Hurricane Trajectories 



From the accumulated records it appears that a large number, and 

 probably a majority, of Mexican west-coast hurricanes are first reported 

 from the eastern Pacific at about lat. 15° N. ; long. 100° W. Backward 

 extrapolation of their trajectories suggests quite strongly that they 

 have a common area of origin somewhere in or near the Gulf of Darien, 

 an arm of the Caribbean between Panama and Colombia. 



Stud}' of a number of these trajectories shows that these storms, 

 near their suspected area of origin, are usually relatively small cyclonic 

 disturbances, which do not become full-fledged tropical cyclones until 

 they have travelled for some distance. A few of the disturbances cross 

 the Isthmus of Panama, usually as strong to violent families of squalls ; 

 more travel northward, on the Caribbean side of the isthmus, gaining 

 violence en route, and cross to the Pacific via the Rio San Juan-Lake 

 Nicaragua gap. In this area they are usually, but not invariably, recorded 

 as strong cyclones, but with winds still considerably below hurricane force. 



It is usually not until these cyclones have travelled for several hundred 

 miles over the Pacific that they acquire maximum violence and true 

 hurricane characteristics. 



Although a few of these tropical cvclones acquire trajectories in the 

 general direction of Clipperton Island (lat. 10° 17' N. ; long. 109° 13' W., 

 approximately), and a few others appear to originate in that vicinity, 

 most of these storms travel roughly parallel to the west coast of Mexico, 

 a few hundred miles off shore, from about long. 100° W. (south of 

 Acapulco) to about lat. 20° N. (west of Cabo Corrientes), few reported 

 hurricanes going far west of the Revilla Gigedo Islands (^). 



After passing the Tres Marias Islands (lat. 21° 19' N. ; long. 106° 

 18' W., approximately), usually to the west, many of the hurricanes 

 recurve, and run ashore on the mainland of Mexico, in the States of 

 Sinaloa or Sonora. A few proceed up the Gulf of California to the mouth 

 of the Colorado River, and enter the United States near Yuma (about 

 60 mHes up the Colorado River, in lat. 32° 46' N. ; long. 114° 38' W.), at 

 the junction of the Gila and Colorado Rivers, in Arizona. 



Other hurricanes continue farther northwestward, eventually con- 

 tacting the west coasts of Baja California (Mexico) or of (x-\lta) California 

 (U.S.A.). 



About one-third of the reported tropical cyclones in this area are lost 

 at sea somewhere between latitudes 20° N. and 40° N., little or nothing 

 being known of their trajectories north of the Revilla Gigedo Islands. 



Trajectory Controls 



Hurricanes, according to current theories, which are now regarded as 

 somewhat incomplete, but which contain substantial elements of correct- 

 ness, are vortical atmospheric disturbances, maintained by the continuing 

 release of the heat of vaporization of the atmospheric moisture carried 

 aloft and condensed to liquid water. In accord with this generalization, 



(1) A cluster of uninhabited volcanic islands, surrounded by coral and numerous 

 "obstructions to navigation," at about lat. 18° 50' N. ; long. 112° 40' W. The 

 largest island, Isla Socorro, is a coffin-shaped mass of volcanic material (Pliocene ?) 

 about eight by twenty-four miles, with a maximum height of about 4,000 ft. The 

 entire group rises from a subsea platform, probably about 2-50 ft. below the present 

 sea surface. 



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