An intense look at Haiyan As the Super Typhoon Haiyan, heads towards Vietnam after causing massive destruction to the Philippines on Friday, we look at what causes these storms and how can we determine there intensity. Super Typhoon Haiyan (the Chinese name for the petrel sea bird), or Typhoon Yolanda as it is locally known in the Philippines, has been the strongest tropical cyclone of 2013. It is also one of the most powerful cyclones on record to ever make landfall, resulting in widespread damage. The storm has already destroyed vast amounts of buildings, triggered landslides and caused severe loss of life. Super Typhoon Haiyan first battered the islands of Samar and Leyte with winds of more than 300km/h (186mph) and a storm surge that inundated coastal villages. The storm then intensified before making landfall on the Philippines shortly before dawn on Friday, bringing gusts that reached 379 km/h (235 mph), with waves as high as 15m (45ft), bringing up to 400mm (15.75 inches) of rain in places. A typhoon is defined as a mature tropical cyclone that develops in the western part of the Pacific Ocean between 180°E and 100°E. This region is often referred to as the northwest Pacific basin. There are a number of conditional requirements for tropical storms to form (tropical cyclogenesis). There needs to be 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. However, even though these conditions are necessary for tropical cyclone formation, they do not necessarily guarantee that a tropical cyclone will form. Once a tropical cyclone has formed the most important question is how intense it is and how intense will it become. There are several tools and techniques to estimate the intensity of a tropical cyclone, including subjective estimates, objective fix data, and observations. A super typhoon is simply defined as cyclone in which the wind speeds above 241 kph (150 mph) and is equivalent to a category 4 Hurricane. However, one of the primary means of estimating tropical cyclone intensity is not just the wind speed but the subjective Dvorak technique. The Dvorak technique was developed by Vernon Dvorak between 1969 and 1984. The technique uses the analysis of cloud patterns in visible and infrared imagery from geostationary and polar-orbiting satellites. The satellite images are analysed against several visual patterns that a cyclone may take. Each pattern is shown in the diagram. These patterns define the upper and lower bounds of the intensity of the cyclone.
Posted on: Sat, 09 Nov 2013 17:54:48 +0000
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