Water proofing west side facing wall

I've a top floor (4th) flat with west facing windows, during stormy rain the west side wall bleeds from inside along with the windows. I've decided to replace the windows with uPVC as this is a 10yr old construction and the builder had not been fair with the windows at that time. I would appreciate ideas how I can stop the bleeding walls would be highly appreciable. I'm located in Kolkata, so any water proofing experts can get in touch with me too. Just as a note, the walls only bleeds during stormy weather, I.e. when their is a stron west side wind, normal rains are fine.

Thanks.