What Exactly is a Monsoon?

Posted: August 18, 2013, 1:43 pm by cspeciale

Parts of the Northeast have certainly experienced a very wet summer this year and some have gone as far as to describe it as a "monsoon". However, the rainfall folks along the I-95 corridor have experienced this summer is far less intense than the true monsoon thunderstorms some areas of the world rely upon each summer.

The word “monsoon” actually refers to a seasonal wind shift that creates long lasting thunderstorm and heavy rain events that add up to incredible rainfall totals. The science behind seasonal monsoon thunderstorms is similar to that of a sea breeze (see our Sea-Breeze blog for more information), but have much more dramatic impacts. First off, a monsoon typically occurs in regions where mountains or highlands exist near bodies of water that have tropical characteristics. During the summer months, the land heats up more than the water creating an area of low pressure over the land and high pressure over the water. This means winds rich in tropical moisture travel onshore. Upon encountering the mountains and highlands, the moist air is forced upwards and develops into intense thunderstorms that dump heavy yet cruical rainfall.  This pattern lasts throughout the summer supplying these countries with nearly 80% of their annual rainfall and transforms arid terrain into lush vegetation. 


If the monsoon thunderstorms are weak or even delayed, the economy of these heavily agricultural countries can suffer severely. On the other hand, strong monsoon seasons cause devastating floods that threaten life and property. Once the autumn and winter months arrive, the land becomes cooler than the water reversing the wind direction and ending the monsoon with little in the way of rainfall until the following summer. 

(Diagram from www.nc-climate.ncsu.edu/edu/k12/monsoons)

To illustrate the intensity of some of the world’s monsoon seasons, take a look at the famous Southeast Asia monsoon. During the summer, tropical moisture from the Indian Ocean streams into India towards the Himalayan Mountains and its highlands developing into continuous thunderstorms and heavy rains. On average, parts of India receive as much as 24 – 28 FEET of rain between June and September! The country is actually home to a city nicknamed the "wettest place on earth" which on average receives 463.65 inches of rain a year. For comparison, New York City averages just 49.92 inches each year. So, next time you hear someone describe our heavy rain as a "monsoon", you'll understand the intensity of a true monsoon.

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