The 2013 North Indian Ocean cyclone season was an event in the annual cycle of tropical cyclone formation, in which tropical cyclones formed in the North Indian Ocean and Arabian Sea. The season had no official bounds, but cyclones typically formed between May and December, with the peak from October to November. These dates conventionally delimit the period of each year when most tropical cyclones form in the northern Indian Ocean.
The scope of this article is limited to the Indian Ocean in the Northern Hemisphere, east of the Horn of Africa and west of the Malay Peninsula. There are two main seas in the North Indian Ocean — the Arabian Sea to the west of the Indian subcontinent, abbreviated ARB by the India Meteorological Department (IMD); and the Bay of Bengal to the east, abbreviated BOB by the IMD.
The official Regional Specialized Meteorological Centre in this basin is the India Meteorological Department (IMD), while the Joint Typhoon Warning Center releases unofficial advisories. On average, 4 to 6 storms form in this basin every season.
Season summary
After a five-month break in tropical cyclone activity over the basin, the first depression of the year developed over the southern Bay of Bengal on May 10, 2013. The system subsequently developed into Cyclonic Storm Viyaru during May 12, before it made landfall near Chittagong, Bangladesh during May 16. As a result of the formation of Viyaru, the low level equatorial monsoon flow strengthened over southern parts of the North Indian Ocean, which in turn allowed the south-west monsoon to set in over the Andaman Sea and parts of the Bay of Bengal during May 17. A depression developed and made landfall on West Bengal, during May 29, before it was last noted during May 31. During June 1, the south-west monsoon set in over Kerala, the Maldives and parts of the south and central Arabian Sea. Over the next two weeks one of the fastest onsets of the monsoon over India was observed After the monsoon had set in over Kerala, one of the fastest onsets of the monsoon over India was observed, with the whole nation covered by June 16 or about a month earlier than normal. Reasons for the fast onset included a favourable phase of the Madden–Julian oscillation and the west-northwest movement of an area of low pressure between June 12–16.
Systems
Cyclonic Storm Viyaru
Originating from an area of low pressure over the southern Bay of Bengal in early May 2013, Viyaru slowly consolidated into a depression on May 10. The depression gained forward momentum and attained gale-force winds on May 11 and was designated as Cyclonic Storm Viyaru, the first named storm of the season. Operationally, the system was referred to as Mahasen; however, this was altered in 2014 with the final report and all archived advisories changed to show Viyaru. Owing to adverse atmospheric conditions, the depression struggled to maintain organized convection as it moved closer to eastern India. On May 14, the exposed circulation of Viyaru turned northeastward. The following day, conditions again allowed for the storm to intensify. Early on May 16, the cyclone attained its peak intensity with winds of and a barometric pressure of 990 mbar (hPa; ). Shortly thereafter Viyaru made landfall near Chittagong, Bangladesh. On May 17, it moved over the eastern Indian state of Nagaland.
Early in the storm's existence, it brought flooding rains to much of northwestern Indonesia, resulting in significant damage. At least four people died and six others were reported missing. In preparation for the storm, large-scale evacuations were recommended for parts of Myanmar. This resulted with people overcrowding boats to escape, and one or several vessels capsized, causing at least 39 deaths; 42 people were rescued while 19 others were unaccounted for and feared dead. The storm's expansive cloud mass also brought unsettled weather to Sri Lanka, Thailand, and southeastern India. Severe storms in India and Sri Lanka were responsible for at least 16 fatalities and significant damage; one person died in Thailand. Striking Bangladesh in a weaker state than initially expected, damage was moderate to severe. A total of 95,003 poorly constructed huts were damaged or destroyed, 17 people died, and nearly 1.3 million were affected across the country. Losses to crops exceeded ৳2.75 billion (US$35.3 million). Myanmar was spared damage and further casualties.