120 CLIMATIC CONDITIONS 



AVERAGE HOURLY VELOCITY OF WIND. 



(In miles per hour.) 



Hours ending. 123 456 7 89 10 11 



Morning 5.4 5.0 5.0 5.6 5.6 5.7 5.6 7.O 8.2 8.8 9.1 10.0 Noon. 



Afternoon 9.9 9.9 9.6 8.5 8.5 7.6 6.8 6.2 5.8 5.8 5.8 5.7 Mdnt. 



THUNDERSTORMS. 



The Islands are free from violent atmospheric disturbances during the 

 greater portion of the year. A comparatively mild type of thunderstorm 

 occurs in all months of the year, but they are of rare occurrence in the winter 

 months. These storms are of short duration and are frequently accompanied 

 by very heavy showers. Even in the season of greatest frequency they aver- 

 age but 4 or 5 per month. In the five years from 1898 to 1902, the average 

 annual number was 29 and the seasonal distribution as indicated by the fol- 

 lowing figures : 



AVERAGE FREQUENCY OF THUNDERSTORMS. 



Jan. Feb. Mar. Apr. May June July Aug. Sept. Oct. Nov. Dec. Year. 

 O.8 0.6 1.2 1.2 3.O 3.2 5.8 7.2 3.2 2.6 0.2 O 29 



One of the members of the Expedition was fortunate enough to secure 

 an admirable photograph of a typical thunderstorm as it appeared at sea, 

 where nothing was present to interfere with a comprehensive view of the 

 disturbance throughout its entire extent. This photograph was taken just 

 north of Abaco, and a reproduction is shown in Plate XVII, Fig. 2. 



HURRICANES. 



The Bahama Islands lie in the midst of the tracks of the West India 

 hurricanes. The line marking the mean path of these fierce tropical storms 

 passes across the eastern edge of the group during August, and along the 

 western edge during the month of September. In October the center of 

 activity again recedes eastward to its July position. The hurricane is the 

 severest type of cyclonic storm and has been dreaded by the inhabitants of 

 the Islands, and especially those sailing the seas, from time immemorial. They 

 are not of very frequent occurrence, fortunately, and they are confined prac- 

 tically to the months of August, September and October. Occasionally one 

 will appear as early as June and July, and even as early as May, but most 

 of these storms occur in August, September and October, after which there is 

 an abrupt cessation, only one storm of the kind having been recorded in 25 

 years in the month of November. 



