GENERAL CIRCULATION OF THE ATMOSPHERE 277 



Asia, and BAGUIOS in the Philippine Islands. This class of 

 storm is usually 300 to 500 miles or more in diameter, with 

 strong or violent winds that circle about the storm center and 

 sometimes blow 100 miles or more per hour. After traveling 

 westward in the tropics, the storm usually curves out into the 

 temperate zone and turns eastward, at the same time gradu- 

 ally becoming broader and less violent. West India hurri- 

 canes occasionally visit the Atlantic seaboard of the United 

 States. Sometimes they enter the Gulf of Mexico and pass 

 northward over the Mississippi or Ohio valleys. Examples 

 of these are the storms that damaged Galveston, Tex., in Sep- 

 tember, 1900, and in August, 1915, and the city of New Orleans 

 in September, 1915. 



The WESTERLIES OF THE TEMPERATE ZONES are turbulent, 

 and full of unequal temperatures, humidities and pressures. 

 The areas, or waves, or surges of unequal pressure are the 

 HIGHS and LOWS that appear on the weather ma>s and control 

 the daily weather of the temperate zone in the manner we have 

 studied. 



303. The Annual Migration of the Sun ; Its Relation to the 

 Weather of Summer and Winter. The entire wind system of 

 the earth is divided into two similar parts by the belt of 

 equatorial calms which is located in the region of greatest heat. 

 As the seasons move north and south with the sun, the entire 

 wind system follows. This annual shift of the wind system 

 indirectly affects the weather of the United States in two 

 important ways. 



1. The tropical hurricanes described in Art. 302 develop in 

 the northern hemisphere principally from August to October 

 and in the southern hemisphere principally from January to 

 April. 



2. Land warms by sunshine more rapidly than water. 

 Therefore, when the sun moves northward in summer, the 

 northern continents become much warmer than the oceans. 

 This develops low pressure over the continents and causes the 

 winds from all sides to blow more or less inward toward the 



