Core Viewpoint - A new round of heavy rainfall, the strongest of the year, is set to impact a large part of southern China starting tomorrow night, with significant risks of disasters due to extreme rainfall levels [1][6]. Group 1: Rainfall Intensity and Characteristics - The rainfall from the 27th to the 29th will see areas in Guizhou, Jiangnan, and southern China experiencing heavy to torrential rain, with some regions receiving 100 to 180 millimeters, and localized areas potentially reaching 250 to 300 millimeters [1][6]. - Short-duration heavy rainfall is expected, particularly in regions like Guizhou and southeastern Fujian, where localized rainfall could exceed 80 millimeters in a short time [3][10]. - The current rainfall system is characterized by a low vortex shear line moving eastward, combined with moisture from the Bay of Bengal and the South China Sea, leading to optimal conditions for heavy rainfall [6][10]. Group 2: Affected Areas and Coverage - The rainfall will cover a vast area, with heavy rain expected across multiple provinces including Guangxi, Guangdong, Hunan, Jiangxi, Fujian, and Zhejiang, marking the largest affected area this year [5][11]. - The rainfall intensity and coverage are anticipated to surpass previous rainfall events, with significant overlap in affected areas from earlier rainfall events [11][13]. Group 3: Disaster Risks and Historical Context - The overlapping of heavy rainfall zones increases the risk of mountain floods, geological disasters, and urban flooding, necessitating heightened vigilance and risk assessments in affected regions [11][13]. - Since May, southern China has experienced five rounds of significant rainfall, with some areas seeing precipitation levels 30% to 80% above normal for this time of year, and localized areas experiencing up to double the usual amounts [13].

Core Viewpoint - The southern regions of China are experiencing frequent heavy rainfall since May, with the most intense rainfall expected from May 27 to 29, posing significant disaster risks due to overlapping heavy rain areas [1][3][4] Summary by Sections Rainfall Patterns - Since May, southern China has seen three significant rainfall events, with areas like Guizhou, Guangxi, northern and western Guangdong, northern Jiangxi, southern Hunan, and southern Zhejiang experiencing rainfall amounts 1 to 2 times higher than the same period in previous years [1][3] Upcoming Rainfall Forecast - From May 27 to 29, the southern regions will face the strongest rainfall of the year, characterized by a wide range of rainfall, high intensity, and large daily rainfall amounts. Areas expected to see heavy to torrential rain include eastern and southern Guizhou, western and southern Hunan, southwestern Jiangxi, Fujian, northern Guangxi, and northern Guangdong, with some regions potentially experiencing extreme rainfall and severe convective weather [1][3] Seasonal Weather Influences - This round of heavy rainfall is likely associated with the onset of the South China Sea monsoon, which significantly alters wind patterns and precipitation in the region, marking a critical transition in the climate of East Asia and India. The onset of the South China Sea summer monsoon this year is expected to be slightly later than the average date of May 4 [3] Disaster Risks - The overlapping heavy rainfall areas increase the risk of disasters, particularly in regions such as western and southern Hunan, southern Jiangxi, southern Fujian, northern Guangxi, central and northern Guangdong, eastern and southern Guizhou, and western Yunnan. Potential secondary disasters include mountain floods, geological hazards, small river floods, urban flooding, and agricultural waterlogging [4]