Tropical Storm Rumbia was a rather weak but very destructive tropical cyclone that caused widespread and disastrous flooding in East China in August 2018. The twenty-second officially recognized tropical cyclone of the 2018 Pacific typhoon season, Rumbia developed from an area of low pressure that developed southeast of the Ryukyu Islands on August 13. Favorable environmental conditions supported development of the low into a tropical depression by August 15. At 12:00 UTC that day, the depression strengthened into Tropical Storm Rumbia, which refers to the Sago Palm. Initially moving northward, the cyclone turned westward in response to a building ridge to its northeast while slowly strengthening, reaching its peak intensity with maximum 10-minute sustained winds of 85 km/h (50 mph) on August 16. At 20:05 UTC that day, the storm made landfall in Shanghai at peak intensity, maintaining its strength as it moved inland due to ample environmental moisture. However, Rumbia began to weaken as it continued further inland, degenerating into a tropical depression on August 17 shortly before becoming extratropical over central China. The extratropical remnants of Rumbia accelerated northeastward into the Russian Far East, where they dissipated on August 23.
Rumbia, the third tropical cyclone to strike East China in 2018, succeeding tropical storms Ampil and Yagi, produced widespread heavy rainfall over regions already saturated by rains from the previous storms, causing flooding which claimed 53 lives and destroyed thousands of homes throughout the northeastern provinces of Anhui, Henan, Jiangsu, Shandong, and Xuzhou. Total economic losses from Tropical Storm Rumbia are estimated at ¥36.91 billion (US$5.36 billion).
Meteorological history
On August 13, 2018, the Joint Typhoon Warning Center (JTWC) began monitoring a weak area of low pressure to the south-southeast of the Ryukyu Islands. Disorganized convection accompanied the low, primarily south of the circulation due to strong westerly flow. Environmental conditions consisting of low wind shear, high sea surface temperatures (averaging ), and an anticyclone aloft favored development of the low. At 06:00 UTC the next day, the Japan Meteorological Agency (JMA) classified the system as a tropical depression. Steady development took place throughout the day with convection blossoming near the elongated circulation center. Curved rain bands signified increasing organization and the JTWC issued a Tropical Cyclone Formation Alert later on August 14. Around 12:00 UTC, Kadena Air Force Base in Okinawa—roughly north of the system's estimated center—recorded sustained winds of and a pressure of 998 hPa (mbar; 29.47 inHg). The JMA subsequently analyzed the system as a tropical storm at 03:00 UTC on August 15—the eighteenth tropical storm of the season. Accordingly, the storm was assigned the name Rumbia. At the same time, the JTWC designated Rumbia as Tropical Depression 21W.
Throughout August 15, Rumbia moved slowly northwest in response to a subtropical ridge to the northeast. Intensification was slow to occur as convection remained disorganized, primarily active to the south and east of the center. Accordingly, the strongest winds were displaced well east of the center within this convection. The outlying convection remained strong due to ample upper-level outflow. An upper-level trough suppressed convection over and west of the center, leaving the circulation exposed. Early on August 16 Rumbia's trajectory shifted west-northwest, bringing the expected track toward Shanghai, China. The upper-level environment became more conducive to development throughout August 16, with improved outflow supporting development of convection over Rumbia's center. A nascent eye feature surrounded by deep convection became evident later that day, marking intensification of the system. Based on JMA analysis, Rumbia reached its peak intensity around 15:00 UTC just east of Shanghai with winds of 85 km/h (50 mph) and a pressure of 985 hPa (mbar; 29.09 inHg).