Typhoon What are Hurricanes and Typhoons? What causes typhoons? What is a hurricane, typhoon, or tropical cyclone? Where do hurricanes occur / form? What are Hurricanes and Typhoons? Hurricanes and typhoons are both types of storms with great power and strength that cause extensive damage. They can tear apart entire cities with their powerful wind and strong storm surges. The region where the storm occurs determines whether it is called a hurricane or a typhoon. Hurricanes usually begin off the coast of Africa and travel across the Atlantic Ocean. Typhoons normally originate in the northwest part of the Pacific Ocean. When in open waters, a tropical storm can last for more than two weeks. Hurricane season is from June 1 until November 30. The majority of typhoons form between May and December in the United States. In order for a tropical storm to be classified as a typhoon, the storm must reach wind speeds of 65 knots (70 mph). Typhoons are measured on the RSMC (Regional Specialized Meteorological Centre) Cyclone Intensity Scale. Hurricanes are measured on the Saffir-Simpson scale, which was invented in 1971 by Herbert Saffir and Bob Simpson. This scale divides hurricanes into five categories. The classifications are categories 1, 2, 3, 4, and 5. In order to be classified as a hurricane or typhoon, the storm must have a minimum wind speeds of 74 mph. Any storm with winds less than 74 mph can be categorized under tropical storm or tropical depression. The following are the five categories: hurricane rotating * Category 1 hurricanes have wind speeds of 74 - 95 mph. * Category 2 hurricanes have wind speeds of 96 - 110 mph. * Category 3 hurricanes have wind speeds of 111 - 130 mph. * Category 4 hurricanes have wind speeds of 131 - 155 mph. * Category 5 hurricanes have wind speeds greater than 156 mph. Hurricanes and typhoons form in warm ocean waters. The warm water is the source of the storm’s energy. Therefore, the warmer the water, the more energy and power the storm obtains. As soon as the storm makes landfall, it begins to lose strength. All hurricanes and typhoons have a center point around which it circulates, hurricane destuctioncalled the “eye”. If the storm has enough power and strength, it can develop a large eye in the center. Weather in the eye is usually very calm. Hurricanes and typhoons can produce a number of problems. The effects could include treacherous rain, huge waves, storm surges, strong wind, and much more. Hurricanes and typhoons are known to flood streets, destroy homes, blow down trees, and kill people. Much of this could be prevented if people were more aware of how to be prepared to survive the effects of a hurricane or typhoon. If one lives where hurricanes or typhoons could make landfall, especially on the coast, one should have an emergency evacuation kit. Pre-conditions for typhoons Several atmospheric ingredients must come together for a typhoon to form. Since a typhoon is just another term for hurricane, the same conditions apply for both. There are perhaps seven atmospheric conditions which, if met, could cause a typhoon to form. A pre-existing disturbance, warm ocean water, low atmospheric stability, sufficient Coriolis force, moist mid-atmosphere, and upper atmosphere divergence are all important factors for typhoon formation. These conditions are discussed in greater detail in Tropicalweather.net's "How do hurricanes form?" These factors are important in that tremendous amounts of heat energy is transported from the tropics northward to the higher latitudes. The typhoon is a large heat engine, where great amounts of heat are being produced from the process of latent heat of condensation. This occurs as water vapor is being evaporated from the ocean surface and condensed into cloud droplets. Mechanisms to cause typhoon Formation If all of the pre-conditions are met, typhoon formation then becomes possible. There are several types of atmospheric disturbances that can cause a typhoon to develop. The most common mechanism to cause a typhoon to develop is the monsoon trough. This is an extension of the Inter-Tropical Convergence Zone where cyclonic spin has developed. The ITCZ is a trough of low pressure created by the convergence of the northeast and southeast trade winds. This "trade wind" trough does not contain the spin to initiate typhoon development. Typhoon ( hurricanes ) are caused mostly by the monsoon trough in six of the seven hurricane / typhoon formation basins of the world. Another cause of typhoon formation is from the Tropical Upper Tropospheric Trough (TUTT). The upper air low is cold in nature as compared to its surrounding environment. A typical low pressure center that forms a typhoon starts at the lower levels and is warm compared to its environment. If a TUTT low remains over the warm ocean waters for several days, sometimes it gradually warms and takes on tropical characteristics. At this point the low "reaches" down to the surface from the upper atmosphere where the development process transforms. Another cause of typhoon development is from a front which stalls over tropical waters. Inherently, a front has a cyclonic spin associated with it. If winds aloft become favorable with little wind shear, showers and storms could become more numerous and cause a typhoon to form. By far, the monsoon trough causes most typhoons to form in the western Pacific Ocean. What is a hurricane, typhoon, or tropical cyclone? Where do hurricanes occur / form? Hurricane and tropical cyclone formation basins Where do hurricanes occur? Hurricanes or tropical cyclones form in seven distinct basins around the world. Some hurricanes formation basins are much more active than others. Some tropical cyclone basins also have a much longer time frame in which tropical cyclones may occur during the year. Most tropical cyclones form from a disturbance in the monsoon trough. The north Atlantic basin is considerably different, as the majority of hurricanes form from easterly waves originating from Africa. Hurricanes and typhoons only can form over large basins of warm water such as an ocean or sea. This is due to the fact that they need a large amount of energy which is supplied by the heat from the warm ocean waters evaporating into the atmosphere. Hurricanes also occur at least several degrees away from the equator. This is because the Coriolis force is too weak at the equator to generate spin for the hurricane. North Atlantic Ocean Hurricane season: June 1 - November 30. The most active period runs from about mid August through the latter part of October. Locations that may be affected are the Caribbean, Bermuda, Central America including eastern Mexico, the eastern and Gulf coasts of the United States, and eastern Canada. Eastern North Pacific Ocean Hurricane season: May 15 - November 30. This is the second most active region for tropical cyclones in the world. These storms mostly move into the open eastern Pacific Ocean but can affect western Mexico and sometimes after developing, Hawaii. Northwest Pacific Ocean Typhoon season: All year. This is the most active basin in the world. Most typhoons form between July through November. The tropical cyclones that form here can affect the Philippines, southeast Asia including China and Taiwan, and Japan. Bay of Bengal / Arabian Sea Severe Cyclonic storm season: April 1 - December 30. This basin has a double maximum because of the monsoon trough moving through at two different times of the year. Maximums occur from mid April through May and from mid September through mid December. Southwest Pacific Ocean Severe Tropical Cyclone Season: October 15 - May 1. These tropical cyclones may affect eastern Australia. Southeast Indian Ocean Severe Tropical Cyclone Season: October 15 - May. These tropical cyclones may affect northern and western Australia. This basin has a double maximum in mid January, and mid February through early March. Southwest Indian Ocean Tropical Cyclone Season: October 15 - May 15. These tropical cyclones may affect Madagascar and southeastern Africa. A double maximum occurs in mid January and mid February through early March.