Climate variability on intraseasonal time scales: Severe cold and record-breaking rains in Mexico and disruptive wild fires in California in late October 2007
Lance F. Bosart, SUNY, Albany, NY; and H. M. Archambault and J. M. Cordeira
Extreme weather affected parts of Mexico in late October 2007. The passage of several unusually strong early season cold fronts in quick succession brought anomalously cold conditions to much of interior and eastern Mexico (some minimum temperatures in northern parts of the region were near 0 °C) and produced strong cold surges into the Gulf of Tehuantepec. In very late October record-breaking rains were observed in Chiapas and Tobasco states where upwards of 100 cm of rain over a two-to-three day period was reported in the mountainous areas of these states. Urban dislocation in Chiapas and Tobasco was severe in response to widespread flooding. The unusual severity of the early season cold (temperatures ~5°C below normal) in parts of central and northern Mexico and the very strong and gusty northerly winds (20-25 m s-1) along the coastal plains of Mexico adversely impacted a population accustomed to considerably less weather and climate variability at this time of the year.
The purpose of this presentation is to document how the large-scale flow variability on 10-14 day time scales produced favorable conditions for the severe cold and record-breaking rains in Mexico. In mid-to-late October an anomalously strong and eastward-displaced Pacific jet was present over the eastern North Pacific Ocean. The nose of this jet was directed toward the Pacific Northwest where heavy rains were observed. South of the jet corridor a series of surface high pressure centers crossed the Great Basin and reformed along the eastern slopes of the Rockies, resulting in strong Santa Ana conditions in southern California (where disruptive fires were reported) west of the Rockies, and cold surges east of the Rockies that extended southward across Mexico to the Gulf of Tehuantepec.
The record-breaking heavy rains in Chiapas and Tobasco occurred in conjunction with strong low-level warm-air advection that was situated along the eastward margin of the cold surge. Tropical moisture, in part from developing Tropical Cyclone (TC) Noel, reached Chiapas and Tobasco from the east. Anomalously high sea level pressure along the coastal plain of eastern Mexico in the wake of the cold surges in conjunction with steady or falling sea level pressures over the Bay of Campeche and the Yucatan Peninsula in the aforementioned warm-air advection region to the west of TC Noel resulted in the creation of exceptionally strong and moist northerly upslope flow that sustained heavy rainfall in Chiapas and Tobasco.
Session 13B, Climate and weather extremes - II
Thursday, 15 January 2009, 11:00 AM-12:00 PM, Room 129B
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