on may 19, the jtwc reported that an area of low pressure had persisted about 510 km (320 mi) to the southeast of yap. as the system moved towards the northwest under the influence of a subtropical ridge of high pressure, it rapidly consolidated in an area of light to moderate vertical windshear. the jma then started to monitor the system as a tropical depression later that day, before the jtwc designated it as tropical depression 04w early on may 20. the jtwc then reported later that day that the depression had intensified into a tropical storm with windspeeds of 65 km/h (40 mph), however it later reported that it had overestimated the windspeeds and consequently lowered the storm's status to a tropical depression, based on observations from yap island. late on may 21, both the jma and the jtwc reported that the depression had now become a tropical storm with the jma naming it as songda. over the next couple of days, the system gradually intensified further while moving northwest into pagasa's area of responsibility. pagasa named it as chedeng. at 1200  utc on may 24, the jtwc reported that songda had intensified into a typhoon. 12 hours later the jma followed suit while the system was about 800 km (500 mi) to the southeast of manila in the philippines. it rapidly intensified into a category 5 typhoon. in the afternoon of may 29, songda became extratropical south of shikoku island.