Both a geometrical correction and a residual error correction schemes are proposed to improve the positioning accuracy of a three-frequency differential global positioning system (DGPS) on the order of centimeters, using 1 s of received data, and the baseline can be up to 120 km. An ad hoc network of floating dropsondes bearing DGPS receivers is proposed to monitor the progress of a typhoon in real time. An empirical typhoon model is adopted to simulate the deployment of such a network in typhoon Morakot and hurricane Katrina to verify its feasibility.