Weather Research CenterTMWeather Research Center Weather Museum
5104 Caroline St Houston, Texas 77004 Phone: 713-529-3076 Fax: 713-528-3538 E-mail:



The Orbital Cyclone Strike Index (OCSI) was developed in late 1985 as a tool to predict trends in tropical cyclone tracks in the North Atlantic by Jill F. Hasling and Dr. John C. Freeman of Weather Research Center. The researchers based the index on the premise that the same phenomenon or phenomena that cause the solar cycle on the sun might have a similar effect on the large scale circulation of the earth which would be reflected in the tracks of cyclones. This idea of a relationship between the sunspot cycle and cyclones is not new. Willet (1951) predicted correctly in the early 50's that the period 1959 to 1990 would have a relatively small number of hurricanes in the North Atlantic ocean. His later research found the 11 year sunspot cycle appeared to be related to the climate in the tropics. Recently Labitzke and Van Loon (1987) have showed that the solar cycle correlated highly with the general circulation depending on the phase of the quasibiennial-oscillation (QBO). The QBO is the oscillation of equatorial east-west winds which vary with a period of 26 to 30 months.

The sun has a year that varies from 10 to 13 earth years. For this research this sun year is referred to as the "sol-year" and begins with the earth year that the sunspot minimum occurs. The Sun orbits around the center of rotation of the solar system. This orbit takes 10 to 13 earth years to complete. During this orbit the sun goes through the solar cycle where the sunspots are at their minimum to the maximum and back again to the minimum. While the sun makes its orbit, the earth is orbiting around the sun and the large scale circulation patterns of the earth experience some of the same influences as the sun.

The Solar Cyclone Strike Index is made up of cycles and phases. The cycles are the sol-years and range from 10 to 13 earth years. Phase 1 of the index is each earth year when the sunspot minimum occurred and Phase 2 is each earth year one year past the minimum etc. The tracks of North Atlantic tropical storms and hurricanes where then grouped into the Solar Cyclone Strike Index (SCSI).

Each phase of the index is then summarized and landfall along the United States coastlines then compared. The highest two probabilities for each section of the coast were considered to have the highest risk of a storm strike.


1 1878S 1889 1901 1913 1923M 1933 1944 1954 1964 1976M 1986M
2 1879 1890 1902M 1914M 1924 1934 1945 1955 1965M 1977M 1987M
3 1880M 1891S 1903 1915 1925S 1935 1946 1956 1966M 1978 1988
4 1881 1892 1904 1916 1926S 1936 1947* 1957*S 1967 1979* 1989*
5 1882 1893 1905 1917*S 1927 1937* 1948 1958S 1968 1980 1990
6 1883* 1894* 1906 1918 1928* 1938 1949 1959 1969* 1981 1991M
7 1884S 1895 1907*M 1919 1929 1939M 1950 1960 1970 1982S 1992M
8 1885 1896M 1908 1920 1930 1940S 1951 1961 1971 1983S 1993
9 1886 1897M 1909 1921 1931 1941S 1952 1962 1972S 1984 1994
10 1887 1898 1910 1922 1932S 1942 1953M 1963 1973S 1985 1995
11 1888 1899S 1911S     1943M     1974    
12   1900S 1912S           1975    

The Center has been making these predictions since 1985. The current prediction is available at How accurate is OCSI? As illustrated below, OCSI predictions are more accurate than the tropical cyclone predictions made by the revered Dr. William Gray in the spring.

WRC vs. Dr. Gray vs. Actual graph

WRC vs. Dr. Gray plus-or-minus chart

Since 1900 there have only been 14 years when there were no August tropical storms or hurricanes in the Atlantic Ocean, which includes the Caribbean Sea and the Gulf of Mexico. The last year with no August storms was back in 1961. In 1961, the first storm formed on July 20 and the next storm did not form until September 2. The years with no August storm activity include: 1902, 1904, 1905, 1907, 1912, 1914, 1919, 1920, 1921, 1922, 1925, 1929, 1941 and 1961. Nine of these years were El Nino Years.

Since 1900, there have been 13 years when there was only one tropical cyclone (hurricane or tropical storm) in the North Atlantic Ocean Basin during the month of September. The last time there was only one September storm was back in 1946. The years with only one September storm were: 1902; 1904; 1911; 1912; 1914; 1919; 1922; 1925; 1929; 1930; 1938; 1939 and 1946. The two years without October or November storms were in 1914 and 1930 - both El Nino years. A strong El Nino event is probably to blame for this season's lack of tropical activity. Strong upper level westerly winds prevailed much of the season across the tropical Atlantic Ocean. These stronger winds prohibited tropical disturbances from forming.

Weather Research Center
5104 Caroline St. Houston, Texas 77004
(713) 529-3076