(03/2004)
Much of the following information is unique. You are unlikely to encounter it anywhere else, and unfortunately for those that cannot prepare for this quirk in Mexican weather they will have to learn about it the hard way.
Mexico's Isthmus of Tehuantepec (the narrow gizzard-like neck at the southern end of Mexico) is infamous for terrible Winter crosswinds ("The Tehuantepecker") that can tip over semi-trailers and 5th wheels alike. Even if a tipover is avoided, this section of Mex 200 is narrow and you don't need to deal with a semi-trailer whipping back and forth as it approaches in the opposite lane.
Thanks to the internet and any weather map of the USA displaying forecast weather fronts and high and low presure centers, you can determine if winds are a probability at "La Ventana" (the open window) or "Ventoso" (Windy!) during your projected passage.
Access a chart map of the USA (I use "wunderground.com", select and click on the subcatgory "Weather Fronts" and then wait until the updated map of the US appears.
In the Winter, a high pressure center, that is centered over the state of Texas is highly likely to cause sharp northerly winds across the Isthmus. You can either "wait it out" in say the city of Tehuantepec or Tuxtla Gutierrez, or make a dash for it, right at the crack of dawn. It takes about an hour and a half for a slower RV rig to clear this area (as a worst case) and you need to be clear of it before the sun has been up two hours.
Note as you pass through this area how the wind has sculpted trees, shrubbery, telephone poles and highway signs to all point to the south (right-angle across the highway. There is very seldom no wind here.
Regardless of how lucky you may feel about timing your crossing, you have better check the retention and security of fastening of all of your awnings, before you cross. Salty travelers use plastic cable ties to solidly bind awning hardware. Stow loose paperwork floating about the cockpit or cab. I've seen a fierce gust suck maps, receipts and notes out a partially cracked-open wing window.
Saludos de San Cristobal de Las Casas, Chiapas