Meteorological history of Cyclone Freddy

Cyclone Freddy was the longest-lived tropical cyclone, lasting five weeks and three days, surpassing the previous record holder, 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 2023–24 Australian region cyclone season—by the Australian Bureau of Meteorology. 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 2023–24 South-West Indian Ocean cyclone season. Freddy peaked with 10-minute sustained winds of 125 kn and a central barometric pressure of 927 hPa. It quickly strengthened, reaching 1-minute sustained winds of 145 kn, making it a Category-5 equivalent intensity.

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 winds about 95 kn near Mananjary, Madagascar on 21 February. 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 early on 24 February. Upon re-emerging into the channel early on 1 March, it began to regain tropical characteristics—meandering along the Madagascar coast—and intensified into a below tropical cyclone just before making its final landfall with winds of about 95 kn 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) 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, while it was situated to the south of the Indonesian archipelago. Soon after, the United States Joint Typhoon Warning Center (JTWC) issued a tropical cyclone formation alert, noting that the disturbance was located in a favourable environment with low wind shear and sea surface temperatures of 29-30 C. Early on 6 February, the JTWC began issuing warnings on the system, classifying it as Tropical Cyclone 11S. Deep convection increased and the system became a Category 1 tropical cyclone on the Australian scale by 12:00 UTC; the Australian Bureau of Meteorology (BoM) assigned it the name Freddy accordingly. 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 around 15:00 UTC on 7 February. After its first peak, the system became increasingly susceptible to wind shear and dry air intrusion, causing Freddy to weaken back into a minimal tropical storm by 09:00 UTC on 9 February. Freddy's deep convection around the storm's center had significantly decreased.

Atmospheric conditions became more favorable for development as wind shear decreased and deep convection began to consolidate and wrap around the cyclone. Consequently, the cyclone quickly restrengthened with the storm becoming a Category 3 severe tropical cyclone—attaining an initial peak intensity with winds of 80 kn—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. The cyclone's eyewall displayed cloud tops warming to below -90 C while passing over warm sea surface temperature of 29 C. The cyclone's structure continued to gradually weaken before moving over the South-West Indian Ocean. 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). 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.

The Mascarene Islands, Madagascar, and Mozambique
Cyclone Freddy acquired annular characteristics on 14 February, bearing a symmetrical appearance and a well-defined 10 km wide pinhole eye, which was largely surrounded by central dense overcast. 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; however, post-season analysis determined that it had attained 1-minute sustained winds of 145 kn—making Freddy equivalent to a Category 5 intensity. After maintaining Category 5 intensity for about 12 hours, Freddy weakened slightly before restrengthening back to Category 5 intensity on 19 February. It then strengthened further to its peak intensity as a very intense tropical cyclone—the highest rating on the MFR's classification scale—with 10-minute sustained winds of 125 kn and the lowest atmospheric pressure of 927 hPa.

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. Later, an eyewall replacement cycle occurred, causing the storm to weaken. Late on 21 February, the cyclone developed a well-defined 6 mi pinhole eye while approaching Madagascar as a compact tropical cyclone. By 18:00 UTC that day, the cyclone made landfall near Mananjary, Madagascar, with the JTWC estimated winds of about 95 kn. It then rapidly weakened upon encountering the mountainous terrain of the island nation and was downgraded to overland depression status. After crossing Madagascar, the cyclone's circulation became exposed, and deep convection was stripped away from the center on 22 February. Upon emerging over the Mozambique Channel by 23 February, the system had strengthened to attain moderate tropical storm—aided by favorable environmental conditions—with deep convection in the northern semicircle of the circulation. Steered by a subtropical ridge to the south, the cyclone moved westward and quickly intensified into a severe tropical storm around 12:00 UTC that day, with convection wrapping around its center. An automated weather station on Europa Island indicated that Freddy had wind gusts up to 50-60 kn after passing north of the island. Around 12:00 UTC on 24 February, the storm made landfall in Mozambique south of Vilankulos, with winds about 45 kn, just below severe tropical storm strength. It then rapidly weakened as it moved westward and further inland, eventually weakening to overland depression status around 18:00 UTC that day. The system's convective activity was concentrated in the southeastern semicircle over Mozambique on 25 February. Freddy's remnant low continued moving into Zimbabwe late on 26 February, where it stalled for a couple of days.

Redevelopment and demise
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. Projections from computer models also indicated that the system would redevelop into a tropical cyclone. 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, and sea surface temperatures of 28-29 C. The cyclone drifted slowly southward and struggled to intensify due to its broad circulation. At 06:00 UTC on 4 March, the MFR upgraded the system to a moderate tropical storm after an advanced scatterometer (ASCAT) showed winds of 44 km/h in the southern semicircle. 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. The cyclone further intensified strengthened into a severe tropical storm status as it accelerated eastward toward the coast of Madagascar early on 5 March.

Meandering along the Madagascar coast, the cyclone unexpectedly intensified—developing an ill-defined eye—which prompted the MFR to upgrade it to tropical cyclone status with sustained winds of 80 kn by 12:00 UTC on 7 March. Moving steadily northwestward early on 9 March, the cyclone rapidly weakened to slightly below minimal tropical storm strength due to increased wind shear and dry air intrusion. Despite this, the cyclone managed to steadily quickly—developing banding features. The JTWC described the system as "a B-reel horror movie that never ends" and concluded, "I Am Legend," while meteorologists described it as "remarkable." The cyclone rapidly re-strengthened and made landfall for the final time near Quelimane, Mozambique at 03:00 UTC on 11 March, with the JTWC estimated winds of about 95 kn—featured a well-defined eye within its compact and symmetrical dense overcast. Within two hours, the eye of Freddy disappeared from satellite imagery, and it was estimated to have fallen below tropical cyclone status at 12:00 UTC on 12 March. Initial computer models predicted the cyclone would turn eastward and re-enter the channel. However, the storm's circulation dissipated, marking the cessation of Freddy's time as a tropical cyclone on 14 March. Late that same day, the system continued to travel northwards, bringing rain to Malawi and Mozambique.

Records
Freddy's 36-day existence made it the longest-lasting tropical cyclone recorded worldwide, surpassing Hurricane John's previous record in the 1994 season. Additionally, Freddy was the second-farthest traveling tropical cyclone globally, behind 1994's Hurricane John, covering a distance of 12,785 km, which is approximately 33% of the Earth's circumference. Moreover, it achieved the highest accumulated cyclone energy, a metric used to measure tropical cyclone activity. reaching an ACE of 87.01, equivalent to an average Atlantic hurricane season, and surpassing the previous record set by Hurricane Ioke in 2006. It later became the first tropical cyclone to undergo seven separate rounds of rapid intensification. It exceeded the previous records held by Hurricane Norman in 2018, Hurricane Emily in 2005, and 1994's Hurricane John. 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 Hudah in 2000.