It’s night, about an hour after sunset. The fluffy clouds of the afternoon have congealed into a solid mass of blackness, blocking out the stars. Yet all is not dark. There are flashes beyond the hills, several every second, coming more frequently as the minutes pass.
While the sun was up the humidity was quite bearable. Now that the sun has set, the air has become so saturated that the sweat glistens on my skin and soaks my clothes, refusing to evaporate. This is the summer monsoon.
When we hear the word “monsoon” we may think of a tropical forest, of swollen, muddy rivers, of flooded roads, of hot, humid nights alive with the buzzing of insects and the drumming of rain on tin roofs. In some parts of the world, that is a pretty accurate picture. But, despite what many people from the American Southwest are led to believe, monsoon is not rain. You hear up in Tucson, “We had a real monsoon last night, I’ll tell ya.” They get that from the phrase “monsoon rain”. The fact the word “rain” is in the phrase should tell you that monsoon is not a type of rain. You don’t hear people talk of “thunderstorm rain” or “heavy shower rain”; that would be redundant.
So what is monsoon then? The word comes from the Arabic, mawsim, meaning “season”. The monsoon is a seasonal wind-driven weather pattern, which brings dry weather during the winter, and wet weather in the summer. The Indian sub-continent and SE Asia all the way to N Australia are all affected by this weather pattern, as is West Africa and the W coasts of the Americas.
This seasonal shift is what gives it the name monsoon, but the wind pattern is nothing more than a sea breeze on a very large scale. Here in Sonora, the desert heats up in the summer faster than the water from the Gulf of California. The hot, desert air rises, leaving low pressure behind, which is filled in by the cooler air from the sea. As this cooler (not exactly cold), humid air moves inland it is pushed upward over local mountain ranges. As the air rises, two things happen. The air becomes over-saturated with moisture and forms tall clouds with growing tops. And the ascending clouds generate static electricity. This build-up becomes too much for the cloud, and a thunderstorm is the result.
Even the hardiest desert shrub needs rain. All through the winter and spring the desert has become drier and drier. The hill-sides are rock and gravel, with a sparse cover of bunches of sere, grey twigs, and the occasional cactus.standing in green defiance. The arrival of the monsoon has been a cruel joke to this tough vegetation. Hot humid air gives no relief and the nightly show of distant lightning does nothing to quench a desperate thirst.
As the monsoon progresses, the storms have grown in size and approached a little closer every night. Some nights they are close enough to hear the thunder (typically less than about 11 miles or about 18 km), and we may even get a spatter of raindrops that glue the dust to the windshield on my pickup without being quite enough to join together and wash the dust away. So we wait. It will come eventually. It must.
And it finally does. Lightning blindly stabs the ground with its crooked spear, shaking the heavens and the earth with great booms of thunder that roll around the hills, blending one with the next in a continuous rumble like the march of an army of giants. The still, moist air is suddenly pushed aside by a strong breeze and you can hear the rain approach. It comes as a wall, pouring from the sky in a solid mass of water, momentarily almost drowning out the sound of thunder.
Soon both thunder and rain abate slightly, and during the flashes of light, one can see that the road has been turned into a creek, the middle washing away down the street, leaving a deep, stony gash where a dirt road used to be. Nothing can be done about it, so we watch the storm and celebrate.