STORM.S AND WEATHER FORECASTS Hi 



heavy ocean swell may be caused by tbe friction of the rajiidlv 

 gyrating air on the surface of the water, and when the iiurricane 

 has a slow progressive movement tiiis swell may be propagated 

 outward from thecenter of the storm faster than the storm is mov- 

 ing and reach the coast several hours before either the Ijarometer 

 or the wind movement gives any indication of the coming storm. 



The tracks of West India hurricanes are alwa3's in the form 

 of a parabola. These storms come from the southeast, but on 

 reacliing the latitude of our Gulf coast recurve to the northeast 

 along or off our coastline. An examination of the auxiliary chart 

 on the adjoining page shows that the air pressure in the region 

 of the storm has decreased .10 to .30 of an inch during the past 

 12 hours, and the little bars on the arrows shown on ("hart XVI, 

 from Norfolk southward, indicate that the forecast official at 

 Washington has ordered up the storm signals in anticipation 

 that the storm will move up the coast and increase in energy. 



Chart XVIII, twelve hours later, shows that his warnings were 

 timel}^ as the storm center has moved slowly northward to Jack- 

 sonville, with greatly increased energy, the l)arometer at the 

 center reading 29.1 inches, which is about .9 of an inch under 

 the normal air pressure. The auxiliary chart sliows that the air 

 pressure has decreased more rapidly during the past 12 hours 

 than during the similar period next preceding. The most potent 

 force in accelerating the motion of the eddy or hurricane was the 

 vast amount of heat energy liberated by condensation in the 

 whirling mass. 



Danger siunals have been carried northward to Norfolk, and 

 ports north of tiie storm center have been warned that the dan- 

 gerous winds will come from the northeast. I wish to make 

 plain that the storm coming from the southwest causes northeast 

 winds to flow in at its front. On the Georgia and Florida coasts 

 the signals have indicated that the wind will blow from the 

 northwest for a iaw hours, as the air whirls in behind the reced- 

 ing storm center. It will now be seen how it is possible for 

 storms to progress against the wind. 



In thilnder-storms this rule does not hold, as there is a horizon- 

 tal rolling of the atmosphere, caused by cold and heavy air from 

 above breaking through into a light and superheated stratum 

 next the earth. This rolling motion throws forward the cool air 

 in the direction in which the cloud is moving. 



Chart XX siiows a .slight aberration in the norlheast eourscof 



