The El Niņo Southern Oscillation (ENSO) is a phenomenon that is not clearly understood.. The ability to determine ENSO cycles is extremely vital, but equally important is an understanding of its global impacts and the physics behind the ENSO occurrence. Interannual variations of ocean surface temperatures in the equatorial Pacific, has apparently had effects on weather patterns in other parts of the world. Inter-linked changes, among other phenomena, has lead to the concept of "teleconnections," that is connections between different processes occurring at locations widely- separated across the globe. During ENSO events, the normal pattern of tropical precipitation becomes disrupted, which affects tropical atmospheric circulation features, such as jet streams in the subtropics and in the temperate latitudes. One of several possible disturbances caused by ENSO is the disruption of normal hurricane occurrences in the Atlantic Basin, which includes the North Atlantic, the Caribbean Sea, and the Gulf of Mexico.
According to William Gray, the Atlantic Basin experiences more season-to-season hurricane variability than any other tropical ocean basin. There are seven factors currently being used by Gray and Landsea, to determine tropical cyclone activity, and the presence of ENSO is among one of them. It is obvious that many factors are used in the prediction of hurricanes, but when ENSO occurs, it appears that it not only tends to have an overriding effect over the other influences, but it may well alter other predictive signals. The purpose of this study is to examine connections between ENSO occurrence and hurricane activity in the Atlantic Basin. For this study, the years selected as representing the ENSO warm phase (El Niņo) were 1987 and 1997, and those selected as representing the ENSO cold phase (La Niņa) years were 1988 and 1995. Sea surface temperature anomalies (SSTAs), presented in this paper are from the month of August, which was chosen since it is one month before the peak hurricane frequency month and mid-way through the season. In this study a "normal" year, 1986, is selected and compared to cold and warm phase ENSO years.
In general, the following patterns were discovered: (a) during an El Niņo year tropical cyclone frequency was lower than the average of the last 4 decades, intensity of storms was reduced, and cyclogenesis occurred in higher latitudes, (b) during a La Niņa year tropical cyclone activity was more prolific than the average of the last 4 decades, the intensity of the storms was significantly stronger, and storm cyclogenesis occurred lower in latitude.
This study helped to establish the teleconnection that exists between the ENSO events and Atlantic Basin hurricanes, but attempting to base hurricane activity solely on the effects that ENSO has, would not be valid. Although general patterns were evident, certain aberrations were present. However, this teleconnection should be useful to forecasters for long range prediction of tropical cyclones during ENSO versus non-ENSO years.
The ability to be able to uncover accurate teleconnections between ENSO, from both oceanic and atmospheric conditions and other global events is extremely vital toan improved understanding of the coupled systems and their feedbacks on our planet. This ability, which helps to predict the hurricane season in the Atlantic Basin, will become very important in years to come to many sectors of society, if ocean temperatures continue to rise.