The 2018 North Indian Ocean cyclone season was one of the most active North Indian Ocean cyclone seasons since 1992, with the formation of fourteen depressions and seven cyclones. The North Indian Ocean cyclone season has no official bounds, but cyclones tend to form between April and December, with the two peaks in May and November. These dates conventionally delimit the period of each year when most tropical cyclones form in the northern Indian Ocean.
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. There are two main seas in the North Indian Ocean — the Arabian Sea to the west of the Indian subcontinent, abbreviated ARB by the India Meteorological Department (IMD); and the Bay of Bengal to the east, abbreviated BOB by the IMD. The systems that form over land are abbreviated as LAND.
The official Regional Specialized Meteorological Centre in this basin is the IMD, while the Joint Typhoon Warning Center (JTWC) and the National Meteorological Center of CMA (NMC) unofficially release full advisories. On average, three to four cyclonic storms form in this basin every season.
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Season summary
The season started with ARB 01 which was formed on March 14 making one of the rarest system formed in March since tropical cyclone development stays relatively low between January and March. It caused heavy rainfall in Maldives, Lakshadweep and Kerala. After a two-month gap, another low formed near the Horn of Africa, which later became Sagar. It became unofficially the strongest cyclone to make landfall until it was broken by Gati in 2020. It caused heavy rainfall in Somaliland and local flooding was reported in the Yemeni coast. The storm made the westernmost landfall surpassing the record of Tropical Storm One. A day after Sagar dissipation, another low pressure formed off the coast of Oman which later organised into Cyclone Mekunu. It then peaked as a Category 3 tropical cyclone according to JTWC and an Extremely Severe Cyclonic Storm according to IMD. It caused 30 people dead and heavy rainfall recorded in Salalah, Oman. After that, a low pressure quickly intensified into a deep depression and peaking as a tropical storm made landfall in Myanmar causing heavy downpour. Five monsoonal depression also formed between June and September, all of them were land depressions.
Cyclogenesis continued with Cyclone Daye which made landfall in Odisha state. Heavy downpour and flood mainly in Malkangiri district and its outer bands also caused heavy rainfall in West Bengal. Following with Daye, Luban and Titli both formed in the Arabian sea and the Bay of Bengal respectively, causing heavy damages in Oman and Andhra Pradesh. Gaja on November 10, also formed and caused extensive damage in Tamil Nadu and Andaman and Nicobar Islands. The season ended with Cyclone Phethai causing agricultural damage and four dead.
Systems Depression ARB 01
A trough developed near the equator in the eastern Indian Ocean on March 7. A low-pressure area formed on March 10 to the southwest of Sri Lanka, in an area with warm sea surface temperatures and low wind shear. Moving into the eastern Arabian Sea, the low organized into a depression on March 13 at the low latitude of 5° N. After its formation, the depression encountered cooler, drier air, which prevented the system from strengthening beyond an intensity of . Moving northwest, the depression passed between the Maldives and the Lakshadweep islands, and weakened into a remnant low-pressure area on March 15.
Officials advised fishermen to avoid sailing off India's southwest coast for a few days. The depression produced heavy rainfall across southern India. The coastal port city of Thoothukudi near the southern tip of India recorded on March 13, its highest daily precipitation ever recorded. Minicoy Island in Lakshadweep received of rain from the system. Heavy rainfall also occurred in Aryankavu, Kerala, and Chintamani, Karnataka.
Cyclonic Storm Sagar
A low-pressure area formed on May 14 near Socotra in the western Arabian Sea. The weather system moved northwestward, steered by a ridge to the northeast and the flow of the regional geography. On May 16, the India Meteorological Department (IMD) classified the low as a depression at 12:00 UTC about northeast of Cape Guardafui, Somalia. On the same day, the JTWC designated the depression as Tropical Cyclone 01A. The IMD upgraded the system to a cyclonic storm on May 17, naming it Sagar. The storm entered the Gulf of Aden that day, gradually intensifying while paralleling the coast of Yemen. Sagar developed an eye on microwave imagery, a sign of an intensifying storm. Late on May 18, the IMD estimated Sagar's peak intensity at . Around the same time, the JTWC estimated Sagar attained peak 1 minute sustained winds of , while located about south of Aden, Yemen, or about north of Berbera, Somalia. Sagar weakened slightly before it made landfall near Lughaya in northwestern Somaliland, with winds of according to the IMD. According to the JTWC, Sagar was the strongest tropical cyclone on record to strike Somalia, with estimated 1-minute landfalling winds of . The storm also made the westernmost landfall in the North Indian Ocean, surpassing a tropical storm in 1984, which took a nearly identical track to the east. Sagar rapidly weakened over land, degenerating into a low-pressure area over eastern Ethiopia on May 20.
The cyclone first affected Socotra, and later the Yemeni mainland, producing locally heavy rainfall and flooding. High winds from Sagar contributed to a house fire near Aden, resulting in one fatality. In parts of northern Somalia and Somaliland, Sagar dropped a years' worth of heavy rainfall, or around , resulting in deadly flash flooding. The floods washed out farms, livestock, boats, and houses, forcing families to evacuate. Roads, medical facilities, and other infrastructure were also damaged. Three people died in Puntland and another 50 people died in Somaliland due to Sagar. In neighboring Djibouti, flooding from the storm damaged about 10,000 houses, with damage in the country estimated at US$30 million. Two people died in the country. In the Somali Region of eastern Ethiopia, Sagar produced strong winds and heavy rainfall, resulting in flooding and landslides. Near the border of SNNPR and Oromia, a landslide killed 23 people.
Extremely Severe Cyclonic Storm Mekunu
An area of convection developed to the northwest of the Maldives on May 18. Over the next two days, it became better organized and the IMD reported that it had developed into a low-pressure area on May 20, giving it the identifier ARB 03. The system slowly drifted northwestwards into favorable environment for tropical cyclogenesis and developed good outflow. The JTWC issued a TCFA on May 21 after convective bands began to wrap into the broad low-level circulation center (LLCC). Around the same time, the IMD had announced that the system intensified into a depression. Over the next 24 hours, the depression continued to drift further northwestwards into warm waters and faced low vertical wind shear. As a result, it continued to intensify and the JTWC began tracking it as a tropical storm. Subsequently, the IMD upgraded it to a deep depression and Cyclonic Storm Mekunu later the same day. Multi-spectral satellite imagery revealed that Mekunu had developed an eye as early as May 23, at which time the IMD upgraded it to a severe cyclonic storm. Benefiting from favorable environmental conditions, the cyclone became more symmetric, intensifying into a very severe cyclonic storm six hours later. The cyclone continued to track northwestward under the influence of a subtropical ridge. On May 25, it reached its peak intensity as an extremely severe cyclonic storm, with the JTWC estimating peak 1-minute sustained winds of , equivalent to a Category 3 storm on the Saffir–Simpson scale.
Under the influence of Mekunu, Socotra received widespread rainfall leading to flash flooding and downed power lines. At least 40 people were initially reported to be missing after two ships were capsized off Socotra. Mekunu made landfall on the Omani coast near the city of Salalah at peak intensity. Gusts of were recorded at the Salalah Airport before the landfall while areas in the Salalah recorded rainfall of . As of 31 May, at least 30 people have died in Oman and Yemen due to Mekunu, including 20 on Socotra, four in Yemen, and six in Oman. Insurance claims in Oman reached ﷼108 million (US$281 million).
Deep Depression BOB 01 (03B)
On May 28, a low-pressure area formed over the eastern Bay of Bengal, three days after the IMD first mentioned such a possibility. That day, the JTWC noted a low chance for development, before raising it to a medium chance. The system moved northeastward and organized, becoming a depression at 06:00 UTC on May 29. With warm waters and low wind shear, the system strengthened further. The IMD upgraded the system to a deep depression at 12:00 UTC on May 29, estimating peak winds of . The JTWC meanwhile estimated peak winds of , designating the system as Tropical Cyclone 03B; however, the agency did not issue any advisories on the cyclone in real time. Late on May 29, the deep depression moved ashore northern Myanmar near Kyaukphyu, and it rapidly weakened over land, degenerating into a low on May 30.
While in its formative stages, the depression brought heavy rainfall to the Andaman and Nicobar Islands, with a peak daily total of recorded in Port Blair. The storm later brought heavy rainfall to northeast India. Ahead of the depression's landfall, Myanmar's Meteorology and Hydrology Department issued a red-code emergency alert warning. High winds and heavy rains destroyed more than 500 homes in the Yangon region, with shelters opened for residents left homeless. The strong wind knocked down trees, cutting power supply in areas.
Depression LAND 01
A monsoonal low formed in the northern Bay of Bengal on June 8, which was anticipated by the IMD as early as June 3. Low wind shear and warm waters fueled development as the system moved to the north-northwest. On June 10, the system organized into a depression near the coastline of Bangladesh, with peak winds of . A few hours after its formation, the depression moved ashore the country south of Feni. Due to land interaction, the system weakened into a low at 00:00 UTC on June 11.
The depression brought heavy rainfall to Bangladesh and across eastern India. Sabroom in northeastern India recorded of rainfall over two days. In Bangladesh, two-day rainfall totals reached , causing flooding and landslides. The flooding closed some roads and forced more than 29,000 people to be evacuated. At least 12 people died related to the floods, including two people in Rohingya refugee camps in southeastern Bangladesh. Nearly 900 refugee camps were damaged, along with 200 latrines, two health facilities, and two food distribution centers. Heavy rains also caused flooding in the port city of Chittagong.
Depression LAND 02
A monsoonal low formed on July 19 in the northern Bay of Bengal. With favorable conditions such as warm water temperatures, the system gradually organized, becoming a depression on July 21 just off the coast of eastern India. The system only attained peak winds of , as it soon after moved ashore the Indian coastline near the borders of Odisha and West Bengal. Continuing to the northwest, the depression maintained a flow of moisture that helped sustain its intensity for 36 hours over land, before the system weakened into a low on July 23 over Jharkhand. The depression dropped torrential rainfall over eastern India, reaching as far west as Rajasthan. The highest 24 hour total was in Burla in Odisha, resulting in flooding. Flood-related incidents killed five people in Odisha.
Depression LAND 03