The role of eastern North Pacific tropical storms in the rainfall climatology of western Mexico

Abstract

This paper explores the role that tropical storms (TS) of the eastern North Pacific play in the rainfall climatology of western Mexico. It uses an 18-station rainfall grid, along with a data base of storm tracks (1949 -1997). TS rainfall is defined by a distance threshold, so that for each station in the grid, daily rainfall recorded when a TS is located within 550 km of the station is considered as TS-derived; rainfall recorded in the absence of a TS or when a storm is beyond 550 km from a station is by default 'non-TS' rainfall. A variety of statistics are presented to demonstrate the static associations that exist between TS activity and regional rainfall patterns. In sum, they clearly suggest that improved seasonal forecasts of TS activity in the eastern North Pacific will be critical to advancing seasonal climate prediction for Mexico. This study also addresses the interannual variability in TS and non-TS rainfall. Principal component analysis is used to define the region's primary modes of rainfall variation. Considering the temporal behaviour of the rainfall modes, analyses reveal no statistically significant trends in TS rainfall. In contrast, non-TS rainfall modes exhibit significant trends. This study provides support for the idea that these trends are partly tied to long-period fluctuations in the ocean-atmosphere system. The results also indicate that while TS rainfall is not subject to trend behaviour, its year-to-year fluctuations, apparently, are linked to large-scale processes like El Niñ o-Southern Oscillation (ENSO) and the state of North Pacific sea-surface temperatures (SSTs). Copyright

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

“…The Niño3 index was chosen to represent ENSO variability for this study, rather than other ENSO indices based on regions farther west, because it represents equatorial Pacific SST variability directly south of the Mexican coast affected by tropical cyclones. Previous analyses of ENSO and rainfall variability (e.g., Gershunov and Barnett, 1998;Englehart and Douglas, 2001;Gutzler et al, 2002) have found a distinct change in statistics of interannual variability before and after 1977, when Pacific Ocean SSTs and the atmospheric circulation shifted in association with the PDO (Graham, 1994;Mantua et al, 1997). We therefore examine relationships between SST and tropical cyclone counts for separate periods before and after 1977.…”

“…This distance was selected based on previous research (Englehart and Douglas, 2001) showing that tropical cyclones within this distance from the coast were likely to generate observable precipitation at coastal stations.…”

“…Interannual variability of tropical cyclones may have different causes than interannual monsoon fluctuations, so attempts to understand, and predict, seasonal anomalies in summer rainfall must distinguish precipitation generated by "monsoonal" processes from precipitation produced by tropical cyclones. The fraction of total summertime rainfall along the Mexican coast attributable to near-coastal cyclones ranges from 10-20% on average (Jáuregui, 2003;Larson et al, 2005) to as much as 60% in some regions (Englehart and Douglas, 2001) or more during particular years.…”

Characterizing regional‐scale variations in monthly and seasonal surface air temperature over Mexico

“…Numerous regional-scale analyses have also been done to relate rainfall variability to changes in atmospheric circulation (e.g. Brito-Castillo et al, 2002), tropical cyclone activity (Englehart and Douglas, 2001), and the El Niño-southern oscillation (ENSO) signal (e.g. Reyes and Mejía-Trejo, 1991;Douglas and Englehart, 1998).…”

Diagnosing warm‐season rainfall variability in Mexico: a classification tree approach

“…The selected divisional locations reflect considerations of data availability -access to records from fairly consistent reporting stations over the period 1943-2006 -and the desire to sample a diverse set of climatological rainfall regimes within Mexico. The analysis purposely excludes more coastal locations where previous work indicates that tropical cyclone (TC) activity contributes significantly to warm-season rainfall regimes (Englehart and Douglas, 2001;Douglas and Englehart, 2002).…”