running via the E and C lines from Roosevelt Av to Jay St.
Enjoy the weekend.
SUNDAY EDIT: As mentioned in the comments, N trains are running normally in Brooklyn. The map linked above has been updated to reflect this. Apologies for the late update, but I was away from my computer for all of yesterday.