11. Typhoon

  1. The origin of the name "typhoon"

    We all know that a typhoon comes with strong wind and torrential rain, and with these it brings terrible damage to people. Victims to typhoon disasters will never forget the severe destruction they have experienced. Yet, what in fact is a typhoon? In terms of meteorology, a typhoon is a tropical cyclone, i.e. a low pressure system developed over tropical seas. As to the origin of the term "typhoon" itself, some say it is from the Cantonese term for "big wind"; yet there is also evidence that it was derived from the Taiwanese term "wind sifter". This is because the pronunciation of the word "sifter" (tai) is identical to that of the word "typhoon". However, no matter where the term came from, it describes a severe storm developed over tropical seas.

  2. Regional origins of typhoon

    Most typhoons that come to Taiwan originate in the western North Pacific Ocean, most frequently from the tropical sea around the Caroline Islands and the Philippines. Sometimes typhoons also originate in the South China Sea; however, they are less frequent and less powerful.

    Taiwan is not the only country in the region affected by typhoons. Japan, the Philippines and Mainland China are also frequently affected. The U.S., India, and even Australia in the Southern Hemisphere also see a lot of tropical cyclones; the difference is that they call them by different names. Tropical storms originating in the Atlantic Ocean are called hurricanes, the term is derived from the Indian (American aboriginal) name of the god of bad weather. Tropical storms originating in the Indian Ocean are called cyclonic storms, which in essence is what a typhoon is.

  3. The classification of the strength of a typhoon

    The strength of a typhoon is classified according to the maximum wind speed at its center:

    i. Tropical Depression: Maximum wind speed at the center equal to or less than 33 knots (17.1 m/s) or scale number 7 on the Beaufort scale.

    ii. Tropical Storm: Maximum wind speed at the center reaches 34 to 63 knots (17.2 m/s - 32.6 m/s) or scale 8 - 11 on the Beaufort scale.

    iii. Typhoon(moderate intensity): Maximum wind speed at the center reaches 64 to 99 knots (32.7 m/s - 50.9 m/s) or scale 12 - 15 on the Beaufort scale.

    iv. Typhoon(intense intensity): Maximum wind speed at the center exceeds 100 knots (51.0 m/s) or over scale 16 on the Beaufort scale.

    A typhoon in the Pacific can happen anytime throughout the year, yet most typhoons happen between July and September. According to typhoon statistics, invading typhoons have come to Taiwan in late April at the earliest, and November at the latest. July, August, and September saw most of the typhoon strikes.

  4. The naming and numbering of typhoon

    In the past typhoons had no name, they were usually numbered according to the sequence of the year, and there was no internationally unified regulation regarding the process. As a result, when there was more than one typhoon at any given time, identification could be very confusing. In light of this, the U.S. Joint Typhoon Warning Center (JTWC) in the territory of Guam started in 1947 to assign names to typhoons for better identification. The naming principles are: for typhoons in the Northern Hemisphere and west of 180°, four groups of alphabetically arranged female names are assigned (21 names in each group, 84 names in total). These names are to be used in circulation throughout. For typhoons in the Northern Hemisphere and east of 180°, separate groups of names are assigned. As for typhoons in the Southern Hemisphere, male names are used. In this way a typhoon can be identified according to the region and time sequence in which it occurs and thus avoid confusion.

    In 1979, the naming principle for typhoons in the western North Pacific was changed. Typhoons were named in male and female name intervals. This naming was again modified in 1990; in addition, two more names were added to each group, increasing the total number of names to 92. In 1996, a four-digit serial number was added to each typhoon. The first two digits represent the year, the last two the sequence of the typhoon in the year. For example, the name "Typhoon 9608 Herb" means that the typhoon Herb occurred in 1996 in the western North Pacific and it was the eighth typhoon of that year.

    In 1998, the World Meteorological Organization decided at the 31st Typhoon Committee in Manila, Philippines that, from the 1st of January, 2000, the unified identification principle of typhoons in the western North Pacific for international aviation and maritime use would be changed, except for the serial number principle (e.g. the first typhoon in 2004 was to be numbered 0401). The old typhoon names would be completely substituted by a newly assigned 140 names (divided into five groups, 28 names in each group). These names were provided by the 14 member states of the Typhoon Committee in the western North Pacific and South China Sea regions. Each nation provided 10 names, which were uniformly arranged by the Regional Specialized Meteorological Center (RSMC) in Tokyo; an organization affiliated with the World Meteorological Organization. However, each nation (or regional administration) was free to choose whether or not to use these names in its weather report.

    Since the new names came from different nations and regions, they included names of local people as well as that of animals, plants, astronomic signs, toponyms, mythical figures, and jewels, etc. And since the sequence was not alphabetical, the name list was complex and irregular. In recent years minor changes concerning pronunciation or translated meanings have been made at each meeting of the Typhoon Committee. The modified names announced in June 2006, were to the two names in Group 3 and the four in Group 4. The latest typhoon names of the region in 2006 are listed in Table 1. There are five columns of names in the list representing 5 Groups, 28 names in each group, which will be used in sequence. The meaning of the tropical cyclone names are in Table 2:

  5. The formation of typhoon

    The air over the tropical seas is warmer due to the heat of sunlight; therefore more sea water is evaporated that makes the air over the tropical seas warm and wet and expands due to its higher temperature, which will in turn reduces its density. This combined with the low wind force in the equatorial region provide a perfect recipe for air upward motion. When the air rises, cooler air from the surroundings will flow in to fill in the space; later this refilling air will be heated and lifted, gradually forming a circulation of air. This process, called convection, will cause the whole column of air to become lighter and lower in density, creating a low pressure system called tropical depression. Since the sun shines directly to north of the Equator during summer, the southeast trade wind from the Southern Hemisphere will be transformed into a southwest monsoon when they pass across to the Northern Hemisphere. When a southwest monsoon meets with a northeast trade wind in the Northern Hemisphere, the two will converge and bring the air upward, enhancing the convection effect. Due to the difference of the wind directions and the nature of the southwest monsoon and the northeast trade wind, they will disturb each other when they meet and create a vortex.

    This kind of disturbance and the convection of the tropical depression complement each other to further deepen the already existing low pressure vortex. In other words, they accelerate the speed of air flow in the surrounding area and the typhoon is initially formed.

  6. The structure of a typhoon

    The size of a typhoon is very large; generally it is two to three hundred kilometers in radius. We can only use circle-like isobaric lines to represent the location and size of a typhoon on weather charts. From satellite photos we can see the top of a typhoon is roughly a round, spiral-shaped whirling cloud. The wind of the typhoon in the Northern Hemisphere will flow in a counterclockwise direction surrounding the typhoon center (while in the Southern Hemisphere it will be in a clockwise direction). From the observation by weather reconnaissance aircrafts that have flown into the typhoon centers from different altitudes and directions, we know that a typhoon is in general, a large cloud column. Its altitude from the top to the ground can vary, with some reaching as high an altitude as 18,000 meters. The center of this huge cloud column, called the eye, is mostly cloudless or with very thin clouds; it is also windless and rainless. Outside the eye, the region nearest to it has the thickest clouds and strongest wind and heaviest rain, which is reduced the further away one moves from the eye.

    The life span of a typhoon would be only one to two days long the shortest. Longer durations can reach two weeks; and average around four to five days from the formation to dissipation of the typhoon. According to statistics there are on average three to four typhoons that pass through Taiwan in a year.

  7. Typhoon warnings

    i. Typhoon sea warning: A sea warning will be issued when the typhoon's radius of sustained winds of 34 knots or greater is anticipated to touch the 100 km sea area of Taiwan, Penghu, Kinmen, and Matsu in 24 hours; and then be renewed every 3 hours. Additional warnings will be announced when necessary.

    ii. Typhoon land warning: A land warning will be issued if the typhoon's radius of sustained winds of 34 knots or greater is going to hit the land of Taiwan, Penghu, Kinmen, and Matsu in 18 hours; and then be renewed every 3 hours. Additional warnings will be announced when necessary.

    iii. Termination of a typhoon warning: A typhoon land warning will be terminated when the typhoon's radius of sustained winds of 34 knots or greater leaves the land area of Taiwan, Penghu, Kinmen or Matsu. A typhoon sea warning will be terminated when the typhoon's radius of sustained winds of 34 knots or greater leaves the coastal area in Taiwan, Penghu, Kinmen or Matsu. The warnings can also be terminated when the typhoon dissipates or changes its direction.

    When a typhoon occurs near the coastal area of Taiwan, Penghu, Kinmen or Matsu, or when the size, speed, and direction of a typhoon has any special change, a sea or land warning, or both when necessary, will be released regardless of the schedule from the preceding paragraphs.

  8. Damage from a typhoon

    The only good thing a typhoon can bring is abundant rain. 60% of summer rainfall in Taiwan is from typhoons, without which Taiwan would be in serious drought. In 1980, when several typhoons passed only nearby and contributed no rain to the region, Taiwan was generally in a drought condition.

    The damage caused from a typhoon, on the other hand, is many. These will be discussed briefly as follows:

    i. Strong wind: Strong wind is the main cause of typhoon damage. A typhoon can cause buildings to collapse, destroy telecommunication or electric circuits, damage crops such as high stem crops, and blow the grain away from rice or wheat.

    ii. Foehn: This condition will wither crops.

    iii. Salty Wind: When the salty sea wind is blown to the land, it will wither crops and can also cause other damage such as electric leakage.

    iv. Waves: Strong winds will bring huge waves. Some typhoon-generated waves can reach 10-20 meters in height. They can cause shipwrecks at sea. Also, long term erosion of the seashore by waves can also cause disasters.

    v. Storm surge: Strong winds cause the sea level to tilt. At the same time low atmospheric pressure will make the sea level rise and cause sea water to flow backward toward land in coastal areas.

    vi. Torrential rain: Destroys crops and floods low-lying regions.

    vii. Flood: Torrential rain in mountain areas will cause a rise in river levels breaking river embankments which will cause floods that will wash out houses, buildings and damage farmlands.

    viii. Landslide: Mountain rocks washed away by torrential rain will tumble, damaging buildings, causing death and injuries of people and animals, and blocking traffic. It often occurs along mountain highways.

    ix. Debris flows: Torrential rain will bring collapsing soil and rock down, which will often cause a river to swell, affecting its course and causing collapsed riverbanks. Accumulation of mud and rocks downstream will also bury roads, buildings, and farmlands.

    x. Disease and pests: Diseases and pests are often found after floods and further damage crops.

    xi. Epidemic diseases: Epidemic diseases, such as the dysentery and cholera, often happen after floods.

  9. Typhoon prevention

    i. Upon receiving a typhoon warning from the Central Weather Bureau via radio or television, you should remain calm, find out whether your home is within the affected area, and carry out typhoon prevention measures as soon as possible.

    ii. Dial 166, 167 weather services hotlines, or keep up with the latest typhoon news from radio or television. You can also use telephone, fax, personal computer or workstation to obtain the latest typhoon news via various channels, such as the Fax on Demand service or from the World Wide Web. However, not to listen to or contribute to hearsay.

    iii. Check the roof, windows, doors, and walls of your homes or buildings before a typhoon arrives. Keep the drainage clear to prevent flooding. Plants should be trimmed or held up by prop stands. Advertisements, signboards and other objects that are hung outside of buildings should be taken down or fastened to prevent from being blown down by strong winds and causing serious damage to buildings, electric wires, animals, and people.

    iv. Prepare radio, emergency lighting, candles, matches, and a three day supply of food, water, and fuel in case of power or water cuts and temporary shortages of food. Furthermore, you should check electric circuits before the typhoon arrives; during typhoons you should also shut off gas lines to stoves in your home to prevent fires.

    v. After a typhoon sea warning is issued, all vessels operating at sea or onshore should carry out typhoon prevention measures. Listen to the Taiwan Fishery Broadcast radio station or Fishery Broadcasts in Keelung and Kaohsiung or other radio stations for the latest typhoon news.

    vi. After a typhoon land warning is issued, residents in low-lying, coastal or mountainside areas should move to a safe place as soon as possible, to prevent possible injury from storm surge, flooding, landslides, debris flow or collapse of buildings.

    vii. Stay indoors during the typhoon.

    viii. When the eye of the typhoon passes over, the wind and rain will subside. Don't assume that the typhoon has left and go outside, because heavy storms will return after a short time.

    ix. When electric wires are blown down by strong winds they may cause extremely dangerous sparking and electric shock, therefore report these to the power company for emergency repair.

    x. When it is within your capability, please help to rescue injured people or trapped children and women. If it is beyond your capability, contact police or other civil defense units for help immediately.