El Niño / La Niña Local Effect on Tropical Systems

To examine the correlation between El Niño/La Niña events and tropical systems that affect west central and southwest Florida, we need to calculate the anomalies for the Atlantic hurricane season (May-November). Using the same El Niño/La Niña category break down as listed on the yearly anomalies page, the results were as follows:

Strong El Niño 1997 (+2.00) 1987 (+1.55) 1982 (+1.44) 1972 (+1.30) 1965 (+1.15) 2002 (+1.10) 1991 (+0.83) 1957 (+0.77)                       Weak El Niño 1969 (+0.64) 1963 (+0.64) 2004 (+0.63) 1994 (+0.62) 1986 (+0.51) 1993 (+0.50) 1951 (+0.42) 1977 (+0.41) 1953 (+0.40) 1976 (+0.34)                   Neutral 1992 (+0.24) 1990 (+0.23) 1968 (+0.23) 2005 (+0.22) 2003 (+0.22) 1979 (+0.22) 1958 (+0.22) 1980 (+0.13) 1966 (+0.06) 2001 (+0.04) 1983 (-0.03) 1960 (-0.11) 1952 (-0.13) 1981 (-0.21) 1961 (-0.21) 1959 (-0.23) 1996 (-0.24) 1967 (-0.26) 1962 (-0.29) Weak La Niña 1971 (-0.63) 1974 (-0.59) 1956 (-0.57) 1984 (-0.53) 2000 (-0.50) 1985 (-0.43) 1995 (-0.41) 1989 (-0.41) 1978 (-0.35)                     Strong La Niña 1988 (-1.58) 1955 (-1.28) 1975 (-1.17) 1973 (-1.10) 1999 (-0.98) 1964 (-0.88) 1998 (-0.87) 1950 (-0.86) 1970 (-0.84) 1954 (-0.76)

1950 represents May 1950 through November 1950, etc.

Notice that the 1997 hurricane season saw the strongest El Niño during this study. Based on these categories, a graph of the tropical systems per year for each category is linked below.

(through 2005)

There is clearly less activity during strong El Niño years than other years in this study. However, the overall relationship between El Niño/La Niña events and the tropical activity over west central and southwest Florida is not as clear cut. Even though from 1951 to 2005 a total of 16 hurricanes, 20 tropical storms, and 10 tropical depressions crossed over or near part of the area, the 55 year period of record is relatively short. While there is certainly a trend evident in the data, it would need to be done over a longer time period to be more statistically significant.

Tropical landfalls were also compared to the event of the previous winter/spring (i.e. comparing the category of El Niño/La Niña in December to April to the following hurricane season). The results are shown in the graph below.

through 2005)

Interestingly enough, there is little overall difference on whether the previous winter was a strong/weak El Niño to weak La Niña, but there is a lower occurrence following a strong La Niña.

Note: All tropical systems whose center made landfall and/or crossed our area were included in this study, along with those that had some effect on any part of west central and southwest Florida. For example, although Hurricane Wilma in October of 2005 made landfall south of our area, it was included in the study because it had some effects within our area of interest.