Why is it so calm on the eve of a typhoon?

The air pressure near the center of the typhoon is low, while the eye of the typhoon is high pressure. Because the air near the center of the typhoon is heated and continues to rise, causing a vacancy below, the space above the eye of the typhoon will drop in time. In addition, the airflow sinks to form high pressure, and areas under high pressure control are calm.

1. The National Meteorological Center is responsible for determining the center position of numbered tropical cyclones, while the center positioning of tropical depressions and tropical disturbances is the responsibility of each provincial (autonomous region, municipality) meteorological observatory.

2. Before a labeled tropical cyclone enters the warning issuing area of ??the National Meteorological Center (that is, east of the 48-hour warning line), it will be positioned four times a day at 00, 06, 12, and 18 hours (Universal Coordinated Time, the same below); when it enters the National Meteorological Center After the warning release area (that is, west of the 48-hour warning line), three additional positionings are issued at 03, 09, and 21:00.

3. The positioning report before each tropical cyclone makes landfall must be issued within 1 hour after the scheduled time. After landing, it can be issued within 1.5 hours after the scheduled time. The meteorological observatory of the province (autonomous region, municipality directly under the Central Government) where the center is located should use it within 1 hour and 15 minutes after the scheduled time. Report center location opinions to the National Meteorological Center by telephone.

4. When a tropical cyclone moves out of the numbered area or the maximum average wind near the center has weakened to level 7 or below and there is no serious weather, the compilation of tropical cyclone live conditions and forecasts will stop. The National Meteorological Center should try its best to communicate with relevant provincial meteorological stations before the suspension. After the tropical cyclone is suspended, meteorological stations at all levels must still strengthen surveillance.

For tropical low pressures that are still located on the islands and mainland of my country after weakening, the National Meteorological Center should continue to compile and publish the location data of the low pressure center until the low pressure disappears. The meteorological observatory of the province (autonomous region, municipality directly under the Central Government) where the low-pressure center is located should provide the National Meteorological Center with center location opinions by phone within 1 hour and 15 minutes after the scheduled time.

5. The National Meteorological Center is not responsible for the timing of positioning. Each provincial (autonomous region, municipality) meteorological station can position itself as needed and notify the relevant meteorological stations in the province (autonomous region, municipality).

6. The landing location of a numbered tropical cyclone will be provided by the meteorological station of the province (autonomous region, municipality) where the tropical cyclone lands within 1.5 hours after the tropical cyclone lands by telephone to the attendant of the consultation room of the National Meteorological Center, and will be coordinated and determined by the National Meteorological Center. The landing point should be at least accurate to the county, and if possible, try to specify the specific location and time. When the telephone line is unavailable, the meteorological station of the landing province (autonomous region, municipality directly under the Central Government) should actively take measures to report. The National Meteorological Center should prepare and issue landing reports in a timely manner.

7. The National Satellite Meteorological Center is responsible for producing and providing tropical cyclone satellite guidance reports. Each tropical cyclone satellite guidance report must be sent within 45 minutes after the scheduled time, and the time of sending is the same as that specified in Article 2.

8. The National Meteorological Center should promptly report tropical cyclone numbering and suspension information to the National Satellite Meteorological Center.