As we head into the Northern Hemisphere summer, the Southwest Monsoon is making its return to the North Indian Ocean. Once the southwesterly winds become persistent and strong, this will signal the end of the spring transition period, and the region will be entirely influenced by the Southwest Monsoon. On average, the Southwest Monsoon spans from June through September. The monsoon flow creates a convergence of moisture, promoting cloud growth and convection across the region. According to NOAA’s Climate Prediction Center, western and central India receive more than 90% of their total annual precipitation during these months.
Low pressure systems that track across the northern Bay of Bengal, Arabian Sea, and the mainland produce the majority of India’s rainfall, which is the driving force of the Indian economy. Farmers count on monsoonal rains to fill aquifers, lakes, and surrounding rivers for efficient crop growth and production. In years with insufficient rain, the nation is forced to depend on imports from other countries, creating a loss for domestic producers. Conversely, years with above-average rainfall can destroy crops and cause a poor harvest.
Droughts and floods are common across this region of the world due to variations in the strength and position of the monsoon and the interactions between the monsoon and eastward moving tropical disturbances. In the summer, heavy rainfall is expected, causing potentially devastating floods and mudslides in the higher elevations. The moist and flooded ground also becomes a breeding ground for mosquitoes, raising the threat for mosquito-born illnesses.
Recently, the Southwest Monsoon moved into the Andaman Sea and Nicobar Islands on May 14, but it has since stalled across the east-central and southeast Bay of Bengal. According to the Indian Meteorological Department (IMD), the Southwest Monsoon is expected to reach the mainland of India and set in over Kerala around May 30.
The monsoon typically sets in over Kerala on June 1, so at the present time the movement of this year’s Southwest Monsoon is near-normal. The Sri Lankan Department of Meteorology is forecasting the onset of the Southwest Monsoon across Sri Lanka this week (May 22nd-26th). This forecast was recently confirmed by NASA’s Global Precipitation Measurement (GPM) satellite instruments, which captured rainfall data from thunderstorms offshore Sri Lanka on Tuesday. NASA indicated that these instruments found rainfall rates of over 108mm (4.3 inches) and cumulonimbus extending 16 km (9.9 miles) high.