FORECASTING OCEAN WAVES’ 
By W. H. MUNK and R. S. ARTHUR 
University of California, Scripps Institution of Oceanography 
Introduction 
One result of the interaction of wind and ocean is the 
generation of surface waves. Prior to 1940 a few inade- 
quate empirical rules formed the only basis for the 
prediction of wind-induced waves. A concentrated effort 
under the stimulus of wartime demands has resulted in 
the development of relationships which make possible 
the forecasting of ocean waves from synoptic meteoro- 
logical data. 
As an introductory example, reference is made to the 
meteorological situation north of the Hawanan Islands 
in early January 1947. An intense low-pressure center 
remained virtually stationary 1000 miles to the north- 
east of the islands for a period of more than 72 hours 
(Fig. 1). On January 1 and 2, the winds in an area ex- 
JANUARY 1, 1947 
1330 HST 
160° 
Fig. 1.—Weather map for 1330 Hawaiian Standard Time, Janu- 
ary 1, 1947. The shaded area represents the fetch. 
tending from 500 to 1200 miles north of the islands 
were force 8-10 and direction N-NNW for a period of 
36 hours. This area comprised the fetch and computa- 
tions based on wind velocity, duration, and the fore- 
casting relationships give a wave height of 38 ft and a 
period of 11.3 sec at the southern boundary [1]. The 
1. Contribution from the Scripps Institution of Oceanog- 
raphy, New Series No. 511. Many of the results discussed 
here are based on research supported by the Office of Naval 
Research, Navy Department, under contract with the Uni- 
versity of California. 
characteristics of the wind waves which are in the 
process of generation in such a fetch are referred to as 
state of sea or simply sea. After the wind waves left 
this particular area of direct influence of intense winds, 
they continued onward as swell through a region of 
relatively weak winds, and reached Hawaii in 28 hours 
after having traveled a distance of 600 nautical miles. 
Over this decay distance the height of the significant 
waves decreased and the period and length increased. 
Computations yield a swell of height 22 ft and period 
14 sec, and available observations compare favorably 
with these calculations. Further computations show the 
swell reaching Palmyra Atoll, which is 900 miles south 
of Hawaii, with a height of 12.5 ft and a period 17 sec 
after an additional travel time of 29 hours. 
The damage in Hawaii was estimated at between one 
and two million dollars. Three waves are reported to 
have inundated low-lying Cooper Island in the Palmyra 
group. Although these wave conditions are extreme for 
Hawaii and Palmyra, wave damage in general is by no 
means rare. Damaging waves may even move from one 
hemisphere to another. In April 1930, more than 20,000 
tons of superstructure stone were displaced from the 
Long Beach, California, breakwater by the action of 
swell which in all probability had its origm in the 
“Roaring Forties” of the South Pacific Ocean. The 
‘Tollers” of St. Helena and Ascension, which cross the 
equator after moving from the North Atlantic, have 
been famous since at least 1846, when thirteen vessels 
were driven from their moorings and wrecked on the 
shores of St. Helena. Reports of the disaster mdicate 
that waves broke seaward of the vessels at a depth of 
around 20 m which denotes that breaker height was 
approximately 50 ft. 
The primary motivation for the development of a 
wave-forecasting method has been the fact that waves 
are a nuisance. This problem came into particular 
prominence during the planning in 1942 of the invasion 
of North Africa. In that year, Instructor Commander 
C. T. Suthons, R. N., began an investigation of wave- 
forecasting techniques in England, and the same prob- 
lem was studied in the Oceanographic Section, Direc- 
torate of Weather, Headquarters, Army Air Forces. 
The study was continued at Scripps Institution of 
Oceanography under Air Force and, later, Navy sup- 
port, and in 1943 the method which was used through- 
out the war had in essence been developed [8]. Although 
oceanographers played an important role in the de- 
velopment of forecasting methods, the application is 
best carried out by meteorologists. 
Since waves represent the effect of the wind inte- 
grated over time and distance, forecasts of waves can 
be made from a knowledge of only the large-scale fea- 
tures of the wind distribution. Such forecasts are likely 
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