The cold air basically cleared the clouds over the south today, and the weather was clear and the air humidity dropped significantly. The temperature difference between day and night in the south has also begun to be on par with the north, and the minimum temperature in the hills south of the Yangtze River and East China is generally only 10-15 degrees in the morning, but the temperature can reach about 30 degrees in the afternoon. Under the clear sky, many places in the south ushered in a feeling of "autumn high and refreshing", as if this was not May but September.
1. The South China Sea water vapor counterattacked violently
As the dry air mass has the upper hand in the central and eastern parts of the mainland, the water vapor in Fujian, Taiwan, Guangdong, Jiangxi, Hunan, Hubei, and even Chongqing and Sichuan has been driven down to the sea or to the southwest.
However, this situation is about to change - after many places in the southern part of the mainland ushered in a rare good weather in autumn, a widespread precipitation process is also brewing. The latest forecast of the Central Meteorological Observatory points out that it is expected that before the 17th, the precipitation in the south will be small and weak; After that, precipitation will intensify in the south. From the 18th to the 20th, there will be a moderate to heavy rain process, with heavy rain in some areas, and locally heavy rain in southern Jiangnan and southern China.
This means that the south will face large-scale heavy rains or even heavy rains in the future, which will adversely affect transportation, agriculture and life in some areas. Behind this precipitation process is the violent counterattack of water vapor in the South China Sea and the rehearsal of the South China Sea summer monsoon.
What is the South China Sea Summer Monsoon? To put it simply, it is the southerly wind that prevails over the South China Sea from May to September every year, which is an important part of the Asian monsoon system and the main source of water vapor during the rainy season in the southern part of the continent. The strength of the summer monsoon in the South China Sea directly affects the precipitation and distribution in the southern part of the continent. After the outbreak of the summer monsoon in the South China Sea, the precipitation in the south will enter its peak stage. According to the supercomputer forecast, around May 18, with the change of the subtropical high pattern, a large number of southerly winds will drive a large amount of water vapor from the South China Sea into the southern part of the continent, and the once weakened heavy rain in the southern part of the mainland will strengthen again.
Second, a larger-scale rainstorm is brewing in the south!
Since it is already mid-May, not only is the land heating up further, but the ocean heat is also rising further, so that the ocean is forming a larger scale of water vapor. Therefore, from May 18, the heavy rain brought by the water vapor counterattack in the South China Sea may also be more violent.
At present, the forecast of the Central Meteorological Observatory points out that from the 18th to the 20th, there will be a moderate to heavy rain process in Jianghan, Jiangnan, South China, Sichuan Basin, Guizhou, Yunnan and other places, with heavy rain in some areas, and heavy rain in the south of Jiangnan and South China; Strong weather such as localized short-term thunderstorms and strong winds will occur in the above-mentioned areas. For example, in the rain forecast for May 20, there will be widespread heavy rain in the south, and at least five provinces will be hit by heavy rain.
For the mainland, the explosive strengthening of the warm and humid airflow may be a rehearsal for the outbreak of the summer monsoon in the South China Sea. After the outbreak of the summer monsoon in the South China Sea, South China will enter the dragon boat water stage with more violent rainstorms, and it will also further open the flood season on the mainland. The strength of the summer monsoon in the South China Sea will directly affect the amount and distribution of precipitation in the southern part of the mainland, and will also put forward higher requirements for the mainland's flood prevention and disaster reduction work.
Compared with the previous rainstorms, the rainstorms on the eve of the outbreak of the summer monsoon in the South China Sea will show the characteristics of warm-zone rainstorms that are more random and more difficult to predict accurately, and because the summer monsoon has been in a critical state of eruption, the water vapor transport is more intense, the warmth and humidity are more sufficient, and the intensity of local rainstorms may be greater. And how big this rainstorm will be, there is another variable, that is, those tropical clouds in the northern Indian and Pacific Oceans, which may intensify into cyclonic storm embryos, typhoon embryos, and even cyclonic storms and typhoons in mid-to-late May.