TYPHOON

TYPHOON

The term Typhoon is the regional name in the northwest Pacific for a severe (or mature) tropical cyclone, whereas hurricane is the regional term in the northeast Pacific and northern Atlantic. Elsewhere this is called a tropical cyclone, severe tropical cyclone, or severe cyclonic storm.

Within the northwestern Pacific there are no official typhoon seasons as tropical cyclones form throughout the year. Like any tropical cyclone, there are six main requirements for typhoon formation and development: sufficiently warm sea surface temperatures, atmospheric instability, high humidity in the lower to middle levels of the troposphere, enough Coriolis force to develop a low pressure center, a pre-existing low level focus or disturbance, and low vertical wind shear. The majority of storms form between June and November whilst tropical cyclone formation is at a minimum between December and May. On average, the northwestern Pacific features the most numerous and intense tropical cyclones globally. Like other basins, they are steered by the subtropical ridge towards the west or northwest, with some systems recurving near and east of Japan. The Philippines receive the brunt of the landfalls, with China and Japan being impacted slightly less. Some of the deadliest typhoons in history have struck China. Southern China has the longest record of typhoon impacts for the region, with a thousand year sample via documents within their archives. Taiwan has received the wettest known typhoon on record for thenorthwest Pacific tropical cyclone basin.

Etymology.

The term Typhoon is the regional name in the northwest Pacific for a severe (or mature) tropical cyclone, whereas hurricane is the regional term in the northeast Pacific and northern Atlantic. Elsewhere this is called a tropical cyclone, severe tropical cyclone, or severe cyclonic storm.

The Oxford English Dictionary cites several Oriental words from Urdu (Persian and Arabic) and Chinese giving rise to two early forms in English: (a) touffon (Persian / Arabic) and (b/g) Tuffoons / Tay-fun (Chinese). The Chinese "Tai Fung", is cited as being common dialect forms of ta, meaning big, and fung, meaning wind; in Mandarin 大风 (dàfēng, “big wind”) and in Cantonese 大風 (daai fung, “big wind”). The Persian and Arabic form is from Arabic طوفان (ṭūfān, to turn round), Hindi तूफ़ान (tūfān), and Persian توفان (tufân). Ancient Greek Τυφῶν (Tuphôn, “Typhon, father of the winds”) is unrelated but has secondarily contaminated the word.

CLASSIFICATIONS

A tropical depression is the lowest category that the Japan Meteorological Agency uses and is the term used for a tropical system that has wind speeds not exceeding 33 knots (38 mph; 61 km/h). A tropical depression is upgraded to a tropical storm should itssustained wind speeds exceed 34 knots (39 mph; 63 km/h). Tropical storms also receive official names from RSMC Tokyo. Should the storm intensify further and reach sustained wind speeds of 48 knots (55 mph; 89 km/h) then it will be classified as a severe tropical storm. Once the system's maximum sustained winds reach wind speeds of 64 knots (74 mph; 119 km/h), the JMA will designate the tropical cyclone as a typhoon—the highest category on its scale.

From 2009 the Hong Kong Observatory started to further divide typhoons into three different classifications: typhoon, severe typhoonand super typhoon. A typhoon has wind speed of 64-79 knots (73-91 mph; 118–149 km/h), a severe typhoon has winds of at least 80 knots (92 mph; 150 km/h), and a super typhoon has winds of at least 100 knots (120 mph; 190 km/h). The United States' Joint Typhoon Warning Center (JTWC) unofficially classifies typhoons with wind speeds of at least 130 knots (67 m/s; 150 mph; 241 km/h)—the equivalent of a strong Category 4 storm in the Saffir-Simpson scale—as super typhoons. However, the maximum sustained wind speed measurements that the JTWC uses are based on a 1-minute averaging period, akin to the U.S.' National Hurricane Center and Central Pacific Hurricane Center. As a result, the JTWC's wind reports are higher than JMA's measurements, as the latter are based on a 10-minute averaging interval.

GENESIS

There are six main requirements for tropical cyclogenesis: sufficiently warm sea surface temperatures, atmospheric instability, high humidity in the lower to middle levels of the troposphere, enough Coriolis force to develop a low pressure center, a pre-existing low level focus or disturbance, and low vertical wind shear. While these conditions are necessary for tropical cyclone formation, they do not guarantee that a tropical cyclone will form. Normally, an ocean temperature of 26.5 C (79.7 F) spanning through a depth of at least 50 meters (160 ft) is considered the minimum to maintain the special mesocyclone that is the tropical cyclone. These warm waters are needed to maintain the warm core that fuels tropical systems. A minimum distance of 500 km (300 mi) from the equator is normally needed for tropical cyclogenesis.

...