We observed four dry intrusions that occurred over Sumatera Island (Sumatra) during the intensive rawinsonde observation periods in 1998-2004. The events were accompanied by westerly winds, and included the passage of a single organized synoptic-scale cloud system, with a structure similar to a squall line. The cloud systems had the properties of a Kelvin wave. Eastward propagation speed was around 13 m/s, and the horizontal scale was several thousand kilometers. Severe rain occurred as the cloud systems passed, and dry intrusion suppressed convections in the rear part.