The 2013 North Indian Ocean cyclone season is an ongoing event in the annual cycle of tropical cyclone formation. The North Indian Ocean cyclone season has no official bounds, but cyclones tend to form between April and December, with the peak from May 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.
Originating from an area of low pressure over the southern Bay of Bengal in early May 2013, Mahasen 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 Mahasen, the first named storm of the season. 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 Mahasen 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 85 km/h (50 mph) and a barometric pressure of 988 mbar (hPa; 29.18 inHg). Shortly thereafter Mahasen 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 ৳400 million (US$5.14 million). Myanmar was spared damage and further casualties.
Within this basin, a tropical cyclone is assigned a name when it is judged to have reached Cyclonic Storm intensity with winds of 65 km/h (40 mph). The names were selected by members of the ESCAP/WMO panel on Tropical Cyclones between 2000 and May 2004, before the Regional Specialized Meteorological Center in New Delhi started to assign names in September 2004. There is no retirement of tropical cyclone names in this basin as the list of names is only scheduled to be used once before a new list of names is drawn up. Should a named tropical cyclone move into the basin, from the Western Pacific then it will retain its original name. The next six available names from the list of North Indian Ocean storm names are below.
This is a table of all storms in the 2013 North Indian Ocean cyclone season. It mentions all of the season's storms and their names, durations, peak intensities (according to the IMD storm scale), landfall(s) – denoted by bold location names – damages, and death totals. Damage and death totals include the damage and deaths caused when that storm was a precursor wave or extratropical low, and all of the damage figures are in 2013 USD.