Shulou(Shulou.com)11/24 Report--

In many typhoon information and popular science, an image of the word "typhoon embryo" is often mentioned (correspondingly, in the Atlantic Ocean is hurricane embryo, Indian Ocean is cyclone embryo). Before typhoons were officially named, these "typhoon embryos" had some strange names, such as 93W, 96W, etc., so how did these numbers come from? What's the pattern?

According to the Navy and NOAA, there is a term for "typhoon embryo" called INVEST, and the full word is investigative area, meaning "area worthy of investigation." Other national weather services have similar names, such as tropical disturbance or zone of disturbed weather. "Tropical disturbance" is a common term.

On May 18, Typhoon Ma Wa, the second typhoon of this year in tropical disturbance state, was numbered 92W at that time. It's hard to imagine from satellite imagery and wind fields that it could develop into a super typhoon. A tropical disturbance is an evolution of tropical atmospheric fluctuations. An area where thunderstorm clouds and convergence tend to intensify, where a fuzzy "circulation center" can be seen on the wind and pressure field map, and where the circulation is located in warm seas at low and middle latitudes or even on coastal land, can be called a "disturbance." If the disturbance tends to intensify and may become a threatening tropical depression, the weather agency will number it according to the specific sea area it generates. But with advances in computing power and satellite remote sensing, even weak disturbances that are difficult to develop into tropical cyclones can now be numbered.

The United States Joint Typhoon Warning Center is one of the agencies that issues disturbance numbers. The picture shows the second super typhoon "Mawa" this year, No.02W. At present, because of the need to serve the United States Navy all over the world's oceans, the United States Meteorological Agency's monitoring of tropical disturbances in global seas is relatively complete and systematic. All tropical disturbances with development potential will receive a number from the United States Meteorological Agency, which is often quoted by European institutions and various popular science articles or news.

The numbering rules are roughly as follows: the agency first marks each sea area in the world that may generate tropical cyclones with letters: A Arabian Sea, B Bay of Bengal, E Northeast Pacific Ocean, C Central North Pacific Ocean, W Northwest Pacific Ocean, L North Atlantic Ocean, S South Indian Ocean, P South Pacific Ocean, Q South Atlantic Ocean, M Mediterranean Sea; then according to the order of disturbance generation, it starts from 90 to 99 and then returns to 90, and so on. Since the number of disturbances generated in the same sea area in the same time period is limited, and the disturbance number is temporary, the situation of insufficient number will not occur generally. For example, a disturbance numbered 90W appears one day in the Northwest Pacific Ocean, a new disturbance numbered 91W appears later, and so on until 99W is followed by a new disturbance numbered 90W.

For example, a tropical disturbance 90E generated in the eastern Pacific Ocean, when it crosses 140 ° W and enters the central North Pacific Ocean, will remain 90E as long as it does not strengthen into a tropical depression, and will not become 90C. The number of disturbance numbers has nothing to do with the year, and cycles completely according to the order of generation, because it has a strong temporary nature and will not start from scratch because the year has passed. In the documentation, all disturbance numbers are preceded by the word "invest" to indicate their nature.

Of course, the tropical disturbance is also likely to intensify into a full-fledged typhoon/hurricane/tropical cyclone. When meteorological agencies determine that a tropical disturbance has a relatively clear circulation center and stable development trend, it may be "upgraded" to a tropical depression, that is, the "embryo" can be "born." At this time, the tropical disturbance number is changed to a tropical depression number, becoming an official code.

The letter code for tropical depressions is similar to that for disturbances, except that the letter refers to the area where the system was located when it was upgraded to tropical depression, and not necessarily to the letter in the disturbance code; the numbers are numbered from January 1 of each year, starting with 01. For example, a tropical disturbance generated south of Hawaii (the central North Pacific) is numbered 90C, and when it is upgraded to a tropical depression, it has crossed the 180 ° meridian into the western Pacific Ocean. The maximum number of tropical depressions accumulated in each sea area each year is less than 50, and the tropical depression number (from 01 to 49, there are 49) is never exhausted. When historical data are collected, the low pressure number is distinguished by the year.

How does the name of typhoon come from? (See previous tweets: "Mangosteen, Durian, Jackfruit... How come typhoon naming is so careless?") This is a naming list decided by the Typhoon Committee designated by the World Meteorological Organization. There are 140 names in total, which are named in rotation. To get a name for a typhoon, it needs to be issued by the Japan Meteorological Agency. The Japan Meteorological Agency determines whether a tropical depression meets the naming rules according to the 10-minute sustained wind speed specified by the World Meteorological Organization. The tropical depression is upgraded to tropical storm status when sustained winds reach 35 knots (17.5m/s) in 10 minutes, and the JMA names the storm according to the order of the typhoon naming table. In the western Pacific, tropical depression numbers are unofficial numbers issued by the U.S. Meteorological Agency and do not need to reach tropical storm strength. As a result, there are more numbered tropical depressions per year than officially named storms, and only more tropical disturbances per year that attract the attention of meteorological agencies.

Each area has a dedicated regional centre responsible for tropical cyclone monitoring and signal dissemination. China's Central Meteorological Observatory did not obtain the right to name typhoons, only providing 10 of the 140 names, Hong Kong and Macao can also provide 10 names each. But it is up to the Japan Meteorological Agency to decide whether a typhoon gets a name.

In recent years, U.S. weather agencies have noted that some tropical cyclones may have been modified from extratropical cyclones or "subtropical cyclones," and therefore not only tropical disturbances are numbered, but also extratropical cyclones or subtropical cyclones that may have transition conditions are numbered. For example, North Atlantic Tropical Cyclone Wanda in 2021 was transformed from an extratropical cyclone that swept across the northeastern United States.

In addition to the United States Meteorological Agency, meteorological agencies in other sea areas also issue numbers for their respective sea areas. For example, a low pressure in the northern Indian Ocean would receive an Indian Meteorological Bureau number, a low pressure generated in the Bay of Bengal would be BOBXX (XX stands for two digits), and a low pressure generated in the Arabian Sea would be ARBXX. Australia Meteorological Bureau numbers and names disturbances around Australia. Australia is numbered with the letter U, such as tropical depression 01U, tropical disturbance 11U, etc. Similarly, tropical disturbances in the South Pacific region are numbered F by the Fiji Meteorological Office in the South Pacific. These two agency numbers are official numbers because the two weather offices are regional dedicated centres for these two areas respectively. For these two areas, the numbers from the US Joint Typhoon Warning Center have become unofficial numbers. In addition, the Southwest Indian Ocean Regional Specialized Center is French Reunion, and the French Meteorological Office's Reunion Division will also number tropical depressions in this area, but the French Meteorological Office's number does not have letters, just simple two-digit numbers such as "01" and "02."

All Southern Hemisphere weather agencies are numbered from July 1 to June 30 of each year, and because Southern Hemisphere summer differs from Northern Hemisphere summer by half a year, the timing of the cyclone season is adjusted accordingly. However, the United States Joint Typhoon Warning Center covers the northern and southern hemispheres, so it still counts from January 1 of each year, so there will be a situation where the United States number goes to 15 and the Australia number just starts from 01.

The complete Tropical Disturbance Code letter map (red is the US agency code, purple is the code issued by the Regional Dedicated Center), the meridian used for the division has been marked in the map, the blue dotted line box is the area of Australia, and the orange area is the Fiji Meteorological Office responsibility area. In addition to monitoring typhoons, China will also monitor cyclone storms in the North Indian Ocean. Storms already named by the Indian Meteorological Bureau will be given the number AXX or BXX, such as the first cyclone storm in the Bay of Bengal this year, Mocha, and the Central Meteorological Observatory number B01. China will also temporarily number some tropical depressions worthy of attention. These depressions are often not named, but they can also bring wind and rain disasters. Therefore, there are temporary numbers, such as Tropical Depression 000X in 2022.

To summarize briefly, tropical disturbance numbers are temporary, numbered according to the sea area where they are generated; tropical depression numbers are permanent, numbered according to the sea area where they are transformed into tropical depression and the order in which they are generated in that year. Tropical depressions upgraded to tropical storm class will be officially named, sometimes with corresponding numbers, according to the order and location of tropical storms, such as Typhoon No.11 in 2020, Hurricane No.3 in 2022, Tropical Cyclone No.2 in 2022-23 Southwest Indian Ocean monsoon season, Cyclone No.1 in 2023, etc.

References:

1. https://en.wikipedia.org/wiki/Invest_(meteorology)

2. The National Hurricane Center website https://www.nhc.noaa.gov/aboutgloss.shtml#:~:text=Invest%3A,and%2For%20running%20model%20guidance.

3. JTWC website https://www.metoc.navy.mil/ jtwc/jtwc.html

4. the central meteorological Observatory official website

5. Zoom earth

This article comes from Weixin Official Accounts: Stone Science Popularization Studio (ID: Dr__Stone), author: Sikong

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