After undergoing an eyewall replacement cycle, Mocha rapidly strengthened, peaking at Category 5-equivalent intensity on 14 May with winds of 270 km/h (165 mph).
Thousands of volunteers assisted citizens of Myanmar and Bangladesh in evacuating as the cyclone approached the international border.
On 2 May, the India Meteorological Department (IMD) began monitoring the potential for tropical cyclone development in the Bay of Bengal.
This potential was boosted by the approach of the active phase of the Madden–Julian oscillation, which likewise aided the formation of Cyclone Fabien in the Southern Hemisphere.
[12] The following day, both the Joint Typhoon Warning Center (JTWC) and IMD assessed the formation of a weak low-level circulation developed, which was marked as Invest 91B by the former.
[19] Located on the periphery of an established upper-level ridge, Mocha curved toward the north over the Bay of Bengal while steadily organizing.
At 12:00 UTC on 11 May, the IMD upgraded the system to a severe cyclonic storm with winds of 90 km/h (55 mph) as it developed an intense central dense overcast.
[25] While attaining this intensity, the cyclone turned north-northeastward under the influence of an anticyclonic circulation south of Myanmar and a nearby trough.
[26] High ocean heat content over the Bay of Bengal fueled a period of rapid intensification, bringing Mocha to extremely severe cyclonic storm status at 18:00 UTC on 12 May.
[1] The JTWC initially estimated 1-minute sustained winds of 260 km/h (160 mph) at 00:00 UTC of 14 May, making Mocha a Category 5-equivalent tropical cyclone.
[30] Conditions quickly became unfavorable for Mocha upon reaching areas of mid-level wind shear and with dry air beginning to intrude on the northwest side of the core.
[34] Mocha rapidly weakened from Myanmar's rugged terrain as it was downgraded to very severe cyclonic storm intensity at 15:00 UTC.
[35] The vorticity in the atmosphere, poleward outflow, and convergence would still maintain Mocha's intensity as a cyclonic storm throughout its deterioration.
[37] The depression was later marked as a low-pressure area by the IMD at 03:00 UTC, as its center was not well-defined, prompting the discontinuation of advisories on Mocha.
[38] Local authorities in Rakhine advised residents to evacuate low-lying and coastal areas in Sittwe, Pauktaw, Myebon, Maungdaw, and Buthidaung, and many were already beginning to leave as the storm approached.
[52] According to World Bank, Mocha directly caused $2.24 billion of damages in Myanmar, equivalent to 3.4% of the country's GDP in 2021.
[65] In terms of flooding, a satellite estimate released on 16 May determined at least 895 km2 (346 sq mi) of land was inundated, exposing over 141,000 people.
[67] Residents in the affected area told Reuters that up to 100 Rohingya people may have been killed, although the news agency could not verify the fatality count.
[69] UNHCR, the UN refugee agency, stated that "emergency preparations in the camps and on Bhasan Char are underway" in collaboration with the government and local humanitarian organizations.
[70] Heavy rains from the cyclone might cause landslides in Chittagong and Cox's Bazar, as well as three other hilly districts: Rangamati, Bandarban, and Khagrachhari, according to authorities in Bangladesh.
[71] A half-million people are being evacuated to safer areas in south-eastern Bangladesh ahead of a possibly catastrophic cyclone.
[74] The authorities suspended inland river transport in Bangladesh on 13 May and flight operations at Shah Amanat International Airport on 14 May.
[84] The Sri Lanka Navy (SLN) has deployed approximately 30 relief teams to assist those affected by potential floods.
[86] The state governments of Tripura, Mizoram, Nagaland, Manipur, and Assam also requested that the disaster management and all other relevant authorities take preventative measures to minimize casualties and property damage.
Due to the presence of cold air and plenty of moisture from Mocha, snow was able to accumulate, covering roads and other structures.
[94] Min Aung Hlaing, Myanmar's junta leader, visited Sittwe to assess the damage and provide donations to residents.
[95] Storm damage to communications and road infrastructure, as well as ongoing limitations imposed by Myanmar's military government, made it difficult to obtain information and send help to the affected area, according to non-governmental organizations.