Recently, the rain in the south has finally weakened. Since late April, Jiangnan, South China and other places have experienced multiple rounds of heavy rainfall and strong convective weather processes, resulting in floods, landslides, hail, thunderstorms and strong winds in some areas. For example, monitoring data shows that the average precipitation in Guangdong, Jiangxi, and Tibet hit a new high in April, and Longmen, Guangdong, set a record for the highest monthly precipitation at a national meteorological station in the mainland in April.
1. Heavy rains in the south are determined to intensify
On May 8, it can be seen from the satellite cloud map that the heavy rain in the southern part of the mainland is still in the weakening period, and the clouds in the southern part of the mainland are concentrated in the southwest and western parts of southern China.
According to the forecast of the Central Meteorological Observatory, the precipitation in the southern region will begin to strengthen in the coming week - according to the medium-term weather forecast of the Central Meteorological Observatory, on May 8-9, the heavy precipitation in Guangdong, Guangxi, the southern part of the Sichuan Basin, Guizhou and other places will be more scattered and the intensity will weaken slightly. From the 10th to the 12th, the precipitation in the southern part of the Yangtze River, the northern and western parts of South China and Guizhou will intensify again, and there will be two significant precipitation processes in the southern region around the 14th-15th and 17th.
2. The blue-purple rainy area spans 9 provinces!
The Central Meteorological Observatory predicts that in mid-May, the southern region will once again enter a rainy period, of which from the 10th to the 12th, there will be heavy rainfall in some areas of Guizhou, Hunan, Jiangxi, Fujian and other places.
According to the forecast, the southern region will enter a rainy period again in mid-May. It is expected that in mid-May, there will be more rainfall in the south, mainly around May 10-12, 14-15, and 17. From the 10th to the 12th, there were heavy to heavy rains from west to east and from north to south in central and eastern Guizhou, Jiangnan, and central and northern parts of South China, and heavy rain in parts of central and southern Hunan, central and southern Jiangxi, and western Fujian. As can be seen on the forecast map, the blue-purple rainy areas span Sichuan, Chongqing, Guizhou, Guangxi, Guangdong, Hunan, Jiangxi, Fujian, Zhejiang and other provinces.
So, how did this constant southern rainstorm come about? In general, the formation of heavy rainfall requires two conditions: one is sufficient water vapor and the other is a strong uplift mechanism. Water vapour is the material basis of precipitation, and without water vapour, there is no precipitation. The uplift mechanism refers to the force that causes the air to rise, and the rising air will continue to cool and form clouds and precipitation when it reaches saturation. Common lifting mechanisms include topographic uplift, thermal uplift, frontal uplift, etc.
Several important meteorological systems play a key role in the formation of heavy rainstorms in the south – the warm and humid airflow, which is the main source of water vapor for the south, is the warm and moist air flow blowing from the oceans at low latitudes. Warm and humid airflows are usually controlled by the subtropical high and change with the change of the subtropical high.
The activity of the warm and humid airflow is related to the southern branch trough and the subtropical high, which refers to a large ridge of high pressure in the western Pacific Ocean, which is the main controlling factor of the climate in the southern part of the continent and affects the precipitation and temperature in the south. The southern branch trough is a trough of low pressure south of the Tibetan Plateau, which is an important weather system affecting precipitation in southern China, especially in winter.
During the heavy rain in the south, the subtropical high was stronger, so that the warm and humid air flow from the South China Sea and the Bay of Bengal was continuously transported to the southern region, providing sufficient water vapor for precipitation. At the same time, the eastward movement of the southern branch trough provides an opportunity for the warm and humid airflow to rise, resulting in the development of convective clouds, forming a falling area of heavy precipitation and strong convection. On the other hand, the cold air from the north is also moving southward, forming a front with the warm and moist airflow, increasing the intensity and extent of precipitation. As a result, there has been a continuous heavy rainfall and severe convective weather process in the southern region.
In conclusion, the formation of heavy rainfall in southern China is the result of the interaction of multiple meteorological systems, among which warm and humid airflow, subtropical high pressure, southern branch trough and cold air play an important role. In the coming week, the precipitation in the southern region will continue to strengthen, and heavy rain will occur in some areas, accompanied by severe weather such as thunderstorms and strong winds.