Precipitation Variability over the Caribbean and Tropical Americas Associated with the Southern Oscillation

Seasonal and annual (July through June) precipitation data for up to 197 stations are used to analyze variability in the High/Dry (H/D) and Low/Wet (L/W or warm event) modes of the Southern Oscillation (SO) over the tropical Americas and the Caribbean Islands to 30°S latitude. Precipitation is significantly higher during H/D events than during L/W in northern summer, autumn and winter at most stations in the southern Caribbean and northern South America including the northern Andes and Amazon River basin. Precipitation is, in general, significantly higher in L/W than in H/D modes at higher subtropical latitudes of both hemispheres, especially in northern autumn and winter over the southern United States, Cuba and Mexico, and in spring and autumn over southern Brazil, Paraguay and Argentina. A similar pattern of spatial precipitation variability occurs in the July–June data and significant H/D minus L/W precipitation differences are found at one-third of the stations. Although drought occurs in Northeast Brazil in some L/W years such as 1982–83, rainfall in other L/W events is above normal, and overall the role of the SO in precipitation variability is not as apparent in Northeast Brazil as it is in northern South America and the Caribbean.