North Indian ocean tropical cyclones
During the Indian Summer Monsoon, a low level jet covers the Arabian Sea. This causes vertical wind shear to increase over the Arabian Sea and inhibits cyclogenesis in the region. Hence, less tropical cyclone activity compared to the Bay of Bengal.

http://www.meted.ucar.edu/tropical/textbook_2nd_edition/print_3.htm#page_5.3.0
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http://www.nature.com/nature/journal/v479/n7371/full/nature10552.html#ref1
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