A new round of intense thunderstorms is spreading across southern and western Mexico on Wednesday, August 19, as Tropical Wave 29 interacts with several other atmospheric features.
Mexico’s Servicio Meteorológico Nacional (SMN) forecasts 75 to 150 mm (3 to 6 in) of rain in parts of Guerrero and Oaxaca. Totals of 50 to 75 mm (2 to 3 in) are possible across Nayarit, Jalisco, Michoacán, Guanajuato, Estado de México, Puebla and Veracruz.
The strongest thunderstorms may also produce frequent lightning, strong wind gusts and hail. SMN warns that intense rainfall could rapidly raise rivers and streams, trigger flooding in low-lying areas and increase the risk of landslides, particularly across mountainous terrain.
Why Tropical Wave 29 Is Producing So Much Rain
Tropical Wave 29 is moving westward across southern Mexico, but the wave is only one component of a much broader unstable weather pattern.
A tropical wave is essentially an elongated area of relatively low atmospheric pressure moving through the tropics. As the wave passes, it can increase low-level convergence, forcing warm and moisture-rich air upward and helping thunderstorms develop.
In this case, Tropical Wave 29 is interacting with low-pressure troughs over the Mexican interior, an upper-level cyclonic circulation and atmospheric instability. Divergence higher in the atmosphere is also helping air escape from the tops of developing thunderstorms, supporting stronger and more persistent convection.
Meteored México expects very heavy to intense thunderstorms as these ingredients overlap, with hail possible inside stronger convective cells.
Mexican Monsoon Adds Another Source of Moisture
Farther northwest, the Mexican monsoon remains active and is providing another focus for heavy rainfall.
Moisture moving inland from the Pacific and Gulf of California combines with intense summer heating and mountainous terrain to generate recurring afternoon and evening thunderstorms. This means several different weather mechanisms are simultaneously producing rainfall across Mexico rather than Tropical Wave 29 acting alone.
Disfruten de la tormenta eléctrica en ciudad #Nezahualcóyotl #lluvia pic.twitter.com/4h3WAo7IHK
— Pulserarte México (@PulserarteMx) August 19, 2026
The greatest concern in Guerrero and Oaxaca is the concentration of very heavy rainfall over steep terrain. When intense thunderstorms repeatedly affect the same watershed, runoff can quickly enter rivers and normally smaller streams.
SMN warns that rainfall may therefore cause rapid river rises, flooding and landslides, even where the most intense precipitation remains relatively localized.
The unsettled pattern is expected to continue as Tropical Wave 29 progresses westward and interacts with Mexico’s broader monsoon circulation.
