| Summary: | Monthly precipitation records in Costa Rica are investigated to determine the possible effects of sea surface temperatures in the tropical North Atlantic and Niño 3.4 region of the Pacific during the Veranillos de San Juan (July and August). Median rainfall totals under four sets of combined sea surface temperature anomalies in the two oceanics are compared. Generally the northeast trade winds intensify during this time yielding increased rainfall on the Caribbean slope and rainshadow on the Pacific slope. El Niño events strengthen this pattern and La Niñas weaken it. The degree of response to warmer/colder waters in the Pacific is greatly modulated by sea surface temperatures in the Atlantic. The effects of a wanner Pacific are almost totally effaced when combined with a wanner Atlantic. Similarly the contrasts between the responses on either slope noted during La Niña events diminish when the Atlantic is also cooler. As sea surface temperatures of the Atlantic generally display larger time scales of oscillation (decadal) than those of the Pacific (3-7 years), their mutual interaction may explain the observed changes in the nature of the seasonal rainfall response to the El Niño-Southern Oscillation. Se analizan los posibles efectos de las temperaturas superficiales del Atlántico Norte tropical y del Pacífico, región Niño 3.4, sobre los registros mensuales de precipitación de Costa Rica durante los Veranillos de San Juan (Julio y Agosto). Las precipitaciones medias totales se comparan bajo cuatro combinaciones de anomalías de las temperaturas superficiales en ambos océanos. Los vientos alisios del noreste generalmente se intensifican durante los Veranillos, generando mayor precipitación en la vertiente Caribe y condiciones más secas a sotavento en la vertiente Pacífica. Durante El Niño, este comportamiento se refuerza, mientras que durante La Niña se debilita. El grado de respuesta a aguas más cálidas/frías en el Pacífico es fuertemente modulado por las temperaturas superficiales del Atlántico. Los efectos de ...
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