584 



Principles of Weather Forecasting. 



corded by the Weather Bureau, moved along axes within 

 the northern belt marked a axis of low areas." 



It is clear that so long as such conditions as these pre- 

 vail but little rain could fall in the United States, and all 

 the northern portion must have unusually warm weather. 

 The weather must be clear and dry because along the axis 

 of high pressure the air is descending from the higher al- 

 titudes where it is already dry, and in descending must 

 become still dryer because of increasing temperature due 

 to compression. As this is the air which must be drawn 

 toward the low areas on either side of the axis it could con- 

 tribute but little moisture for rainfall in either system of 

 lows, and the map shows that but little fell. 



FIG. 271. Path of the West Indian Hurricane of Sept. 1-11, 1900. 



So long as a high pressure occupies the Gulf and At- 

 lantic states, this effectually shuts off the moist gulf and 

 ocean air and forces the storm centers to maintain a high 

 northerly course. Then, too, as long as storms pursue a 



