COMPARISON OF DEEP WATER WAVE FORECASTS BY THE 
DARBYSHIRE AND BRETSCHNEIDER METHODS AND RECORDED 
WAVES FOR POINT ARGUELLO, CALIFORNIA, 26-29 OCTOBER 1950%* 
There are today essentially two published methods of making wave fore- 
casts. The first is a several times revised version of the Sverdrup-Munk 
method originally published in the early days of World War II (1)**, the 
latest revisions being incorporated in a report by Bretschneider(2). The 
other is an outgrowth of British work during the war. It is given in its 
most advanced state in a recent article by Darbyshire(3). 4 short comparison 
of the waves recorded during a single storm and those forecast by the two 
methods is believed to be of interest. 
A rather extensive forecast by the Bretschneider method had already been 
made for the storm of 26-29 October for Point Arguello, California(l,5), and 
an analysis of the waves reaching Point Arguello was available from the 
University of California pressure recorder situated in a depth of about 80 
feet off Point Arguello. The conditions of this storm during a portion of 
which surface winds in excess of O knots were observed were thought to be 
relatively representative of the winter lows approaching the California 
coast. This storm was, therefore, chosen for the comparison. 
The results of the comparison are shown in Figure 1. Figure la shows 
a comparison of the significant heights and periods as obtained by the two 
methods with those observed. It will be noted that the Bretschneider fore- 
cast results in two wave trains after 0500 on the 28th; therefore a dashed 
line has been added representing the heights obtained if these two trains 
are combined by the square root of the sum of the squares; this latter should 
be more nearly what would be obtained from the recorder. From Figure la it 
is seen that the major disparity between the methods is one of time. Figure 
1b has been plotted to show this more fully. In this figure the time bases 
of both the Bretschneider and Darbyshire forecasts have been shifted to 
make the time of the peaks correspond with that of the recorded peak; this 
required a 2-hour retardation (shift to the right on the time base) for the 
Bretschneider forecast, and a 16-hour advance (shift to the left) for the 
Darbyshire forecast. When this time shift has been made, it is readily 
seen (Figure 1b) that both methods of forecasting give the same general 
curve of wave height, with the Darbyshire method following the observed 
curve somewhat more closely except for a 2.5-foot error at the storm peak. 
Both methods give values of the same order of magnitude and, statistically, 
* The analysis by the Darbyshire method was made by Mortimer Datz, who also 
prepared the initial draft of this report. Mr. Datz has since left the 
staff of the Board te finish his studies abroad, and this final draft of 
his report has been prepared by the Research Division. 
#* Numbers in parenthesis refer to the bibliography at the end of the article. 
