How to keep Lemon Meringue Pie from weeping
There are several tricks to insure this doesn't happen.
Heating the lemon juice with the sugar until it dissolves before adding it to the yolks will work every time. Sugar is hygroscopic so the undissolved granules will absorb moisture inside the pie and basically sugar syrup will leak out
Don't fill the pie crust with the filling until after the meringue is done. Keeping the filling in the pan (off the heat) keep it warm, and when the meringue is placed on hot filling, it helps to cook the meringue from the bottom so it doesn't over-brown in the oven. Brown at 350, no hiher. Usually I'm multi-tasking, cooking the filling, and whipping the meringue at the same time.
Also, if you place the pie in the refrigerator, that can start the weeping. If the pie is thoroughly sealed around the edges, with the meringue completely covering the filling and attached to the crust, it's fine to leave it at room temperature.