North Indian Ocean cyclone in 2023
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Extremely Severe Cyclonic Storm Mocha () was a powerful and deadly tropical cyclone in the North Indian Ocean which affected Myanmar and parts of Bangladesh in May 2023. The second depression and the first cyclonic storm of the 2023 North Indian Ocean cyclone season, Mocha originated from a low-pressure area that was first noted by the India Meteorological Department (IMD) on 8 May. After consolidating into a depression, the storm tracked slowly north-northwestward over the Bay of Bengal, and reached extremely severe cyclonic storm intensity. 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). Mocha slightly weakened before making landfall, and its conditions quickly became unfavorable. Mocha rapidly weakened once inland and dissipated shortly thereafter.
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 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 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 , equivalent to Category 4 strength on the SSHWS. Mocha achieved its peak intensity at 18:00 UTC, when the IMD estimated winds of , just under super cyclonic storm intensity. Its barometric pressure was assessed at . The JTWC initially estimated 1-minute sustained winds of at 00:00 UTC of 14 May, making Mocha a Category 5-equivalent tropical cyclone. However, the agency subsequently revised the estimate to .
Mocha was a large storm and had a symmetrical eye about 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 . The JTWC issued its final bulletin on the storm upon landfall and estimated 1-minute sustained winds of . 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.
Effects.
Myanmar.
Preparations.
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. Communities and aid agencies in Myanmar were preparing for Cyclone Mocha's arrival. The Myanmar Red Cross Society prepared for a major emergency response with the support of the International Federation of Red Cross and Red Crescent Societies (IFRC). More than 78,250 people evacuated from at-risk areas, including 18,800 internally displaced persons in Rakhine. The nation's government preparations for shelter stockpiled to accommodate 100,000 people. Roughly 4,000 people evacuated from Sittwe while 20,000 other residents sought refuge in local shelters.
Large-scale search and rescue teams were placed on standby, consisting of 3,207 personnel equipped with 1,009 land and 242 water vehicles. Dozens of medical personnel and rapid response teams were deployed to Rakhine and Chin. Non-food items for more than 10,000 people were readied. According to ASEAN, Myanmar's government was better-equipped to handle disasters since Cyclone Nargis in 2008. The World Food Programme (WFP) in Myanmar said it was preparing food and relief supplies to support over 400,000 people in Rakhine and nearby areas. According to the United Nations Office for the Coordination of Humanitarian Affairs (OCHA), Mocha was anticipated to reach Myanmar's Rakhine state and northwest region, where six million people require humanitarian assistance and 1.2 million are displaced. The World Health Organization has positioned 500,000 water purification pills in Myanmar, along with additional supplies. The ASEAN Coordinating Centre for Humanitarian Assistance (AHA Centre) warned of the possibility of a "catastrophic disaster" and stated that it was coordinating with Myanmar's military to fly essential supplies from warehouses in Thailand and Malaysia. State TV reported that the military government was prepared to send food, medicine, and medical personnel.
Impact.
According to media reports, at least 460 people were killed and hundreds of others were left missing, most of them Rohingya refugees. State media and local officials said at least 145 people died across the country. Over 700 people were also injured. As of 18 May, at least 183,042 houses, 1,770 religious buildings, 1,397 schools, 227 medical facilities, 2 airports and 340 government buildings were destroyed across the country. 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.
The majority of the deaths occurred in Rakhine state. One woman also died in the Salin Creek on 14 May. Several villages from Sittwe, Mrauk-U, Kyauktaw and Minbya Townships of the state were demolished. In Kyawtaw, nearly 90 percent of houses in the town were destroyed. At least 10 villages in Salin Township were flooded due to increased water level of Salin Creek by heavy rains. On Munaung Island, two women died and 1,000 houses were destroyed, including 400 in Pyaeng Taung village. In Chin State, at least 1,136 houses were destroyed in seven townships. Two people were killed by a landslide near Tachilek. A storm surge estimated at impacted coastal communities in Rakhine. Parts of Sittwe were flooded by the surge, leaving streets and homes submerged. Severe winds knocked down a communication tower in Sittwe. Roofs were blown off houses, and billboards flew off buildings in Yangon. 
After the cyclone made landfall, communication networks in Rakhine were damaged, according to the UN and local media. The towns of Chauk and Sinphyukyun reported record rainfall totals of and respectively, each well above their previous record totals slightly below . Officials from the United League of Arakan estimated the damage in Rakhine state were at US$1.5 billion. In terms of flooding, a satellite estimate released on 16 May determined at least of land was inundated, exposing over 141,000 people. This was in a survey of around . Following Cyclone Mocha's arrival, up to 16 million people (5.6 million being children) were potentially exposed to the storm's affects, including 1.2 million displaced.
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. News site Myanmar Now said hundreds were missing and "feared dead". The UN High Commissioner for Refugees said refugees died from drowning at camps and additional people were missing.
Bangladesh.
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. 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. A half-million people are being evacuated to safer areas in south-eastern Bangladesh ahead of a possibly catastrophic cyclone. The WHO deployed 40 ambulances and 33 mobile medical teams in Cox's Bazar. In addition, Arjun Jain, the UN's principal coordinator for the Rohingya refugee response in Bangladesh, says that there are numerous ambulances and mobile health teams available to support Bangladeshis in need as well as refugees. These teams are highly trained to assist the elderly, children, and the disabled.
The authorities suspended inland river transport in Bangladesh on 13 May and flight operations at Shah Amanat International Airport on 14 May. The Bangladesh government launched a large evacuation campaign to relocate almost 500,000 residents along the country's southern coastlines. By 14 May, approximately 1.27 million people evacuated from Cox's Bazar and over 100,000 from Chittagong.
At least 2,522 houses in Cox's Bazar were destroyed, with another 10,469 others damaged. On St. Martin's Island, 700 houses were destroyed and at least 12 people were injured including one in critical condition. The cyclone impact were less than initially feared as the storm surge was less than anticipated. 500 houses were destroyed in Teknaf. Three people died of stroke while attempting to recover their salt farm on Maheshkhali Island. There and in other upazilas, between 50 and 60 houses were damaged. Agricultural damage in Cox's Bazar District reached ৳115 million (US$1.07 million). Mocha's Gale-force winds began to blow in Bangladesh, accompanied by heavy rainfall. Heavy rains in Bangladesh, according to officials, caused damage in several regions.
Sri Lanka.
Although the impact of the cyclone on Sri Lanka was significantly reduced by its landfall between Bangladesh and Myanmar, seven people were injured, another seven were reported missing, and nearly 2,000 people have been affected in Southern Sri Lanka due to the cyclonic storm's indirect influence. The Sri Lanka Navy (SLN) has deployed approximately 30 relief teams to assist those affected by potential floods.
India.
The India Meteorological Department (IMD) said that the southeast Bay of Bengal region of Tripura, Mizoram, Nagaland, southern Assam, and portions of Manipur were