northwesterly, then a northerly, track. Continuing to curve to the right, it eventually heads to the northeast. It is possible that at this point its speed will increase, which accounts for the usual path of hurricanes that originate in the Atlantic Ocean near the Cape Verde Islands, North Africa, and track into the Caribbean and the southern United States, as well as those that originate near southern Mexico and track into the Pacific Ocean toward Hawaii, moving around the Pacific High. In the southern hemisphere, after traveling west initially, hurricanes recurve to the southwest and then the southeast. There is no assurance that hurricanes will always follow these paths; there are many exceptions where they have plowed straight west or northwesterly, the Galveston storm in 1900 being an example. The direction of hurricanes is frequently altered by encountering high-altitude winds. Once they reach colder land or water, they lose water and energy and dissipate.


The life cycle of a hurricane as viewed from an endangered vessel at sea starts at the bridge, where the captain observes that the barometer has fallen several millibars in the last 20 hours. Weather reports indicate a tropical disturbance moving westward toward the vessel at 10 knots. Shipboard instruments show that the seawater temperature is 29 degrees Celsius (84 degrees Fahrenheit). The sudden drop in atmospheric pressure is significant; when combined with the sea temperature it indicates a tropical storm is possible. The captain contacts the National Hurricane Center by radio and receives the latest satellite photographs.12

The storm is now classified as a tropical depression. The satellite photos show the characteristic spiral pattern of clouds, extending out 100 nautical miles with a central pressure down to 990 millibars. Subsequent reports from the National Weather Service indicate maximum winds of 80 knots; the central pressure has dropped to 980 millibars.

The captain makes a sharp turn to the northeast, since his vessel is on the right side of the forward track of the storm. He observes that seas have built to 33 feet. He keeps the wind on his starboard bow and makes as much way as possible at 16 knots, hoping the storm does not

The National Academies | 500 Fifth St. N.W. | Washington, D.C. 20001
Copyright © National Academy of Sciences. All rights reserved.
Terms of Use and Privacy Statement