October 1999 Mexico Floods - Meteorological History

Meteorological History

Beginning around September 10, heavy rainfall occurred sporadically in southern Mexico and into Central America, influenced by a broader storm system related to Hurricane Floyd. Toward the end of September, heavy rainfall occurred in the mountains of northeastern Mexico, which prompted officials to open flood gates. The rains occurred throughout Mexico for about two weeks before the worst of the precipitation began, and saturated soils before the heaviest rainfall in October.

On October 4, Tropical Depression Eleven developed in the Bay of Campeche about 145 mi (233 km) northeast of Veracruz, having originated from a tropical wave. Due to weak steering currents, the depression moved erratically, initially to the south and later to the west-northwest. It failed to intensify due to a surface trough over the central and eastern Gulf of Mexico, connected to a cold front. While the depression was drifting, it produced large areas of convection over eastern Mexico, aided by high humidity from the gulf and from the Pacific Ocean. On October 6, the circulation was absorbed into the trough, although rainfall continued to occur through October 9. A week later, Hurricane Irene affected southern Mexico with strong rains. Additional rainfall occurred on October 18 in Tabasco, causing further flooding; the waters in the state began receding on October 28. The wet conditions in eastern Mexico, occurring at the same time as hot, dry conditions elsewhere in the country, were possibly related to La Niña conditions.

Due to easterly wind shear and the convection along the storm's western periphery, the tropical depression dropped heavy rainfall in the states of Puebla, Tabasco, Hidalgo, and Veracruz, peaking at 43.23 in (1,098 mm) in Jalacingo, Veracruz. This was the highest rainfall total in Veracruz from 1981 to 2010; statewide record peaks were also reported in Puebla and Hidalgo. The depression was the third wettest tropical cyclone in Mexico from 1983 to 2006, after Hurricane Wilma in 2005 and Tropical Storm Frances in 1998. The heaviest of the rainfall occurred along the Sierra Madre Oriental, which is a mountain range in eastern Mexico and the source for several regionally important rivers. Tuxpan, Veracruz recorded 6.2 in (157.7 mm) in a 24 hour period on October 4, which was greater than the average October rainfall there and was about one-ninth of the annual total. A station in Hidalgo reported 4.02 in (102 mm) on October 4, which was also greater than the average October rainfall and was about one-eighth of the annual total. The return period was estimated as high as a 1 in 67 year event at Xicotepec, Puebla, and it was estimated that such floods in Mexico occur only twice per century; similar floods occurred in September 1944 in the same region, although the area was less populated then.