"The word monsoon is derived from the Arabic word mausim, which means season. Traders plying the waters off the Arabian and Indian coasts noted for centuries that dry northeast winds in the winter suddenly turn to the southwest during the summer, and bring beneficial yet torrential rains to the Asian subcontinent. We now know that these large scale wind shifts, from dry desert areas to moist tropical areas, occur in other parts of the Earth, including the Oceanic subcontinent, Southeast Asia, Australia, North America, Africa and South America."
That "North America" part? That's here. Morning comes cool and damp, with the rising sun lighting up the new flush of green that covers the basins and creeps up the sides of the mountain ranges. We do most outdoor activity in the early mornings. During monsoon, what comes up as the day wears on is the humitidy, not the heat. Unlike high summer, when afternoon temperatures routinely head for 110 degrees (F), during monsoon we rarely see 100. This last week, afternoon highs have been below 90. But the humidity! That moist flow from the Sea of Cortez sweeps over us, and with that much humidity, even temperatures in the 80s will start a thunderstorm going.
As the sun moves higher in the sky, the clouds start forming. First they come marching up the San Pedro River Valley, the Tucson valley's pipeline to the sea. They pile up on the mountain ranges -- the Santa Ritas to the south, the Rincons to the east, the Catalinas to the north. And then the sun starts working on them, adding energy to the moisture, and blowing them up into thunderstorms that come sweeping down the mountainside with a flash and a roar and a downpour of rain.
If it got hot, it cools down fast. It's not unusual to see the afternoon temperature drop from the 90s down into the low 70s in just a few minutes as the storms come through. Where it was dry, there are now raging rivers (more YouTube). The storms continue on into the night, the lightning strikes threatening fire, and power overloads. The phones go out. If you're lucky your power stays on, but anyway you can turn off the air conditioning and open up the doors and windows to let the cool damp air flow through the house so it doesn't really matter.
I go to bed early, often while it's still raining; many desert dwellers do, because we get up with the sunrise to enjoy the lovely cool mornings. And since I telecommute to NY, I'm a member of the Eastern Standard Tribe and my workday begins at 6 a.m. local. Monsoon will continue through the middle of September, off and on, sometimes stronger, sometimes weaker. We'll get half of our annual rainfall in these two+ months. And I'll be getting quick at unplugging the electronics.
If you're visiting Tucson this summer, check out the Summer Saturday Evenings at the Arizona-Sonora Desert Museum.
