When the tropical cyclone intensity reaches what level, the meteorological department will name the typhoon according to the typhoon naming table and at the same time

When the intensity of a tropical cyclone reaches a high level, the meteorological department will be ordered to name the typhoon.

The movement of typhoons is mainly controlled by the guiding airflow. In a sense, the problem of forecasting the movement path of typhoons is mainly the problem of forecasting the guiding airflow of Typhoon. Forecasting the movement path of typhoons in the western Pacific mainly focuses on the positions and intensity changes of the Pacific subtropical high and westerly ridges. The direction of the typhoon after it moves westward past 140°E is the focus of our actual forecast.

(1) Focus on forecasting westward-moving typhoons. Westward-moving typhoons mean that typhoons have been pulled by easterly airflow and enter the South China Sea or land in Guangdong or Vietnam. The common situation is that the subtropical high pressure is strong, the long axis is an east-west ridge, and is stable between 25-30°N. There are subtropical high pressure centers in southern Japan and the middle and lower reaches of the Yangtze River in my country. There is a subtropical jet stream and a relatively straight frontal area on the northern edge of the subtropical high, or there are only some fast-moving small troughs. The typhoon is in a stable easterly airflow on the southern edge of the subtropical high.

(2) Focus on turning to the typhoon forecast

When the typhoon moves from the east wind into the westerly belt, controlling the direction of the air flow from east to west will promote the typhoon's turn. The common weather situation is a meridional circulation with a stable long-wave trough or a developing low trough along the eastern coast of my country, with the bottom of the trough extending and stabilizing at lower latitudes. The subtropical high in the Pacific often retreats eastward and weakens, or breaks off at the longitude where the typhoon is located. At this time, the typhoon can easily enter the westerly belt from the southwest edge of the subtropical high around the ridge line of the subtropical high pressure, or go northward from the rupture of the subtropical high pressure into the westerly belt, and then turn in the southwest airflow in front of the westerly trough.

(3) The focus of northwest-moving typhoon forecast is that the typhoon moves northwestward under the control of stable and deep southeastern airflow. Often land in Zhejiang and Fujian areas. The characteristics of the situation are that a long-wave trough appears in the westerly belt at 70°~90°E, and the eastern coast of my country is controlled by a long-wave ridge. The subtropical high centered in the Yellow Sea and the Sea of ??Japan is on the south side of the stable long-wave ridge, and there is constant warm advection. It is supplemented or merged with a warm high in the west that moves eastward and develops very strongly. The axis of the subtropical high moves northwest to southeast. At this time, the typhoon was controlled by the southeastern airflow on the south side of the subtropical high, landed in Zhejiang and Fujian from the front, and penetrated deep into the inland and filled up.

There are two paths for a typhoon after it makes landfall: one is to go westward, and the other is to turn. This depends on the conditions of the subtropical high and westerly trough as well as the typhoon itself.

Other methods for forecasting typhoon movement paths

Synoptic methods, statistical methods, dynamic methods, statistical-dynamic methods, and numerical forecasting [3].

Difficult paths of typhoons

Sudden eastward bends, sudden westward turns, northward bends, twisting and serpentine paths, and double typhoon paths.

The formation and development of typhoons

Necessary conditions for the occurrence and development of typhoons

(1) Thermal conditions

The vast warm sea surface, the The temperature is above 26-27℃.

(2) Initial disturbance

Due to the upward motion caused by frictional convergence, the air parcel can be lifted above the height of free convection, thereby releasing unstable energy. ITCZ disturbances account for 85%, easterly waves account for 10%, and mesoscale cutoff low pressure and high-altitude cold vortices account for 5%.

(3) The effect of a certain geostrophic deflection force

It can gradually form the convergent airflow into a strong counterclockwise rotating horizontal vorticity.

(4) The vertical shear of the wind speed in the troposphere should be small

The vertical shear of the wind speed in the middle troposphere should be small, so the relative movement of the air above and below the troposphere is very small; and the latent heat released by condensation is always Heating the same air column within a limited range can quickly form a warm center structure; ensuring that the initial disturbance of air pressure continues to decrease rapidly, and finally forms a typhoon.

Typhoon occurrence and development mechanism

The second type of conditional instability theory (CISK): Cumulus convection releases condensation latent heat, which continuously warms the middle and upper troposphere and increases the upper air pressure. , producing divergence. High-level divergence in turn causes the air pressure at the low-level disturbance center to decrease, resulting in convergence. This large-scale low-level convergence provides water vapor for the development of cumulus convection. This cycle leads to the continuous development of disturbances and the formation of typhoons. The instability caused by the interaction between cumulus convection and sky-scale disturbances is called the second type of conditional instability (CISK).

Initial disturbance of typhoon formation

(1) Vortex in ITCZ ??(85%) Four-stage model of typhoon generation

(2) Tropical wave disturbance (10%)

Three-stage model: fluctuation stage; warming stage; development stage

(3) Mid-latitude cutting off cold vortex

(4) Tropical high altitude Cold vortex

External synoptic conditions for the occurrence and development of typhoons

(1) Impact of cold air: Strong cold air weakens typhoons, or prevents tropical depressions from developing into typhoons; if the cold air strengthens The convergence effect of low-level tropical disturbances.

(2) Flow field in the middle troposphere (subtropical high)

(3) Anticyclonic flow field in the upper troposphere (South Asian High)

(4) Relationship with high-altitude jet streams

The demise of typhoons

(1) Disappearance: After a typhoon makes landfall, the water vapor decreases, and the typhoon will weaken rapidly and eventually disappear completely.

(2) Become an extratropical cyclone.

Typhoon weather

(1) Typhoon rain

Heavy rain caused by the typhoon itself; interaction with westerly belts and tropical weather; heavy rain caused by terrain (typhoon landing) (previously)

(2) Strong winds

Typhoon wind speed is very gusty, and the difference between its instantaneous maximum wind speed and minimum wind speed can reach more than 30 meters/second. Generally, the wind speed distribution relative to the center of the typhoon is asymmetric and is related to the surrounding air pressure situation.

(3) Storm surge, long wave, hurricane wave, swell, tide. The sudden surge in sea water caused when a typhoon makes landfall is often called a typhoon surge.