Following the completion of a flight in the local training area the aircraft was landed on Runway 36 at Roma. At the time the wind was north-westerly at five to eight knots and there was a thunderstorm to the south-west of the field. During the landing roll the wind velocity suddenly increased to about 25 knots. The aircraft swung to the left and ran off the side of the runway. The pilot was unable to regain directional control but shut down the engine before the aircraft ran into a ditch. This accident was not the subject of an on-site investigation.