The pilot was conducting a routine food and medical supply flight to several outstation settlements. Visual meteorological condition (VMC) existed when he departed, but with storm activity observed along the route, and a cyclone in the area. Approximately 1.5 minutes from the destination a rapid deterioration in the weather conditions to below VMC prevented the pilot from landing so he decided to divert to Oenpelli. He was again confronted by deteriorating weather conditions making further diversions necessary. He notified Adelaide Flight Service of the diversions and then attempted to return to his departure aerodrome, which also proved impossible. After spending sometime dodging around storms and heavy rain in an attempt to find a suitable airstrip, then faced with the approach of evening and fading daylight, he decided his safest action would be to find a suitable area for a precautionary landing. He was unable to re-establish contact with Adelaide Flight Service to advise his intentions. He found a relatively flat area on top of an escarpment, but during the landing roll the aircraft struck light timber causing the right wing to detach and the aircraft to roll onto its right side. The pilot and passenger evacuated the aircraft, then activated the ELT which was monitored by Airservices Australia SAR via satelite, and their location known. Because of the cyclone and adverse weather conditions a search could not be initiated until the next morning. They spent the night in the aircraft to shelter from continuous heavy rain, then rescued next morning by helicopter.