250 A.'N-NUAL REPORT SMITHSONIAN INSTITUTION, 19 3 9 



HURRICANE HAZARDS IN NEW YORK AND NEW ENGLAND 



The conditions under which a West Indian hurricane will strike 

 our North Atlantic coast with full vigor are that (1) the general 

 pressure gradient from east to west must be great throughout the 

 troposphere; (2) the terrain in front of the storm must be well 

 bathed in moist tropical air; and (3) the storm remains over the open 

 sea all the way from the West Indies to its northern landfall. With- 

 out the rapid progressive movement the storm would have a chance 

 to lose much of its whirling velocity over the cooler waters north 

 of the Gulf Stream. The presence of moist tropical air over the 

 region helps to prevent a too rapid reduction in energy. Friction 

 with the land is a quick reducer of the velocity of the wind at the 

 surface, causing a decrease in both the deflective effect of the earth's 

 rotation and the centrifugal force of the whirling wind. This results 

 in a considerable flow of air across the isobars into the low-pressure 

 center and, consequently, in a marked reduction of the pressure 

 gradient, which is immediately felt on all sides of the storm. In 

 order to have one of these hurricanes strike the North Atlantic coast 

 from the open sea it is, of course, first necessary that the general 

 winds in the middle levels of the troposphere shall be directed essen- 

 tially northward or perhaps northwestward, so as to give the storm 

 a movement from the south or from the southeast. 



In terms of the hazards to New York City this is a very fortunate 

 circumstance ; for not only is New York protected by the New Jersey 

 coast on the one side and by Long Island on the other, but also the 

 chances of the storm's coming from the southeast are slender. Never- 

 theless, a high storm tide can reach New York, even if surf and the 

 strongest winds from the open ocean cannot. If such a storm tide 

 should coincide with high spring tide and the Hudson in flood, lower 

 Manhattan and its subway entrances might be inundated suddenly. 

 In 1821 the tide rose 13 feet in 1 hour as a hurricane center passed 

 over New York; in 1938 it rose about 6.9 feet in half an hour when 

 the storm center passed into central New England. 



Other lessons taught by this catastrophe are: That the North 

 Atlantic States should have a hurricane observing and warning serv- 

 ice equal to that of the South ; that especial attention should be paid 

 to cloud motions, to be observed and reported whenever visible, as 

 indicators of the direction and velocity of the middle and upper 

 levels of the air stream in which a hurricane may be traveling; that 

 the network of radiometeorograph stations for deep soundings of 

 the temperature and humidity of the atmosphere be extended to 

 include the northeastern States, so that the potential energy available 

 for the storm can be computed and weather maps for levels aloft can 

 be drawn and winds computed when not observable through low 



