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.

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.

[4] Operationally, the system was referred to as Mahasen;[5][nb 1] however, this was altered in 2014 with the final report and all archived advisories changed to show Viyaru.

[4][6] 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).

[14][15] 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;[16][17] one person died in Thailand.

[23] Slightly intensifying thereafter, the storm took a northward track and crossed the West Bengal coast in the evening hours of the same day, with peak winds of 45 km/h (28 mph).

Staying almost a day inland maintaining depression strength, it weakened gradually and dissipated over the states of Bihar and Jharkhand in the evening hours of May 31 due to land interaction and reduced moisture availability.

The system made landfall between Balasore, Odisha and Digha, West Bengal by the same evening at peak winds of 45 km/h (28 mph) and a minimum central pressure of 990 mbar (990 hPa).

Spending a day inland, the depression weakened, degenerating into a well-marked low-pressure area on August 1 over the state of Madhya Pradesh in India.

It gradually intensified, organizing itself into a Depression in the early hours of August 20 over coastal West Bengal and adjoining northern Odisha and Jharkhand.

Kolkata received 206 mm (8.1 in) of rainfall over a span of three days, the wettest spell of the monsoon season, causing flooding.

[31] The system's precursor low caused authorities to raise cautionary signal number 3, at all maritime ports of Bangladesh.

[33] Under the influence of an upper air cyclonic circulation, it regenerated into a low-pressure area over the Andaman Sea and adjoining Tanintharyi region.

It slowly organized itself and consolidated into a depression on October 8, followed by the Joint Typhoon Warning Center (JTWC) issuing a Tropical Cyclone Formation Alert (TCFA) the same day.

[37] Shortly before landfall, Phailin began another eyewall replacement cycle which led to slight weakening, and the system jumped back to Category 4 status.

[39] Phailin rapidly weakened as it tracked over rugged terrain, eventually dissipating into a well marked low-pressure area over the state of Bihar on October 14.

[40] The cyclone prompted India's biggest evacuation in 23 years with more than 550,000 people moving up from the coastline in Odisha and Andhra Pradesh to safer places.

[43] The JTWC issued a Tropical Cyclone Formation Alert the same day, reporting that the depression was moving into an area favorable for further intensification.

Later on November 16, the IMD issued its final advisory on Depression BOB 05, as the system weakened into a well-marked area of low pressure.

[56] Over the next several hours, the remnant low of BOB 05 moved across the central part of Southern India, and the system continued to weaken.

[58] Late on November 17, the remnant energy of Tropical Storm Podul contributed to the development of a trough over the Bay of Bengal, located near the Andaman Islands.

During the next couple of days, the storm slowly organized and consolidated, prompting the Joint Typhoon Warning Center (JTWC) to issue a Tropical Cyclone Formation Alert (TCFA) during the early hours of November 19.

[64] Helen continued to intensify into a Severe Cyclonic Storm the following day, reaching its peak intensity of 100 km/h (62 mph) with a central pressure of 990 mbar (29 inHg).

The following day, Lehar further intensified into a very severe cyclonic storm, as both IMD and JTWC reported peak winds of 140 km/h (87 mph) and a central pressure of 982 mbar (29.0 inHg).

Early on November 27, the JTWC reported the storm's low-level circulation center (LLCC) was losing its structure due to vertical wind shear, indicating a weakening trend.

[74] Four flights originating from Chennai bound to Port Blair were cancelled due to the cyclone on November 25 while 110 km/h (68 mph) winds lashed the islands.

Though the sea surface temperatures were good enough for tropical cyclogenesis, moderate vertical wind shear kept the system from strengthening too quickly.

[89] Despite the wind shear, Madi developed an eye on December 10,[90] and the JTWC assessed the system as a Category 1 equivalent for a second time.