324 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1956 



when there are orographic features that cause air in advance of the 

 storm to flow upslope; or when there is a dense air mass several 

 hundred miles in advance of the storm, which acts as a wedge for 

 the warmer moist air around the hurricane to flow up and over. 



L. Hughes [10], using mean wind data for a number of tropical 

 storms, after making reasonable assumptions about the amount of 

 moisture that would be carried into storms at low levels, computed the 

 intensity of rainfall that should be expected in hurricanes. The values 

 computed by him are such that if a hurricane passed directly over a 

 station while moving in a straight line there would be a total rainfall 

 of about 11 inches in 48 hours. This appears to be a reasonable value. 

 Cline [2] and other investigators have found 8 to 10 inches occurring 

 frequently under similar conditions in the Atlantic and Gulf storms. 



5. FORECASTING FLOODS ASSOCIATED WITH HURRICANES 



The problems associated with forecasting floods from hurricane 

 rains may be summarized as: (1) Forecasting the path the hurricane 

 will take; (2) the distribution of rainfall around the hurricane; (3) 

 the effect on the rainfall of upslope motion caused by the air in ad- 

 vance of the hurricane flowing up over a mountain or up over a colder 

 denser air mass; (4) the amount of runoff that will follow the rain- 

 fall; (5) the rate of movement of the hurricane ; and (6) the intensity 

 of rainfall associated with the hurricane and the various upslope mo- 

 tions given to the air mass in advance of the hurricane. 



A good illustration of the necessity for forecasting the amount of 

 runoff to be expected occurred in the 1955 season. Hurricane Connie 

 gave as much rain as hurricane Diane in some of the areas that were 

 afflicted by the death-dealing floods following the passage of Diane. 

 In general, however, the floods following Connie were not very dan- 

 gerous. The rains from Connie did, however, almost completely satu- 

 rate the ground. When Diane followed soon after, nearly all the rain 

 that fell was available for runoff and the excess water soon caused 

 mountain streams to rise above the banks and to sweep everything 

 before them. 



6. STORM SURGE 



The storm surge is the greatest killer and greatest property de- 

 stroyer associated with hurricanes. In areas where hurricane building 

 codes have been rigidly enforced for many years, relatively little dam- 

 age is done by hurricanes to buildings away from the waterfront. 

 Even hurricane Janet at Chetumal, Mexico, in 1955 did relatively little 

 damage to solidly constructed concrete houses. In areas near the coast 

 that are exposed to the storm surge, the force exerted is almost irre- 

 sistible. Recorded history of tropical cyclones reveals many instances 

 of cities and towns being inundated. At Santa Cruz del Sur, Cuba, in 

 November 1932, approximately 2,500 lives were lost out of the total 



