From the equator, Pacific winds travel northeast across Mexico, whereas Atlantic or Gulf winds blow north or in the opposite and prevaling direction. Prevailing winds in Mexico are off the Gulf travelling west to reach the altiplane by 2,000 m. This, in most years, means less rain and mosquitoes going west from Tamaulipas (800-1000 m/yr) to Durango (200-300 m/yr). Changing rainfall patterns have acute effects due to the usual 7-month annual droughts. Convection currents bring light rain in May, ending the drought. Cyclonic winds occur mainly in July and August into September. Humidity is higher for Pacific winds than Atlantic ones. Climate is not to be treated as regular any more than the data are easily retrieved, even though weather station work is very good. All such information is needed for vector control.