The details of ocean waves caused by typhoons and hurricanes have been uncertain owing to the lack of precise and successive data, and difference and confusion of opinions are found with respect to the speed, travel time and direction of waves. The author tried to make the actual states clear using the data obtained by the visual observation at the ocean weather station TANGO (29°N, 135°E).
The period of high waves due to typhoons are usually 8-16 sec and remarkably longer than that of waves due to extra-tropical cyclones. They travel with the group velocity 20-45 km/hr which is not so large as believed by some people. It sometimes necessitates three days or so for conspicuous swells issued from a typhoon in the far south sea to reach Japan after the typhoon left to the west.
The direction of swell relative to the center of storm is not so simple as stated by Cline(5), Tannehill(6) and Otani(7), and the magnitude of the deviation of swells from wind, mostly to the right, depends on the path of typhoon till that time, its speed relative to the sea waves and the stage of development of the typhoon. Figs. 4-8 show the scale and direction of wind waves and swell, period and height of prevailing waves in relation to the position and direction of movement of the center during the passage of respective typhoons.
Fig. 4 represents a case when the typhoon rapidly developed, accordingly wind waves (or wind waves of swell type) prevailed with the same direction as that of wind. Figs. 5 and 6 are cases when the typhoon moved straightly with a larger speed of 50 km/hr than that of swell, and we find that in the front of the center the wind waves due to wind at that place prevailed but in the rear of the center conspicuous swells appeared with a direction different from that of wind waves. Fig. 7 shows a case when the typhoon with a small speed of travel turned the direction of movement drawing a large arc, and swells with a direction different from that of wind waves were seen in the front of the center as well as in the rear of it. An example in August of 1935 shown by Tannehill corresponds to this case. Fig. 8 is a case when the typhoon with a small speed of travel turned to the right at a somewhat steep angle, and it is easily understood that the state of sea was remarkably confused all over the ocean covered by the typhoon.
In every case, we can conclude that the waves in the rear of the center were conspicuously higher and more confused than those in the front of the center, and this is in direct opposition to Cline's opinion. Speaking of the rear segment, the wave is rather high in right quadrant than in the left quadrant. Moreover, though it was already shown by Otani(8) and Arakawa(9) that terrible pyramidal waves are likely to occur in the right rear quadrant of the storm, they may also occur in the left rear quadrant because two systems of strong waves with different directions of travel may appear and collide with each other as seen in Fig. 5
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