Interannual variability of tropical cyclone activity along the Pacific coast of North America

The interannual variability of near-coastal eastern North Pacific tropical cyclones is described using a data set of cyclone tracks constructed from U.S. and Mexican oceanic and atmospheric reports for the period 1951-2006. Near-coastal cyclone counts are enumerated monthly, allowing us to distinguish interannual variability during different phases of the May-November tropical cyclone season. In these data more tropical cyclones affect the Pacific coast in May-July, the early months of the tropical cyclone season, during La Nina years, when equatorial Pacific sea surface temperatures are anomalously cool, than during El Nino years. The difference in early season cyclone counts between La Nina and El Nino years was particularly pronounced during the mid-twentieth century epoch when cool equatorial temperatures were enhanced as described by an index of the Pacific Decadal Oscillation. Composite maps from years with high and low near-coastal cyclone counts show that the atmospheric circulation anomalies associated with cool sea surface temperatures in the eastern equatorial Pacific are consistent with preferential steering of tropical cyclones northeastward toward the west coast of Mexico.Original Abstract: Se describe la variabilidad interanual de ciclones tropicales cercanos a la costa en el Pacifico nororiental, utilizando para ello un conjunto de datos elaborado con reportes oceanicos y atmosfericos de EUA y Mexico correspondientes al periodo 1951-2006. Los ciclones cercanos a la costa se enumeran de forma mensual, lo que permite distinguir la variabilidad interanual en distintas fases de la temporada de ciclones de mayo a noviembre. De acuerdo con estos datos, el numero de ciclones tropicales que impactan la costa del Pacifico de mayo a julio (los primeros meses de la temporada de ciclones tropicales) en anos correspondientes a La Nina, cuando las temperaturas marinas superficiales en el Pacifico ecuatorial son anormalmente frias, es mayor que en anos correspondientes a El Nino. La diferencia en la cantidad de ciclones tropicales de inicio de temporada entre anos de La Nina y El Nino fue especialmente notable a mediados del siglo XX, cuando se registro un incremento de las temperaturas ecuatoriales bajas, de acuerdo con un indice de la oscilacion decenal del Pacifico. Los mapas combinados de anos con conteos bajos y altos de ciclones tropicales cercanos a la costa muestran que las anomalias de la circulation at-mosferica vinculadas con bajas temperaturas