Earth’s second category 5 tropical storm of 2021 is Tropical Cyclone Niran in the South Pacific Ocean. Niran is expected to affect New Caledonia as a destructive category 4 storm on Saturday.
Niran took advantage of low wind shear of 5-10 knots and warm ocean temperatures of 29 degrees Celsius (84°F) to rapidly intensity by 35 mph in just six hours on Friday, peaking as a category 5 storm with 160 mph winds and a central pressure of 917 mb at 8 am EST March 5, according to the Joint Typhoon Warning Center (JTWC). Niran’s intensity was estimated via the standard Dvorak technique, which uses infrared satellite imagery.
High wind shear is expected to gradually weaken Niran, but the cyclone is expected to be at category 4 strength as it moves along the south shore of New Caledonia’s largest island, Grande Terre, between 0 UTC and 12 UTC Saturday. Heavy damage is likely on the island, and Niran’s eyewall will pass perilously close to the capital city of Noumea (population 95,000).
Earlier this week, Niran brought heavy rains and high winds to Australia’s Queensland state, causing damage to the banana crop estimated at $138 million. Niran did not make landfall in Australia.
South Pacific Ocean tropical cyclone history
NOAA’s hurricane history database lists 14 other tropical cyclones in the South Pacific Ocean that have achieved category 5 strength since 1988; accurate satellite data in the region dates to about 1990. The most recent Cat 5, Tropical Cyclone Harold in April 2020, caused widespread destruction in the Solomon Islands, Vanuatu, Fiji, and Tonga, killing 30 and causing more than $120 million in damage.
Three tropical cyclones are tied for being the most powerful storms on record in the South Pacific (all with 180 mph winds): Tropical Cyclone Winston (2016), Tropical Cyclone Zoe (2002), and Tropical Cyclone Monica (2006). Monica (in Australia) and Winston (in Fiji) both made landfall while at category 5 strength.
Niran is Earth’s second category 5 storm of 2021, the other being Tropical Cyclone Faraji, which reached category 5 strength on February 8 in the South Indian Ocean. It is uncommon to have two Southern Hemisphere Cat 5s so early in the year; the last time this occurred was in 2015, when Tropical Cyclone Eunice became the Southern Hemisphere’s second Cat 5 on January 30. There are only two years on record when the Southern Hemisphere has recorded as many as three category 5 storms: 2015 and 2003.
Earth averaged 5.3 category 5 storms per year between 1990 and 2020, according to ratings made by NOAA’s National Hurricane Center and the U.S. Navy’s Joint Typhoon Warning Center. The quality of the Cat 5 database is too poor and the time series of decent data on these storms too short to make definitive conclusions about how climate change may be affecting these most fearsome of storms. However, climate change is expected to make category 5 storms stronger and more numerous in coming decades.