Information for Yachtsmen
Panama - Pacific International Exposition San Francisco 1915

PANAMA-PACIFIC INTERNATIONAL EXPOSITION STORM FREQUENCY Compared with other portions of the United States, the San Francisco Bay section has comparatively few storms. This is be- cause most of the recognizable disturbances pass far north of this section. Except in winter very few low pressure areas move from the ocean across California, as nearly all the storms that enter the United States from the west pass far north of Central California. Since 1850 there have been during the months of June, July and August but 13 storms of the character mentioned above. During September, 14 such disturbances have been noted in the period of 63 years, and of these the most important was the storm of Sep- tember 22-26, 1904. This storm is worthy of special mention as it stands unparalleled in the history of summer and early fall disturb- ances. In 4 days 5 inches of rain fell, whereas the normal rainfall for the whole month of September is 0.30 of an inch. The relative frequency of storms increases with the advent of winter. During October there have been 40 disturbances; during November 60; and during December, January and February, about 200 per month for the total period of 63 years. Occasionally there will be a winter month without a single disturbance, as was the case in December, 1876, and February, 1864. March is a month of moderate frequency, April a month of occasional storms, and May of few storms. THE WINDS The prevailing drift of the surface air along the California coast is from west to east. The charts of wind direction issued each month for the North Pacific show in detail the relative strength and frequency of the surface winds on the California coast. Briefly, the summer winds may be grouped as follows: west to northwest, 75 per cent; north to northeast, 4 per cent; east to southeast, 3 per cent; south to southwest, 3 per cent; and calms, 15 per cent. The winter winds show a greater percentage of motion from the south. Southerly gales are not infrequent, and there is a common belief that southeast is the prevalent direction in winter months. This, however, is not true. West to northwest winds have a frequency of 30 per cent; north to northeast, 18 per cent; east to southeast, 17 per cent; south to southwest, 22 per cent; and calms, 13 per cent. It is plain from the above figures that northwest is the pre- dominant direction along the coast in the vicinity of San Francisco. Owing to the topography there are certain deflections and changes in the direction of the wind, especially through the Golden Gate from northwest to west or even west to south. During certain portions of the year, especially May and June, the northwest wind attains a remarkably high velocity. In May, 1902, and May, 1903, memorable northwest gales occurred. The fol- lowing table gives wind data as recorded at Point Reyes Light, California: 7