Table 1. --Minimum time and fetch required for winds of various velocities to produce waves 

 of a given height and the length of the waves produced under these conditions. 

 (Calculated from Wave Report No. 73 (unpublished) of Scripps Institution of 

 Oceanography, University of California) (cont'd) 



and fetch required for winds of 20 to 60 knots to 

 generate waves of various heights. These data 

 are useful for estimating the maximum waves to 

 be expected from storms at sea. The wave length 

 was also included in the table to aid in estimating 

 the wave heights to be expected downwind from 

 storm areas. Wave length was computed from 

 the periods given in the graphs by the formula 



L = 5. 12t2 



where L is the length in feet and T is the period 

 in seconds (USNHO 1944). 



SOURCE OF DATA 



The data used in constructing the wind 

 frequency charts were supplied by the U. S. 

 Weather Bureau Records Center, Asheville, 

 N. C. , from their current files of unpublished 

 marine wind tabulations as of May 1955. The 

 data consist of tabulated individual Beaufort 

 force frequencies for each month for each 5- 

 degree square of latitude and longitude in the 

 North Pacific and adjacent seas north of 30 'N. 

 latitude. The observations cover a period of 

 more than 60 years. The total number of ob- 

 servations per square varies greatly. The 

 squares in the regular steamer lanes have as 

 many as 5, 808 observations for a single month. 



but many areas in the extreme northern portion 

 have no reports during the winter months. 



RELIABILITY OF THE DATA 



Even at the present time only about 50 per- 

 cent of the vessels plying the North Pacific are 

 equipped with an anemometer (A. J. Rohlfs, 

 USWB, personal communication) so most of the 

 wind speeds have been reported in Beaufort 

 scale estimates. For convenience in keeping 

 records, the speeds observed by vessels having 

 anemometers were also converted to the Beau- 

 fort scale. In the original scale, devised about 

 1805 by Admiral Beaufort of the British Navy, 

 the effects of wind on a ship's sails were used 

 as criteria for estimating the wind force (Byers 

 1944, p. 83). Since that time the criteria for 

 estimating Beaufort force have been adapted to 

 fit a variety of circumstances (Riesenberg 1936, 

 p. 794; Bowditch 1943, p. 52), and the wind 

 speed in knots corresponding to the various 

 forces have been determined experimentally . 

 On steam vessels the state of the sea has been 

 connmonly used for estimating wind speed. The 

 criteria for this method, approved by the Inter- 

 national Maritime Conference and in current 

 use, are given in table 2 together with the range 

 in knots and descriptive term for each force 

 (USWB 1954, p. 14). Obviously such subjective 



