The eclipse track crosses one of the driest and sunniest parts of Mexico, in spite of a jumbled terrain which includes cool beaches, deserts, 3000 meter peaks and a broad 1500 meter plateau. Each of these features has an influence on the weather, but the moisture supply is so low in most areas that, with only one exception, cloud cover is sparse and sunshine plentiful. The main control on the weather is a large and permanent high pressure cell which resides in the eastern Pacific about half way between Hawaii and San Francisco. This semi-permanent anticyclone suppresses rain bearing weather systems along the California and Baja coasts, bringing the dry summers for which the area is well known.
During the winter months, weather systems arrive over the eclipse track on upper level westerly winds. During the summer, easterly low level trade winds carry the moisture which builds thunderstorms and brings the rainy season or "tiempo des aguas". May is the intermediate season, too soon for the moist easterlies, and getting very late for westerly disturbances. Still, what weather occurs on eclipse day is likely to come with the last westerly troughs moving in from the Pacific.