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Cyclone Mocha

North Indian Ocean cyclone in 2023

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Through Indian Ocean, Bangladesh and ASEAN

Thousands of volunteers assisted citizens of Myanmar and Bangladesh in evacuating as the cyclone approached the international border. Evacuations were also ordered for low-lying areas in Sittwe, Pauktaw, Myebon, Maungdaw, and Buthidaung. In Bangladesh, over 500,000 individuals were ordered to be relocated from coastal areas of the country due to the storm's approach. Officials from the military declared the state of Rakhine a natural disaster area. Several villages in Rakhine State were also damaged by the cyclone. The death toll for Cyclone Mocha varies significantly. ASEAN reported a total of 145 deaths, whereas the National Unity Government of Myanmar (NUG) stated that Cyclone Mocha killed at least 463 people, including three indirect deaths in Bangladesh. The storm also injured 719 people and left 101 others missing. It caused about US$2.24 billion of damage in Myanmar.

Elsewhere, thousands of homes were destroyed in Bangladesh. Twelve people were injured, and the agricultural damage there reached ৳115 million (US$1.07 million), though impact was less severe than initially feared. Seven people in Sri Lanka were indirectly injured and another seven were reported missing due to the cyclone. In India, 5,749 people across over 50 villages were affected, and at least 236 houses were damaged. The remnants of Mocha then contributed to blizzards in China.

Meteorological history

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. By 7 May, converging winds were becoming increasingly conducive for the development of a low-pressure area. 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. On 9 May, the IMD upgraded the system to a depression as very intense atmospheric convection consolidated near the center. The JTWC issued a Tropical Cyclone Formation Alert on the system. On 10 May, the IMD upgraded the depression to a deep depression, and subsequently to a cyclonic storm on 11 May. It received the name Mocha. As fragmented rainbands wrapped into the center and thunderstorms continued to burst over the center, the JTWC followed suit in upgrading the system to Tropical Cyclone 01B.

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. With time, a ragged eye structure formed and occasionally appeared on satellite imagery. On 12 May, Mocha became a very severe cyclonic storm as an elongated eye became more readily defined. Around this time, Mocha reached 1-minute sustained winds of 165 km/h (105 mph) according to the JTWC, equivalent to Category 2 strength on the Saffir–Simpson hurricane wind scale (SSHWS). While attaining this intensity, the cyclone turned north-northeastward under the influence of an anticyclonic circulation south of Myanmar and a nearby trough. 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. However, this phase was soon interrupted by the onset of an eyewall replacement cycle.

After completing its cycle on 13 May, the eyewall became well-defined, resulting in another period of rapid intensification. Low vertical wind shear and robust outflow facilitated the strengthening, and Mocha reached 1-minute sustained winds of 240 km/h (150 mph), equivalent to Category 4 strength on the SSHWS. Mocha achieved its peak intensity at 18:00 UTC, when the IMD estimated winds of 215 km/h (130 mph), just under super cyclonic storm intensity. Its barometric pressure was assessed at 938 hPa (27.70 inHg). The JTWC initially estimated 1-minute sustained winds of 280 km/h (175 mph) at 00:00 UTC of 14 May, making Mocha a Category 5-equivalent tropical cyclone. However, the agency subsequently revised the estimate to 270 km/h (170 mph).

Mocha was a large storm and had a symmetrical eye about 37 km (20 nmi) wide. 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. The eye rapidly eroded as the cloud tops became significantly warmer. Mocha made landfall at 07:00 UTC just north of Sittwe, Myanmar, with 3-minute sustained winds of 215 km/h (135 mph). The JTWC issued its final bulletin on the storm upon landfall and estimated 1-minute sustained winds of 195 km/h (120 mph). Mocha rapidly weakened from Myanmar's rugged terrain as it was downgraded to very severe cyclonic storm intensity at 15:00 UTC. Wind shear also increased and contributed to the weakening. The vorticity in the atmosphere, poleward outflow, and convergence would still maintain Mocha's intensity as a cyclonic storm throughout its deterioration. On 15 May, Mocha weakened into a depression at 00:00 UTC as it tracked east-northeastward. 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.

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