Monsoon Rain is Falling in the Sahara

The Atlantic hurricane season this year has so far been rather anemic. The article at the link blames warm waters in the North Atlantic for the situation. The warm waters have shifted the annual monsoon season in Africa farther north. They are receiving rain throughout the Sahara Desert, which happens only rarely. So, the proto-hurricanes that spin off westward from the African coast are passing offshore too far north, and not encountering the warm waters that would get them going.

In normal years the subtropical high pressure area, a heat dome, sits relentlessly over the Sahara. The sands are so reflective, the air so dry and the ground is so hot that heat is actually lost to space over the Sahara under normal conditions. That leads to hot days and cool nights with huge temperature swings especially near the equinoxes. This September’s equinox period will be very abnormal with cooler days, warmer nights and intrusions of tropical air from the African monsoon.

The Sahara wasn’t always a desert. From the beginning of the interglacial period up to 6000 years ago, there were lakes in the Sahara. Megalake Chad and the other Saharan lakes were so large that they kept the climate moist even after the orbital parameters that brought maximum insolation to the Arctic in late spring and early summer ending the last glacial period became less favorable. However, 6000 years ago the solar heating patterns caused by earth’s orbital variations brought more ocean warming to the southern hemisphere and less to the northern hemisphere and the north Atlantic cooled. The cooling of the north Atlantic waters brought on the drying of the Sahara and the desert conditions that have predominated the region for the past 5000 years.

But this summer something is different. The waters of the north Atlantic are relatively hot while the waters of the south Atlantic are relatively cool. And the waters of the Indian ocean on the east coast of Africa are very warm. And the Mediterranean sea is hot. 

The high heat content of the north Atlantic and the Mediterranean sea has affected the atmospheric circulation patterns bringing exceptional heat to far northern Europe and allowing the heat dome over western north Africa to break down, bringing monsoon moisture north into the Sahara desert.