8 BULLETIN 354, U. S. DEPARTMENT OF AGRICULTURE. 



remarkably constant, rarely varying more than a mile from the 

 annual average of 11 miles per hour, excepting in July, when the 

 velocity rises to 13 miles, and in October and November, when it falls 

 to 8 or 9 miles. 



Hurricanes whose centers pass over the island are rare; in the past 

 40 years there have been but three, the most recent as well as the 

 most destructive being that of August 8, 1899. The recorded 

 storms of this character for the entire West Indies average about one 

 a year and occur chiefly during the months of August, September, 

 and October. 



TEMPERATURE. 



The temperature throughout the year is uniform. The records of 

 the United States Weather Bureau for a period of more than 10 years 

 show a combined average annual temperature for over 40 stations in 

 the island of 76°; during the coolest months of winter the average 

 is 73° and during the warmest months of summer 79°. The daily 

 range is much more than the seasonal range; thus at San Juan the 

 difference between the afternoon and early morning temperature is 

 10° or 11° and at an inland station may be as much as 20° or 25°. 

 In the afternoon the temperatures along the coast rise to an average 

 of 84° in the winter months and to 89° in the summer months and in 

 the early morning fall to 66° and 73°. In the hills and mountains of 

 the interior the average daily maximum is about 81° in winter and 

 87° in summer, while the corresponding minima are 61° and 68°-, 

 respectively. 



The extremes of temperature recorded during the past 10 years do 

 not differ greatly in different portions of the island. At the more 

 elevated stations the maximum range is between 90° and 95° and 

 along the coast and in the valleys 95° and 100°. The extreme maxi- 

 mum has reached 100° only three times during the 10 years, at one 

 time reaching 103°. The minimum temperatures range between 50° 

 and 55° except for stations on the immediate coast, where the tem- 

 perature seldom goes below 60°. The lowest recorded temperature 

 is 43°, and it is probable that on the highest elevations it goes some- 

 what lower. It is, however, extremely doubtful if it ever approaches 

 very near to the frost line. 



RAINFALL. 



The average annual rainfall is much more variable than the 

 temperature. The average for a 12-year period from 44 stations 

 shows 77.30 inches; for the year 1901 it was 93.72, and for 1907 but 

 64.18. The geographic distribution of rainfall shows a still wider 

 variation. The heaviest is recorded in the Sierra de Luquillo, which 

 is exposed to the full sweep of the moisture-laden trade winds. The 

 average annual rainfall here exceeds 135 inches,- with a maximum 



