Why is Typhoon Prasang moving so fast? Will it be the heat terminator?

Zhejiang Weather released the latest news at 11:00 on September 19. The center of this year's 14th typhoon "Prasang" (strong tropical storm level) was located on the sea about 320 kilometers east of Xiangshan at 10:00 today, that is, 28.8 degrees north latitude and 125.1 degrees east longitude. The maximum wind speed near the center was level 10 (25 meters/second), and the lowest central pressure was 985 hPa.

It is expected that "Prasang" will move rapidly toward the northwest at a speed of 40 to 45 kilometers per hour, gradually increasing in intensity, and make landfall on the coast of Zhoushan and Ningbo this afternoon or evening (tropical storm level or strong tropical storm level, level 9 to 11, 23 to 30 meters per second), and then gradually weaken.

Why is Typhoon Prasang moving so fast?

On average, a typhoon moves between 15 km/h (4.17 m/s) and 20 km/h (5.56 m/s). A speed of 30 km/h is considered fast among typhoons. However, the Typhoon "Prasang" heading towards Zhejiang is a "speedster", running 1,100 km in a single day. Its speed yesterday reached an astonishing 60 km/h, which is four times the speed of Typhoon "Makar".

In everyone's impression, the faster a typhoon moves, the stronger it is. In fact, this is not necessarily the case. For example, the 2014 Super Typhoon Rammasun moved at a speed of 5 km/h to 10 km/h. Another example is the 2018 Typhoon Ewiniar, which moved northward at a speed of only 10 km/h after forming a tropical depression over the South China Sea.

Why do some typhoons move fast while others move slowly? According to experts from the Central Meteorological Observatory, the movement of typhoons is mainly affected by large-scale guiding airflows. Take Typhoon Ewiniar as an example. At that time, the typhoon was generated on the south side of the subtropical high pressure. During its generation and approach to southeastern Hainan, the subtropical high pressure was in the stage of eastward movement and weakening. The distance between the typhoon and the subtropical high pressure increased, causing its guiding airflow to weaken and its movement speed to slow down. Even a strong typhoon will not move fast if it encounters a weak guiding airflow, or if there are opposite systems "saddle fields" on both sides that start a tug-of-war with it, or if multiple typhoons rotate against each other.

A weak typhoon does not mean a small impact

Compared with this year's super typhoon "Makar" and the recent strong typhoon "Bebejia", the current tropical storm-level typhoon "Prasang" sounds a bit weak. But a weak typhoon does not necessarily mean a small impact, so don't take it lightly.

Although statistically, stronger typhoons tend to bring more precipitation, sometimes, those seemingly loosely structured and inconspicuous weak typhoons can also bring terrible impacts once they encounter the right time and place. For example, when Typhoon Wipha landed in my country for the first time in 2019, its intensity was only tropical storm level, with the maximum wind speed near the center of 23 meters per second. However, it lingered along the southern coast of my country for three days and three nights, dumping hundreds of millimeters of precipitation in Hainan, Guangdong, and Guangxi, causing serious impacts such as urban waterlogging, mountain torrents, and mudslides.

According to the news released by Zhejiang Weather at noon today, the heavy rain of "Prasang" is "strong in spots and scattered in areas". There is a medium to high risk of heavy rain disasters in coastal areas and parts of the northwestern mountainous areas. The public should pay attention to prevent secondary disasters such as urban and rural waterlogging, mountain torrents in small watersheds, and landslides caused by local heavy rainfall. In addition, it is still necessary to guard against the adverse effects of strong winds of 8 to 11 along the coast.

Will "Prasang" be the terminator of high temperatures?

On the other hand, the long-awaited drop in temperature is finally coming.

The high temperature weather since August this year is likely to be ended by Typhoon Prasang, because it not only exerts its own power, but also borrows the power of cold air. It is expected that a new round of cold air will begin to affect our province on the 20th, and Zhejiang will begin to cool down from north to south, starting from the 20th in northern Zhejiang and the 21st in central and southern Zhejiang.

The typhoon and cold air will strike hard against the "autumn tiger", with a temperature drop of 4-6℃. Starting from the 22nd, the effect of this round of cooling will gradually become more noticeable. For example, the highest daytime temperature on the 23rd will drop below 25℃ in many areas.

There will be more rainy days. As the subtropical high retreats eastward, cold air and warm and humid air currents will confront each other in East China. From the 21st to the 25th, most parts of our province will have more precipitation, so everyone should prepare rain gear in advance.