A WMO international committee of experts working under the auspices of the Weather and Climate Extremes Archive conducted a detailed analysis and verification of the distance and duration. The evaluation committee recognized Tropical Cyclone (TC) Freddy’s duration of 36.0 days at tropical storm status or higher as the new world record for the longest tropical cyclone duration. 

A reanalysis of the duration of the previous record holder TC John in the North Pacific Ocean in 1994 indicated that it existed at tropical storm status or higher for a combined duration of 714 hours, or 29.75 days.

In terms of distance, the WMO analysis indicated that TC Freddy travelled 12 785 km ± 10 km (7 945 miles, 6 905 nautical miles) at tropical storm status or above. This is a close second to TC John, which covered 13 159 km ± 10 km (8 177 miles, 7 105 nautical miles) at tropical storm status or above. To put that number in perspective, that distance is nearly 33% of the Earth’s circumference. 

“Freddy was a remarkable tropical cyclone, not only for its longevity but also for its ability to survive multiple land interactions, which unfortunately had significant consequences for southeast African populations," says Chris Velden, committee member and tropical cyclone/satellite expert from the University of Wisconsin, USA. 

“This investigation highlights the meticulous care that the WMO undertakes in certifying all weather observations. Such painstaking evaluation provides the critical confidence that our global records of all weather phenomena are properly measured,” said Randall Cerveny, Rapporteur of Climate and Weather Extremes for WMO.

WMO will update its Archive of Weather and Climate Extremes to reflect the new record. The archive includes the world’s highest and lowest temperatures, rainfall, heaviest hailstone, longest dry period, maximum gust of wind, longest lightning flash and weather-related mortalities. It is used by weather historians and, increasingly, by policy makers. 

“The extremes presented for adjudication for the WMO Weather and Climate Extremes Archive are ‘snapshots’ of our current climate. It is possible, and indeed likely, that greater extremes will occur in the future. When such observations are made, new WMO evaluation committees will be formed to adjudicate these observations,” said Randall Cerveny.

The WMO evaluation committee consisted of experts from the Tropical Cyclone Warning Center Melbourne (Bureau of Meteorology, Australia), the Regional Specialized Meteorological Centre (RSMC) La Réunion (Météo-France, France) that forecasted TC Freddy, as well as scientists from Spain, Canada, Hong Kong China, and the United States

The findings were published in the online Bulletin of the American Meteorological Society.