CR 58:221-234 (2014)  -  DOI: https://doi.org/10.3354/cr01192

ABSTRACT: We investigated composites of sea surface temperature (SST), wind shear (WS) at 850-200 hPa, and zonal winds at 925 hPa during July-September of the hurricane season to determine interannual and decadal differences between weak (categories 1 to 3, HUR1-3) and intense (categories 4 to 5, HUR4-5) hurricanes in the main development region (MDR) of the Eastern Tropical Pacific (EPAC) during 1970-2010. SST in the MDR showed a statistically significant increase of 0.57°C over the whole period, but the frequency of HUR4-5 did not show a significant trend, while the frequency of HUR1-5 significantly decreased (-0.95% yr^-1). This trend is linked to active and inactive hurricane periods which are negatively associated with the Atlantic Multidecadal Oscillation and positively with the Pacific Decadal Oscillation (PDO). The frequency of HUR4-5 also shows a significant positive relationship with PDO and El Niño-Southern Oscillation events. This is likely due to a larger extension of the Western Hemisphere Warm Pool in the EPAC and lower WS values in the MDR during El Niño than during La Niña. Although the mean SST anomalies and WS conditions in the EPAC appear to be more favorable for cyclogenesis and intensification during El Niño, the frequency, duration, and accumulated cyclone energy of HUR4-5 are similar during El Niño and Neutral years, as are the average landfalls of category 1 to 5 hurricanes (HUR1-5). It is hypothesized that a larger size of the North Atlantic warm pool and a weaker Caribbean Low-Level Jet during Neutral years add an extra dynamical mechanism that favors cyclogenesis in the EPAC, which may not be present (or is weaker) during El Niño.

KEY WORDS: Hurricanes · Eastern Tropical Pacific · El Niño-Southern Oscillation · ENSO · Atlantic Multidecadal Oscillation · AMO · Western Hemisphere Warm Pool · WHWP · Mexico