There is a metal box beneath the air-conditioner unit to the left of the opening you came from (as you face it). Climb on the box and vault onto the pipe.

Turn right and jump up to grab the sill above the air-condition. Traverse to the right past the semicircular railing.

Pull up and go to the other side.

Hang from the sill and traverse to the right past the second railing.

Again, go to the other side of the sill and hang from the edge. Traverse to the right around the two corners and pull up on the small ledge.

Jump up to grab the cable above and traverse across. (Notice where Lara is positioned. If you stand on a different spot, you will not be able to grab the cable.)

You could grab the cable from the spot in front of the window, but Lara would have just enough strength to make it across.

When you reach the other side, you gain the strength upgrade. Drop down and turn right.

Continue to the end of the ledge and jump the gap.