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.

Owing to adverse atmospheric conditions, the depression struggled to maintain organized convection as it moved closer to eastern India.

Early on May 16, the cyclone attained its peak intensity with winds of 85 km/h (55 mph) and a barometric pressure of 990 mbar (hPa; 29.23 inHg).

Early in the storm's existence, it brought flooding rains to much of northwestern Indonesia, resulting in significant damage.

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, the storm caused moderate to severe damage.

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.

[1][2] The India Meteorological Department later renamed the system as Viyaru in their final reports and removed Mahasen from all previous archived advisories.

With conditions favoring intensification, low wind shear, excellent poleward outflow, and unusually high sea surface temperatures (estimated at 31 °C (88 °F)), the system was anticipated to become a tropical cyclone over the following days.

[5] A pulse in the Madden–Julian oscillation, coupled with a convective Kelvin wave allowed the system, along with its Southern Hemisphere counterpart Tropical Storm Jamala, to further develop.

[6] Following additional organization, the Joint Typhoon Warning Center (JTWC) issued a Tropical Cyclone Formation Alert for the low on May 10.

In light of this data, the JTWC classified the system as Tropical Cyclone 01B while it was situated roughly 1,950 km (1,210 mi) south of Chittagong, Bangladesh.

At the time, the agency anticipated significant strengthening of the cyclone, forecasting it to attain winds in excess of 155 km/h (95 mph).

[15] Dry air soon began to flow into the circulation, disrupting convection and causing the low to relocate eastward and become partially exposed.

[17] On May 13, steering currents weakened around the cyclone due to a shortwave trough over India, causing Viyaru to slowly move northwestward.

[21] Early on May 16, the system attained its peak intensity with a barometric pressure estimated at 990 mbar (hPa; 29.23 inHg).

[24] The system further degraded as it moved over mountainous terrain and was last noted as a well-marked area of low pressure over Nagaland on May 17.

One person died in Simeulue Regency after being struck by a fallen tree and another went missing offshore when his motorboat sank.

Near the border of Aceh and North Sumatra, a landslide struck a bus with eight people in it and sent it into the nearby Laekombi Lake.

[32][33] Farther west, severe storms in Andhra Pradesh, India caused eight deaths and injured four others; all of the casualties were the result of lightning.

[34] The system also brought a hot airmass to parts of southeastern India, with Chennai recording temperatures as high as 39.6 °C (103.3 °F).

[35] On May 13, coastal districts of Odisha were placed on alert for heavy rains and gusty winds associated with the passage of the cyclone.

Storms associated with the cyclone also caused significant damage in Nakhon Sawan Province, resulting in one death.

[43] Though the storm was weaker than anticipated, rains over the country preceding the cyclone led to concerns of widespread flooding.

[58] Off the coast of Rakhine State, a large boat was towing two smaller ones to a safer area, late on May 13, when one or more of them capsized after striking rocks.

With the majority of evacuees being internally displaced persons, many were hesitant to listen to orders from the military, and some refused to leave their temporary shelters.

[66] Had the storm maintained a more easterly track, officials believed that the Rohingyan people's refusal to evacuate would have resulted in many deaths.