August 23rd is the hottest day of the year. A farmer’s proverb says, “Everyone is worried about the rain when it starts to heat up.” What they worry about is the impact of the harvest period.

Sushu introduction:

It is the fourteenth solar term among the twenty-four solar terms and the second solar term in autumn. Dou Zhi Wu (southwest); the sun's yellow longitude reaches 150°; the festival is held on August 22-24 of the Gregorian calendar every year. It's the end of the summer heat, and the "last heat" of the "three heats" of high-temperature and scorching weather has arrived, which means that the hot and unbearable weather has come to an end.

After the end of summer, the direct sun point continues to move southward, solar radiation weakens, and the subtropical high pressure also retreats southward, and the heat gradually subsides. Thunderstorm activity is also less active than in hot summer, and the general trend of heavy rains across the country has weakened. There are many folk activities during summer heat, such as eating ducks, setting off river lanterns, holding a fishing festival, making herbal tea, worshiping the Earth God, etc.

Meteorological changes:

Sushu, which means "out of heat", means that the high temperature will gradually subside. After the summer heat, the direct sun point continues to move southward, solar radiation weakens, and the subtropical high pressure retreats southward. As the height of the sun continues to decrease, the heat it brings also weakens.

The end of the summer season means that the hot and unbearable weather is coming to an end. Although the weather is still hot during this period, it is already on a downward trend. The subsidence of summer heat is a slow process. It does not mean that the weather becomes cooler immediately after the summer heat drops. It usually takes until after the white dew for the real coolness to begin.

After the summer heat, the temperature gradually drops and the temperature difference between day and night gradually increases, but the daytime temperature is still high. The reasons for this phenomenon are: first, the direct point of the sun continues to move southward, and solar radiation weakens; second, the subtropical high pressure retreats southward in a leapfrog manner, and the Mongolian cold high pressure begins to show its strength.

Although the subtropical high pressure has made great strides to retreat southward after the end of summer, it will never give up its dominance and easily retreat to the sea in the Western Pacific. In the southern areas controlled by it, high temperatures are often experienced again at the end of the summer heat. This is the short-term hot weather "autumn tiger".

The length of autumn tiger season varies every year, generally lasting from half a month to two months. The reason for the formation of autumn tiger is that the western Pacific subtropical high pressure that controls China gradually moves southward in autumn, but then moves northward. Under the control of the subtropical high pressure, it becomes clear and cloudy, with strong sunshine and rising temperatures.