With the arrival of July 2024, the central and eastern regions of the mainland are ushering in remarkable weather changes - this afternoon, you can see that the plum rain belt is gradually "erecting", with Dongting Lake as the center, the east rain belt has been lifted north to Hubei and Anhui, and the slender rain belt on the west side is approaching the north of Guangxi, which is a manifestation of the formation of a cyclone. Tomorrow, the main rain belt will run through the vast area from Guangxi to Jiangsu, Hunan is still the focus of heavy rain, and Guangxi and Hubei are also raining strongly.
1. Jiangsu, Zhejiang and Shanghai have been determined by continuous high temperatures this week
In the past June, the rainy season that continued to rely on the southern part of the mainland was a typical plum rain rarely seen in recent years, but this typical plum rain belt is also really powerful, for example, in Hunan, Changsha, the oldest national station, set a new record for the most monthly rainfall (640.3 mm), which was recorded during the famous 1998 Yangtze River basin flood.
According to the forecast of the Central Meteorological Observatory, starting from July 2, there will be continuous high temperature weather of 35 degrees and above in Hangzhou, Zhejiang. And this hot weather seems to have no end in sight this week.
The northward lifting of the subtropical high is undoubtedly one of the main reasons for this hot weather. According to the latest meteorological data, the central ridge of the subtropical high will be lifted from Taiwan, Fujian, and Guangdong all the way to the north to the first line of Zhejiang, Jiangxi, and Hunan. This process will be completed around July 3, and the lower reaches of the Yangtze River will usher in a period of hot weather, especially in the Yangtze River Delta region. Residents of this area will face continuous scorching heat.
2. Is the rainy season completely over this year?
When the high temperature hits, it is not only the high temperature numbers that are unsettling, but more importantly, the high temperature is accompanied by high humidity. According to supercomputer simulations, the humidity will also remain at a high level during the high temperature in many places in Jiangsu, Zhejiang and Shanghai, such as in downtown Shanghai, on the afternoon of July 4, the relative humidity will exceed 60% at the same time. This means that Jiangsu, Zhejiang and Shanghai will face a very uncomfortable damp heat and high temperature. This kind of hot and humid environment has a particularly obvious impact on the human body, which is easy to cause health problems such as heat stroke, and everyone needs to take more precautions.
In the rainy season every year, Jiangsu, Zhejiang and Shanghai are always inseparable from continuous rainfall. This year's rainy season seems to be no exception. However, in the process of the northward lifting of the subtropical high, the plum rain in the lower reaches of the Yangtze River seems to be coming to an end. According to the forecast of the Central Meteorological Observatory, heavy rainfall will continue in the middle and lower reaches of the Yangtze River from July 1 to 2, but from July 3, the rainfall will weaken significantly, and the rainfall will enter an intermittent period from the 4th to the 8th. Does this mean the end of the rainy season?
3. Be wary of Erduanmei
The answer may not be so simple. Although the high temperature brought by the northward lift of the subtropical high seems to be the end of the rainy season, the results of the supercomputer simulation are a wake-up call. Simulations show that around July 11, with the southward movement of the westerly cold vortex, the East Asian subtropical high will collapse, and the 5880 line, which represents the range of the subtropical high, will directly retreat to the area of Guangdong and Fujian.
The position of the main monsoon rain belt is closely related to the position of the subtropical high, and the occurrence of this process means that the northerly lifting rain belt may fall southward again, and the south may usher in the second stage of the plum rainy season. This situation is not uncommon meteorologically and is usually associated with the collapse of the subtropical high. The current forecast of the Central Meteorological Observatory believes that heavy precipitation will occur again in the middle and lower reaches of the Yangtze River around the 10th.
The collapse of the subtropical high is an important reason for the formation of the second member of the plum. At present, several numerical models predict that the subtropical high will collapse around July 10, and the southern region may usher in another heavy rainfall process. This phenomenon may have a great impact on residents in Jiangsu, Zhejiang and Shanghai. Especially after a period of high temperature, the sudden change to heavy rainfall will bring great challenges to daily life and production.
Although the phenomenon of inverted yellow plums is not uncommon, in some years it was the trigger for the catastrophic floods, when the cloudy Wuhan finally cleared and the rain bands faded northward on July 6, 1998. The national meteorological station in Wujiashan has measured high temperatures of more than 35 degrees for nine consecutive days, reaching a maximum of 37.7 degrees, and most of the urban area has not fallen for a week. Obviously, the rainy season has ended, and the unique "drought" of the middle and lower reaches of the Yangtze River is gaining momentum.
Wuhan Pass of the Yangtze River, which has just experienced floods, has also begun to take reassurance. Since July 7, the water level in Wuhan has continued to decline; After 11 consecutive days of rainfall, the water surface of the Yangtze River on July 17 has dropped below today's warning level. It seems that the flood of 1998 was an acute one, and although the first wave of the flood peak was unusually ferocious, the overall lack of stamina seemed to be far from being compared with 1954. However, at this time, the subtropical high that controls the Yangtze River basin has begun to retreat.
In normal years, the deputy high dances with the seasons, arrives at the coast of Guangdong in late spring, ascends to Fujian and Taiwan in early summer, controls the Yangtze River basin in midsummer, and even goes as far as North and Northeast China, and then retreats. But 1998 was different, and in the context of the super-strong El Niño of 1997-1998, it was easier to make the deputy high retreat south. Since July 15, the signal of the retreat of the deputy high has been endless, it will go north for a while, and go south for a while, and it will generally retreat in small steps; From July 18, the Central Siberian cold vortex moved southward to the northeast of the continent and stopped. As it spins, it keeps throwing cold air down. Under the continuous harassment, the weakened sub-high finally could not hold on, and on July 20, it trotted all the way back to the Pacific Ocean.
On the night of July 20, cumulonimbus clouds rose in the sky near Wuhan Parrot Island, expanded rapidly like popcorn, and were visible in space during the day on July 21. The humid air flow stirred over Wuhan, climbed sharply for more than ten kilometers, and a huge amount of water vapor turned into a downpour and fell; In the process of rising airflow, a low pressure formed on the ground, attracting more humid airflow to join, and the heavy rain in Wuhan was out of control, and it rained for almost two days and two nights.
At the same time as Wuhan, Huangshi also fell heavy rain, Chongqing, Sichuan, Hunan more and more, scattered rainstorm clouds, they gradually connected and expanded, the plum rain belt formed over the Yangtze River again, the infamous "inverted yellow plum" began. The water level of the main stream of the Yangtze River rose in response, and even bigger flood peaks came one after another, and the water level of Wuhan Pass soared to the sky, heading straight for the highest record in history.
The 7.21 heavy rainstorm in Wuhan was a landmark weather event in the 98 flood fight, and it can even be said to be a turning point. After this heavy rain, the flood of the Yangtze River basin officially occurred. The 7.21 rainstorm in Wuhan tells us that the flood is ferocious, cunning, and an extreme test of endurance. In abnormal weather years, when the heavy rains weaken or temporarily stop, we must not relax our vigilance; Before the summer is over and the monsoon has not left the Yangtze River Basin, we must always pay attention to it. Especially this year, after a few days of northward lifting of the rain belt, there has been a trend of falling southward again, so it is even more necessary to be vigilant, for this complex and changeable weather, we need to pay close attention to the weather forecast and prepare accordingly.
July this year is destined to be an extraordinary month for residents in Jiangsu, Zhejiang and Shanghai. From the rainy season to a multi-day sunny and hot weather to the possible second stage of the plum season, the weather changes not only test our ability to cope, but also remind us to pay attention to the impact of climate change. During this time, staying vigilant, keeping an eye on the weather, and taking the necessary precautions is the best way for us to deal with the complex weather.