The still night air is hot and humid. Heavy cloud obscures the stars but it is not dark. The sky is illuminated by a nearly continuous pulsing of lightning flashes, like the cameras at some red carpet event. Lightning is coming from all points of the compass, and yet none is near enough to allow me to hear the thunder.
I await the heavy deluge that never comes. This is the frustration of desert rains.
At mid-latitudes, rain follows frontal systems. It is fairly easy to predict. But here, in the Horse Latitudes, rain comes, mostly during the Summer Monsoon, in the form of random squalls and larger storms, called chubascos.
Because the monsoon is associated with heavy rain, these are often called monsoon rains. But the monsoon is not the rain. The word monsoon is of Arabic origin, meaning season. It refers to the seasonal pattern of winds found in certain regions of the world. At latitudes,between 30 and 60 degrees, the prevailing winds are from the west and are, not surprisingly, called the Westerlies. In the tropics, the prevailing winds are from the East and are called the Trade Winds. In between those two bands, lie the Horse Latitudes an area of nearly continuous high pressure, with dry, descending air. This is where the Sonoran Desert lies, and it is why you can paddle in to shore in the Gulf of California and tie your boat to a cactus.
During the summer, the air over the vast deserts of southwest North America is heated by the high sun. This hot air rises and draws air in to replace it. The Trade Winds are deflected by this pressure difference and bring warm, moisture-laden air from the tropical Pacific, along the West coast of Mexico. As this air passes overland, it is heated over bare desert and rises, becoming unstable. This unstable air creates the heavy showers and fantastic electrical storms that we call the monsoon rains.
Storms tend to follow specific paths. The chubascos of the summer monsoon tend to run up the middle of the Gulf of California, or on a parallel track a few km inland. San Carlos is located at the western edge of an east-west section of the coast, which means the storms usually pass just to the east or west of us. When a storm passes, we feel the wind, and hear the thunder but rarely get any of the precious rainfall. Our summer rain is more often associated with the tropical cyclones: hurricanes and tropical storms. A tropical cyclone hundreds of kms away will throw a wall of clouds that bring heavy rains. It also sends huge swells up the gulf to bash our shores.
This summer is a busy one for tropical cyclones. As yet they have all head out to sea, heading NW, but soon the approaching autumn will push the westerlies zone farther south, and cyclones caught in this westerly flow will be pushed ashore, bringing unwanted destruction and badly needed rain. Meanwhile we listen to the passing chubascos, and wait for the big rains that will replenish the desert, and make it bloom again.