Police are investigating a possible stabbing in Waikiki Friday night. Paramedics were called to Monsarrat and Campbell avenues at 10 p.m. where they found a 27-year-old woman with injuries.  They transported her to a trauma center in serious condition.  Police closed  Campbell Avenue in both directions between Kaunaoa Street and Monsarrat Avenue while they investigated the incident. The road was reopened at about 12:30 a.m. Saturday.