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Meteorological history of Cyclone Freddy
Cyclone Freddy was the longest-lived tropical cyclone, lasting five weeks and three days, surpassing the previous record holder, 1994's Hurricane John. It also had the highest accumulated cyclone energy, a metric used to measure tropical cyclone activity, ever recorded worldwide. It also featured a record seven separate rounds of rapid intensification during February and March 2023. Freddy originated from a tropical low south of the Indonesian archipelago early on 4 February. Deep convection soon developed, and the system intensified Category 1 tropical cyclone on the Australian scale on 6 February. Located just within Tropical Cyclone Warning Centre Melbourne's area of responsibility, the storm was named Freddy—the third named storm of the 2022–23 Australian region cyclone season—by the Australian Bureau of Meteorology. As it moved westward across the Indian Ocean, Freddy quickly intensified and became a Category 4 severe tropical cyclone before it moved into the area of responsibility of Météo-France La Réunion. As the second very intense tropical cyclone of the 2022–23 South-West Indian Ocean cyclone season. Freddy peaked with 10-minute sustained winds of 230 km/h (145 mph) and a central barometric pressure of 927 hPa (27.37 inHg). It quickly strengthened, reaching 1-minute sustained winds of 270 km/h (165 mph), making it a Category 5-equivalent intensity on the Saffir–Simpson scale. After briefly weakening from its peak intensity, the cyclone moved toward the northern Mascarene Islands. It then developed a pinhole eye while approaching Madagascar as a compact tropical cyclone. The cyclone then made landfall as a strong Category 2-equivalent intensity with 1-minute sustained winds of 175 km/h (110 mph) near Mananjary, Madagascar on 21 February. This made Freddy the strongest storm to impact the island nation since Cyclone Batsirai a year earlier. It weakened further as it moved overland but regained strength upon reaching the Mozambique Channel. The cyclone intensified into a severe tropical storm and then passed north of Europa Island. The cyclone then made its second landfall near Vilankulos, Mozambique, as a moderate tropical storm status on 24 February. Upon re-entering the channel early on 1 March, it began regaining tropical characteristics and meandering along the Madagascar coast. It then intensified into a tropical cyclone with winds of about 175 km/h (110 mph) before making its final landfall near Quelimane, Mozambique on 11 March. Thereafter, it gradually weakened and dissipated late on 14 March. Formation and intensification The origins of Cyclone Freddy can be traced back to 4 February 2023, when the Australian Bureau of Meteorology (BoM)[nb 1] reported that a tropical low—identified as 13U—had formed during an active phase of the Madden–Julian oscillation in conjunction with an equatorial Rossby wave,[2] while it was situated to the south of the Indonesian archipelago.[3] Soon after, the United States Joint Typhoon Warning Center (JTWC)[nb 2] issued a tropical cyclone formation alert, noting that the disturbance was located in a favorable environment with low wind shear and sea surface temperatures of 29–30 °C (84–86 °F).[5] Early on 6 February, the JTWC began issuing warnings on the system, classifying it as Tropical Cyclone 11S.[6] Deep convection increased and the system became a Category 1 tropical cyclone on the Australian scale by 12:00 UTC; the BoM assigned it the name Freddy accordingly.[2][7] Freddy then rapidly intensified and developed an eye feature on microwave imagery. As a result, the JTWC classified it as a Category 2-equivalent intensity on the Saffir-Simpson scale around 15:00 UTC on 7 February.[8] After its first peak, the system became increasingly susceptible to wind shear and dry air intrusion,[9] causing Freddy to weaken back into a minimal tropical storm by 09:00 UTC on 9 February.[10] Freddy's deep convection around the storm's center had significantly decreased.[2] Atmospheric conditions became more favorable for development as wind shear decreased and deep convection began to consolidate and wrap around the cyclone.[2] Consequently, the cyclone quickly restrengthened with the storm becoming a Category 3 severe tropical cyclone—attaining an initial peak intensity with winds of 150 km/h (90 mph)—and at 18:00 UTC on 11 February, Freddy reached its second peak intensity as a high-end Category 4 severe tropical cyclone in the Australian basin, with winds of 175 km/h (110 mph) and a central barometric pressure of 951 hPa (28.08 inHg).[2] The cyclone's eyewall displayed cloud tops warming to below −130 °F (−90 °C) while passing over warm sea surface temperature of 29 °C (84 °F).[11] The cyclone's structure continued to gradually weaken before moving over the South-West Indian Ocean.[2] At around 12:00 UTC on 14 February, the BoM passed the responsibility of tracking the system over to the Météo-France office on La Réunion (MFR).[nb 3] Thus, the system was initially classified as a tropical cyclone status before being later upgraded to intense tropical cyclone status around 18:00 UTC that day.[13][14] A 2023 study published by the American Geophysical Union found that Freddy's southwestward trajectory was driven by a northerly steering flow caused by its interaction with Cyclone Dingani to the west.[15] The Mascarene Islands, Madagascar, and Mozambique Cyclone Freddy acquired annular characteristics on 14 February, bearing a symmetrical appearance and a well-defined 11.5 miles (18.5 km) wide pinhole eye, which was largely surrounded by central dense overcast.[16] On 15 February at 03:00 UTC, the JTWC reported that the cyclone re-strengthened and underwent another period of rapid intensification, reaching Category 4-equivalent intensity;[17] post-analysis by the JTWC revealed that the cyclone had already reached Category 5-equivalent intensity,[18] with 1-minute sustained winds of 270 km/h (165 mph).[19] After maintaining Category 5 intensity for about 12 hours, Freddy weakened slightly before restrengthening back to Category 5 intensity on 19 February.[18] The cyclone's cloud tops warmed to −101 °F (−74 °C),[20] causing the system to display annular characteristics. Additionally, the storm's eye expanded to a diameter of 29 miles (46 km).[21] Concurrently, the cyclone was assigned a T7.0 rating via the Dvorak technique—a method of determining a tropical cyclone's intensity based on satellite appearance.[20] Around 00:00 UTC that day, the MFR upgraded Freddy to a very intense tropical cyclone estimated a minimum barometric pressure of 931 hPa (27.49 inHg) and 10-minute sustained winds of 220 km/h (140 mph).[20] However, in the best track for Freddy, the MFR concluded a peak wind speed of 230 km/h (145 mph), and minimum central pressure of 927 hPa (27.37 inHg).[22] The cyclone then turned west-southwestward, along the northern edge of a mid-level subtropical high.[23] After reaching its peak intensity, the cyclone's eye pattern quickly deteriorated as the cloud tops warmed on 20 February, while it was traversing north of the Mascarene Islands.[24] Later, an eyewall replacement cycle occurred,[25] causing the storm to weaken.[26] Late on 21 February, the cyclone developed a well-defined 7 miles (11 km) pinhole eye while approaching Madagascar as a compact tropical cyclone.[27] Around 18:00 UTC that day, the cyclone made landfall near Mananjary, Madagascar,[28] with the JTWC estimating winds of 175 km/h (110 mph).[29] This made Freddy the strongest storm to impact the island nation since Cyclone Batsirai a year earlier.[30] It then rapidly weakened upon encountering the mountainous terrain of the island nation and was downgraded to overland depression status.[31] After crossing Madagascar, the cyclone's circulation became exposed, and deep convection was stripped away from the center on 22 February.[32] Moving west-northwestward in response to a subtropical ridge to the west,[33] Freddy emerged over the Mozambique Channel on 23 February.[34] Afterwards, the cyclone's convection increased in the northern semicircle, and by around 06:00 UTC, Freddy had strengthened into a moderate tropical storm.[35] Steered by a subtropical ridge to the south,[36] the cyclone moved westward and quickly intensified into a severe tropical storm around 12:00 UTC that day, with convection wrapping around its center.[37] An automated weather station on Europa Island indicated that Freddy had wind gusts up to 93–111 km/h (58–69 mph) after passing north of the island.[38] Around 12:00 UTC on 24 February, the storm made landfall in Mozambique south of Vilankulos, with winds about 85 km/h (50 mph), just below severe tropical storm strength.[39] It then rapidly weakened as it moved westward and further inland, eventually weakening to overland depression status around 18:00 UTC that day.[40] The system's convective activity was concentrated in the southeastern semicircle over Mozambique on 25 February.[41] Freddy's remnant low continued moving into Zimbabwe late on 26 February, where it stayed for a couple of days.[42] Redevelopment and dissipation  Freddy was intensifying off the coast of Madagascar on 7 March (left) and remained nearly stationary off the coast of Mozambique on 11 March (right). As early as 26 February, the MFR anticipated that a large low-pressure circulation associated with Freddy would move back toward the coast of Mozambique due to the influence of a trough over the southern Mozambique Channel and a near-equatorial ridge to the north.[42] Projections from computer models also indicated that the system would redevelop into a tropical cyclone.[43] Early on 1 March, Freddy emerged again into the channel—benefiting from favorable environmental conditions such as low vertical wind shear, good upper-level divergence,[44] and sea surface temperatures of 28–29 °C (82–84 °F).[45] The cyclone drifted slowly southward and struggled to intensify due to its broad circulation.[46] At 06:00 UTC on 4 March, the MFR upgraded the system to a moderate tropical storm after an advanced scatterometer showed winds of 44 km/h (25 mph) in the southern semicircle.[47] It was also noted that Freddy was tracking towards the eastward—under the increasing influence of the near-equatorial ridge to the north—as it developed a consolidating low-level circulation.[48] The cyclone further intensified strengthened into a severe tropical storm status as it accelerated eastward toward the coast of Madagascar early on 5 March.[49] Meandering along the Madagascar coast,[50] the cyclone unexpectedly intensified—developing an ill-defined eye—which prompted the MFR to upgrade it to tropical cyclone status with sustained winds of 150 km/h (90 mph) by 12:00 UTC on 7 March.[51] Freddy's eye disappeared from satellite imagery six hours later due to the effects of southern wind shear.[52] The cyclone's motion accelerated and shifted northwestward under the northeastern side of the steering subtropical ridge early on 9 March.[53] The cyclone rapidly weakened to slightly below minimal tropical storm strength due to increased wind shear and dry air intrusion.[53] Despite this,[54] the cyclone managed to steadily quickly—developing banding features.[55] The cyclone rapidly re-strengthened and made landfall for the final time near Quelimane, Mozambique at 18:00 UTC on 11 March,[56] with the JTWC estimated winds of about 175 km/h (110 mph)[57]—featured a well-defined eye within its compact and symmetrical dense overcast.[58] Within two hours, the eye of Freddy disappeared from satellite imagery, and it was estimated to have fallen below tropical cyclone status on 12 March.[59] The JTWC described the cyclone as "a B-reel horror movie that never ends", and concluded, "It may not stay overland for long."[54] The computer models predicted that the cyclone would turn eastward and re-emerge in the channel;[60] however, it ultimately moved northwestward inland,[54] bringing rain to Malawi and Mozambique before dissipating on 14 March.[22] RecordsFreddy's 36-day duration makes it the longest-lasting tropical cyclone to be recorded worldwide, in terms of the number of days maintaining tropical storm status or higher, surpassing Hurricane John's previous record of 31-days in the 1994 season.[3] Additionally, Freddy was the second-farthest traveling tropical cyclone globally, covering a distance of 12,785 km (7,945 mi), which is approximately 33% of the Earth's circumference—just shy of 1994's Hurricane John, which covered 13,180 km (8,190 mi).[3] In addition, it achieved the highest accumulated cyclone energy—a metric used to measure the total energy generated by tropical cyclones—of any tropical cyclone worldwide, with a total of 87.01, exceeding the previous record set by Hurricane Ioke in 2006.[61] It later became the first tropical cyclone to undergo seven separate rounds of rapid intensification.[62] It exceeded the previous records held by Hurricane Norman in 2018, Hurricane Emily in 2005, and 1994's Hurricane John.[63] Further, it was one of only four systems to traverse the entirety of the southern Indian Ocean from east to west; the others were Cyclone Litanne in 1994 as well as Cyclone Leon-Eline and Cyclone Hudah in 2000.[64] See also
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