In late May , an area of disturbed weather began to persist in the South China Sea . The JTWC began to monitor the storm cluster on May 29 . The following day , the JMA reclassified the system as a tropical depression ; initially the system remained highly disorganized due to the lack of deep convection . Persistent moderate wind shear and dry air prevented the cyclone from strengthening significantly in the storm 's early stages . These conditions abated as the depression tracked northeast , and at 0000 UTC on June 1 , the JMA upgraded the system to Tropical Storm Nangka . Throughout the course of the day , Nangka continued to strengthen as it accelerated northeast , and peaked in strength with a barometric pressure of 985 mbar ( hPa ; 29 @.@ 09 inHg ) and maximum sustained winds of 95 km / h ( 60 mph ) , making it a severe tropical storm .