The 2020–21 South Pacific cyclone season was an average season where most tropical cyclones formed within the South Pacific Ocean to the east of 160°E. The season officially started on November 1, 2020, and officially ended on April 30, 2021, however a tropical cyclone could form at any time between July 1, 2020, and June 30, 2021, and would count towards the season total. During the season, tropical cyclones will be officially monitored by the Fiji Meteorological Service (FMS), Australian Bureau of Meteorology (BoM), New Zealand's MetService. The United States Armed Forces through the Joint Typhoon Warning Center (JTWC) will also monitor the basin and issue unofficial warnings for American interests. RSMC Nadi attaches a number and an F suffix to tropical disturbances that form in or move into the basin while the JTWC designates significant tropical cyclones with a number and a P suffix. RSMC Nadi, TCWC Wellington and TCWC Brisbane all use the Australian Tropical Cyclone Intensity Scale and estimate windspeeds over a period of ten minutes, while the JTWC estimated sustained winds over a 1-minute period, which are subsequently compared to the Saffir–Simpson hurricane wind scale (SSHWS).
The season began with the formation of Tropical Depression 01F, over a month after the official start. Despite the slightly late start, activity picked up, with two more systems forming after. In mid-December, Severe Tropical Cyclone Yasa became the earliest category 5 severe tropical cyclone on record in the South Pacific basin. Yasa struck Fiji, resulting in heavy damage. Severe Tropical Cyclone Ana and Tropical Cyclone Bina also affected Fiji within days of each other, resulting in heavy rains and strong winds. Tropical Cyclone Lucas crossed into the basin from the Australian region and affected the Loyalty Islands. In early March, Cyclone Niran moved into basin from the Australian region as a Category 5 severe tropical cyclone. The storm passed close to New Caledonia, bringing heavy impact, before transitioning into an extratropical cyclone north of New Zealand.
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Seasonal forecasts Source/Record TropicalCyclone SevereTropical Cyclone Ref Record high: 1997–98: 16 1982–83: 10 Record low: 1990–91: 2 2008–09: 0 Average (1969–70 – 2019–20): 7 3 NIWA October 8–10 3–4 Fiji Meteorological Service 4–6 1–3
Ahead of the season officially starting on November 1, the Fiji Meteorological Service (FMS) and New Zealand's National Institute of Water and Atmospheric Research (NIWA), both issued a tropical cyclone outlook that discussed the upcoming season. These outlooks took into account a variety of factors such as a developing weak to moderate La Niña event and what had happened in previous seasons such as 1970–71, 1984–85, 1995–96, 2007–08, 2016–17 and 2017–18. The Southwest Pacific tropical cyclone outlook issued by New Zealand's National Institute of Water and Atmospheric Research (NIWA) in conjunction with MetService and various other Pacific meteorological services, predicted that nine to twelve tropical cyclones would occur over the South Pacific Ocean between 135°E and 120°W. The outlook also predicted that four of these tropical cyclones would intensify further and become either a Category three, four or five severe tropical cyclone on the Australian tropical cyclone intensity scale. In addition to contributing towards the Southwest Pacific tropical cyclone outlook, the FMS predicted that between four and six tropical cyclones would occur within the basin, while one of these tropical cyclones was expected to intensify further and become either a category three, four or five severe tropical cyclone on the Australian scale. Both outlooks also predicted that the majority of systems would occur to the west of the International Dateline, which as a result, meant that New Caledonia had an elevated chance of being impacted by a tropical cyclone. It was also predicted that the Solomon Islands, Vanuatu, Fiji and Tokelau had a normal chance of being impacted by a tropical cyclone, while Wallis and Futuna, French Polynesia, Niue, Samoa, American Samoa, Tonga and Tuvalu all had a normal to reduced chance of being impacted by a tropical cyclone.
Seasonal summary
On December 8, a disturbance formed near Fiji, starting the 2020–21 South Pacific Ocean cyclone season, it gradually intensified into a depression and attained a tropical storm status according to JTWC. It reached at the maximum 10 minutes sustained wind speed of and minimum pressure of . Another disturbance formed near the existing 01F and rapidly intensified into a depression. It hampered the system intensification due to a brief interaction with Tropical Depression 01F. Following the same day, another disturbance formed and intensified into a depression the next day. 01F became a remnant low and was absorbed by Tropical Depression 02F. On December 13, 15:00 UTC, 02F intensified into a Category 1 tropical cyclone, giving it the name Yasa. It quickly strengthened into a Category 5 tropical cyclone before impacting Fiji. 03F intensified into Category 1 tropical cyclone Zazu, strengthening to Category 2. Yasa became the third most intense tropical cyclone of 2020, behind only Goni and Haishen with a minimum barometric pressure of and a maximum wind speed of . Yasa caused heavy damage in and four deaths in Fiji. It then became extratropical on December 20.
After all that, the basin remained quiet for a while until activity picked up in late January. Four depressions formed within a few days of each other, with two becoming named, Ana and Bina. Ana became a Category 3 tropical cyclone struck Fiji like Yasa did and caused damage in the island nation. Bina was a short-lived storm that affected Fiji and Vanuatu. Then, on February 1, Lucas entered the basin form the Australian region. It peaked as a Category 2 tropical cyclone and affected the Loyalty Islands. Afterward, another depression formed.
Another pause of inactivity ensued again, with only a small disturbance forming, in late February. However, in early March, Niran entered the basin from the Australian region as a Category 5 severe tropical cyclone. It passed close to New Caledonia before becoming extratropical north of New Zealand. The basin became quiet once again until a disturbance formed on April 9, strengthening into a depression later. Upon post-analysis data, it was updated to Category 1 tropical cyclone (Australian scale).
Systems Tropical Depression 01F
During December 8, the FMS reported that Tropical Disturbance 01F had developed about to the northeast of Apia in Samoa. At this stage, the system had a broad low level circulation and was located within a marginal environment for further development, with warm sea surface temperatures as well as moderate levels of vertical wind shear. Over the next couple of days, the system gradually moved westwards before the FMS classified it as a tropical depression during December 11, while it was located about to the west of the Fijian Dependency of Rotuma. At 00:00 UTC on December 11, the JTWC upgraded the system to a tropical storm on the Saffir–Simpson hurricane wind scale. The depression continued to consolidate, with deep convection wrapping into the centre of the system from the northern semicircle, and by 12:00 UTC, one-minute sustained winds had increased to . A few hours later, the FMS estimated maximum 10-minute sustained winds to be at , with a minimum central atmospheric pressure of . However, environmental conditions were only marginally conducive for intensification, with strong vertical wind shear inhibiting further development. By 00:00 UTC on December 12, both the JTWC and the FMS reported that the shear had displaced the system's deep convection to the northeast, leaving the center of circulation fully exposed. Due to the deteriorating structure of the system, the FMS ceased advisories on Tropical Depression 01F at this time. The storm then weakened and degenerated into a low pressure system later on December 12. Because of the Fujiwhara effect, the remnant was absorbed by Tropical Depression 02F shortly afterward, which would later become Severe Tropical Cyclone Yasa.
01F caused heavy rain in American Samoa, with a peak rainfall total of recorded at the Pago Pago International Airport.
Severe Tropical Cyclone Yasa
Tropical Disturbance 02F was first noted by the FMS on December 11, while it was located about to the northeast of Port Villa in Vanuatu. Environmental conditions were very favourable for tropical cyclogenesis, with radial outflow in the upper troposphere, low vertical wind shear, and sea surface temperatures near . Convective rainbands began to develop around the system as it tracked slowly eastwards, wrapping into the low-level circulation center. At 00:00 UTC on December 12, the Fiji Meteorological Service (FMS) upgraded the system to Tropical Depression 02F and began issuing forecast track maps. At the same time, the Joint Typhoon Warning Center (JTWC) issued a tropical cyclone formation alert for the system. The JTWC also noted a Fujiwhara interaction with 01F, which briefly hampered the development of the system. At 15:00 UTC December 12, the JTWC determined the system had strengthened into Tropical Cyclone 05P and was now producing winds up to gale force, while it absorbed the remnant of Tropical Depression 01F. About a day later, on December 13, the FMS determined that the depression had further strengthened to Category 1 status, as convection continued wrapping into the center, with the storm acquiring the name Yasa. Soon afterwards, the JTWC upgraded Yasa to a Category 1-equivalent cyclone on the Saffir–Simpson scale.
The storm continued to intensify and soon became a Category 3 on the Australian scale. Just about 12 hours later on December 14, Yasa rapidly intensified to Category 4 status on the Australian scale as a defined eye began to clear on infrared satellite imagery. The storm continued rapidly intensifying and strengthened to a Category 5 tropical cyclone on the Australian scale, the highest rating possible, while completing its loop, with a central pressure of 929 mbar and wind speeds of 110 knots (125 mph). This was the earliest date a Category 5 South Pacific tropical cyclone formed on record and only the second Category 5 South Pacific tropical cyclone recorded in December. Yasa continued its rapid intensification trend and further intensified to the equivalent of a high-end Category 4 tropical cyclone on the Saffir–Simpson scale (SSHWS), developing a well-defined and obvious eye, while continuing to become more symmetrical. By 00:00 UTC on December 16, Yasa had intensified into a Category 5-equivalent tropical cyclone on the SSHWS, with 1-minute sustained winds of . At 18:00 UTC, Yasa's maximum 10-minute sustained winds increased to , with a minimum atmospheric pressure of 917 hPa (27.08 inHg), making the system one of the most intense tropical cyclones ever recorded in the Southern Hemisphere. After making landfall on Vanua Levu, Yasa moved into an area of unfavorable conditions, causing the storm to rapidly weaken, with Yasa weakening into a Category 3 severe tropical cyclone later that day. Yasa continued its weakening trend as it turned southward, dropping to Category 1 tropical cyclone status in late December 18. Late on December 19, Yasa transitioned into an extratropical storm, and the FMS issued their final advisory on the storm. Afterward, Yasa's extratropical remnant moved southward and then eastward, before dissipating on December 24, to the northeast of New Zealand.
Tropical Cyclone Zazu