because you have a terrible signal to AP and the handshake between client and AP could not be captured due the distance you have .
You need to keep airodump monitoring that AP and writing the data to a file , and in the process you should use aireplay to do a death authentication to the current client connected to that AP .
That will disconnect the current client and then it will make the client reconnect again to the AP and you got another chance to capture the handshake .
I dont know how much power you have in your wifi card , but if it is a card with at least 1W power then you should input a power increase using "iw reg set BO" in a terminal , and restart the wifi card so the wifi increase power get applied .
If your wifi card is a regular card with 200mw power then it will be extremely difficult for your death authentication arrive at the client .
read this manual :
http://www.aircrack-ng.org/doku.php?id=cracking_wpa
