AEROGRAPHER'S MATE 3 & 2 



exceeds any other phenomena in total damage 

 and loss of life. 



Tropical cyclones have been given names 

 in different regions of the world, such as, 

 "Hurricane" in the Atlantic and eastern North 

 Pacific areas; "Typhoons" in the western North 

 Pacific areas; "Willy-Willies" in Australia; 

 and "Baguios" in the Philippines; however, 

 they all have essentially the same characteristics. 

 Although the tropical cyclone normally covers 

 a large area, roughly circular or elliptical 

 in shape (fig. 14-26), it is usually of small 

 size compared with large extratropical cyclones. 

 It differs also in that there are no distinct 

 cold and warm sectors and no well-defined 

 surfaces of discontinuity or fronts at the sur- 

 face while the cyclone is in the Tropics, The 

 tropical cyclone is found most frequently in 

 summer or autumn of the hemisphere in which 

 it occurs, while the extratropical cyclone is 

 most frequent in cold months. Tropical 

 cyclones have no moving anticyclones as com- 

 panions while in the Tropics. In many other 

 features, such as the region of calm or relative 

 calm called the "eye," the east to west 

 component of progressive motion in its early 

 history, and the distribution of rainfall, tropical 

 cyclones are distinctive. However, on leaving 

 the Tropics they take on some of the charac- 

 teristics of extratropical cyclones. 



Classification of Tropical Cyclones 



The nomenclature of tropical cyclones varies 

 considerably. At times such terms as "tropical 

 cyclone," "tropical storm," "typhoons," and 

 "hurricanes" are used almost interchangeably 

 with little regard for differences in size or 

 intensity. There are generally three recognized 

 categories of nonfrontal cyclones of tropical 

 origin, all of which must show evidence of a 

 closed circulation at the surface. These are 

 distinguished in terms of observed or estimated 

 surface wind speeds associated with the systems 

 as follows: 



209.77.1 

 Figure 14-26, — Satellite pictures of tropical 

 cyclones in the Atlantic Ocean showing their 

 unique circular shape. 



1. Tropical Depression. Maximum winds less 

 than 34 knots and one or more closed isobars 

 on the surface. Normally these are expected 

 to intensify. 



2. Tropical Storm. Closed surface isobars 

 with maximum winds 34 to 63 knots, inclusive. 



3. Hurricane/Typhoon. Maximum winds of 

 64 knots or higher. 



Life Cycle of the Tropical Cyclone 



The energy that sustains tropical cyclones 

 is derived from the energy that is released 

 through the latent heat of condensation. The 

 energy source is furnished to the tropical 

 storm by the warm water sources over which 



340 



