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Cyclone Chapala

North Indian cyclone in 2015

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While Chapala encountered less favorable conditions after passing Socotra, it maintained much of its intensity; upon entering the Gulf of Aden on 2 November, it became the strongest known cyclone in that body of water. Chapala brushed the northern coast of Somalia, killing tens of thousands of animals and wrecking 350 houses. Ahead of the cyclone's final landfall, widespread evacuations occurred across southeastern Yemen, including in areas controlled by al-Qaeda, amid the country's ongoing civil war. Early on 3 November, the storm made landfall near Mukalla, Yemen, as a very severe cyclonic storm and the strongest storm on record to strike the nation. Chapala weakened into a remnant low the next day overland. Several years' worth of heavy rainfall inundated coastal areas, damaging roads and hundreds of homes. Eight people died in Yemen, a low total credited to the evacuations, and another 65 were injured. After cyclones Chapala and Megh, several countries, non-government organizations, and agencies within the United Nations provided monetary and material assistance to Yemen. The country faced food and fuel shortages, and residual storm effects contributed to an outbreak of locusts and dengue fever, the latter of which killed seven people.

Meteorological history

The monsoon trough spawned a fragmented area of convection, or thunderstorms, southwest of India on 25 October, 2015. The system was located within an environment of moderate wind shear, which prevented early development but decreased over time. On 26 October, the system developed a distinct low-pressure area, which gradually became better defined, with good outflow to the north and south. At 03:00 UTC on 28 October, the India Meteorological Department (IMD) designated the system as a depression. Nine hours later, the agency upgraded it to a deep depression, and the Joint Typhoon Warning Center (JTWC) classified the system as Tropical Cyclone 04A at 21:00 UTC.

The deep depression moved slowly to the north at first, steered by an anticyclone to the northeast. The IMD upgraded the system to a cyclonic storm at 00:00 UTC on 29 October, giving it the name Chapala. Around the same time, the storm turned towards the west, influenced by another anticyclone to its northwest. With low wind shear, as well as record-warm 30 °C (86 °F) water temperatures, Chapala began a 33-hour period of rapid deepening, in which the barometric pressure dropped 59 hPa (1.74 inHg). The storm developed well-defined rainbands and thunderstorms that consolidated into an eye feature. The JTWC estimated Chapala attained hurricane-force winds of 120 km/h (75 mph) at 12:00 UTC on 29 October. Meanwhile, the IMD upgraded Chapala to a severe cyclonic storm at 09:00 UTC that day, and further to a very severe cyclonic storm at 18:00 UTC. By early on 30 October, Chapala had developed a well-defined eye 22 km (14 mi) wide. Based on satellite intensity estimates using the Dvorak technique, the JTWC assessed Chapala as a high-end Category 4-equivalent cyclone on the Saffir–Simpson hurricane wind scale at 06:00 UTC with one-minute sustained winds of 240 km/h (150 mph). Based on their estimate, Chapala was the second-strongest cyclone on record over the Arabian Sea; at the time, only Cyclone Gonu of 2007 was stronger, and Cyclone Kyarr tied it in 2019. Meanwhile, the IMD upgraded Chapala to an extremely severe cyclonic storm at 00:00 UTC on 30 October and estimated peak three-minute sustained winds of 215 km/h (135 mph) at 09:00 UTC. The agency estimated a minimum central pressure of 940 hPa (27.76 inHg).

At the time of peak intensity, Chapala was moving to the west-southwest due to a ridge to the north. Initially, the IMD forecast that Chapala would intensify further into a super cyclonic storm, and the JTWC anticipated it strengthening into a Category 5-equivalent. Instead, the storm began an eyewall replacement cycle on 30 October, causing the inner eyewall to degrade and an outer eyewall to form; this resulted in a slight drop in intensity. As well, drier air began affecting the storm, causing the thunderstorms around the eye to diminish. Chapala maintained much of its intensity due to strong outflow in all directions, especially to the northeast due to a tropical upper tropospheric trough over India, despite increased wind shear. The new eyewall became established on 31 October, reaching a diameter of 37 km (23 mi), although the thunderstorms around the eye continued to weaken. On 1 November, Chapala passed just north of the island of Socotra, marking the island's first hurricane-force impact since 1922.

After the cyclone passed Socotra, its convective core became better-defined due to improved outflow. Chapala entered the Gulf of Aden on 2 November, becoming the strongest tropical cyclone on record in that region. At 12:00 UTC that day, the IMD downgraded the system to a very severe cyclonic storm, after Chapala had been an extremely severe cyclonic storm for 78 hours. The structure became disorganized due to increased easterly wind shear and interaction with the Arabian Peninsula to the north, allowing cooler and drier air to enter the circulation. Around this time, the storm began moving more to the west-northwest toward Yemen, rounding the southwestern periphery of a ridge. Between 01:00–02:00 UTC on 3 November, Chapala made landfall near Mukalla with winds of 120 km/h (75 mph). This marked the first Yemeni hurricane-intensity landfall on record, and the first severe cyclonic storm to hit the country since May 1960. The center straddled the coast before heading inland. Chapala quickly weakened over land, degenerating into a depression by 00:00 UTC on 4 November and weakening into a remnant low-pressure area three hours later.

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