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Article | WTW Research Network Newsletter

An unusually large number of Category 5 tropical cyclones

By Cameron Rye | July 20, 2023

With so many extreme weather events in the first half of the year, it was easy to have overlooked the unusual tropical cyclone activity that produced five Category 5 storms in five months.
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Category 5 equivalent[1] tropical cyclones are rare, with an average of 4.7 occurring per year since 1980, accounting for less than 10% of all tropical cyclones globally (Figure 1). However, this year has been unusual, with five events in the first five months: Freddy, Kevin, Isla, Mocha, and Mawar (Table 1). In comparison, an average of 1.1 events have occurred globally between January and May since 1980. The only recent precedent is 2015, when six Category 5 storms had developed by the end of May.

This year's events have also broken a number of individual records (Table 1). Very Intense Tropical Cyclone Freddy produced an Accumulated Cyclone Energy (ACE) of 87 – the highest for a tropical cyclone on record. At 35 days, Freddy may also have broken the record for the longest-lived cyclone, although the World Meteorological Organisation (WMO) is still verifying this. The storm's power caused significant damage when it made landfall in Madagascar and Mozambique, resulting in nearly 1,450 fatalities, making it the third deadliest on record in the Southern Hemisphere.

Category 5 equivalent tropical cyclones Jan-May 2023

Table 1: Category 5 equivalent tropical cyclones Jan-May 2023
Name Regions Affected Genesis Date Wind Speed (mph)* Record Broken
Freddy Madagascar, Mozambique 5 February 165 Highest-ACE-producing tropical cyclone ever recorded
Kevin Solomon Island, Vanuatu 26th February 160 -
Ilsa Western Australia 6 April 160 Strongest 10-minute sustained windspeed at landfall in Australia
Mocha Myanmar, Bangladesh 8 May 175 Joint highest 1-minute sustained windspeed in the North Indian Ocean
Mawar Guam, Philippines, Taiwan, Japan 17 May 185 Highest ACE and joint highest 1-minute sustained windspeed in May

*1-minute sustained wind speed

Severe Tropical Cyclone Ilsa made landfall in Western Australia in April as a Category 5 storm northeast of Port Hedland. On Bedout Island, a 10-minute sustained wind speed of 136mph was measured, breaking the previous Australian record for a landfalling storm set by Cyclone George in 2007. Because the storm avoided populated areas, including the world's largest iron ore export hub in Port Headland, economic and insurance losses were minimal.

In early May, Extremely Severe Cyclonic Storm Mocha became the North Indian Ocean's joint strongest tropical cyclone, with a 1-minute sustained wind speed of 175 mph. The cyclone made landfall in Myanmar, about ten miles northwest of Sittwe, the regional capital of Rakhine state. Given the storm's proximity to the world's largest refugee camp in Cox's Bazar, Bangladesh, there were fears of significant casualties prior to landfall. However, authorities and aid organizations were able to evacuate hundreds of thousands of people in Myanmar and Bangladesh ahead of the event, mitigating the humanitarian impact.

A few weeks later, Super Typhoon Mawar became the most powerful storm of 2023 so far, with sustained 1-minute winds of 185 mph. The cyclone broke two records: the highest ACE and the joint-highest 1-minute sustained windspeed observed in the month of May. The only other storm to reach 185 mph in May is Typhoon Phyillis in 1958. Mawar passed north of Guam, bringing heavy rain and strong winds to the island, making it the strongest typhoon to affect the U.S. territory in over two decades.

Freddy and Mocha highlighted that there is still a considerable protection gap in many tropical cyclone-prone countries, with economic losses far exceeding insurance coverage. By providing pre- determined and faster pay-outs to fund emergency response and speed up recovery, parametric (or index-based) insurance is seen as one option for improving resilience to the impacts of these types of events. For example, WTW recently designed a parametric insurance product for UNICEF's Today and Tomorrow Initiative, which was funded by the governments of the United Kingdom and Germany.

The parametric index combines tropical storm wind speeds modelled by Kinetic Analysis Corporation, with child population distribution to capture impacts on vulnerable populations. The program covers children and families in eight UNICEF host countries that are vulnerable to tropical cyclones: Bangladesh, Comoros, Haiti, Fiji, Madagascar, Mozambique, Solomon Islands, and Vanuatu.

Scientists will most likely need some time to dissect the reasons for the increase in early-season activity this year. Global sea surface temperatures in the first half of 2023 have been at all-time highs since satellite records began[2], which may have played a role. But for now, all eyes will be on the upcoming North Atlantic (Section 3.2) and Western Pacific seasons to see if the trend continues. The largest number of Category 5 storms ever recorded in a calendar year is 12 in 1997, so there is still some way to go to break this record.

Footnotes

  1. Defined as sustained 1-minute wind speeds greater than or equal to 157 mph according to the Saffir-Simpson scale. Return to article
  2. Climate Reanalyzer. University of Maine. Daily Sea Surface Temperature (2023) Return to article

Disclaimer

All statistics were correct at time of publishing.

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