These storms may be a harbinger of increasingly severe tropical cyclones in future decades as the Earth continues warming.
The most recent vicious storm, Tropical Cyclone Fantala, attained peak winds of 173 mph north of Madagascar this past weekend. According to meteorologist Bob Henson at Weather Underground, it became the most intense tropical cyclone on record in the Indian Ocean. Fantala has since lost some steam and is forecast to weaken to a tropical storm over the southern Indian Ocean by early next week. Fortunately, it has avoided any land areas.
[Update, April 21: Capital Weather Gang contributor Phil Klotzbach points out the intensity of Tropical Cyclone Agnielle in 1996 was comparable to Fantala, meaning it is likely tied for the strongest on record.]
Just two months before Fantala, Tropical Cyclone Winston became the fiercest storm on record in the South Pacific, with peak winds of 185 mph. This storm devastated parts of Fiji.
And four months before Winston, Hurricane Patricia (October 2015) became the strongest storm measured to date by the National Hurricane Center in the Northeast Pacific. Its peak winds reached 215 mph before it slammed into Mexico’s west coast.
Patricia was just one of 25 Category 4 or 5 tropical cyclones in 2015 in the Northern Hemisphere, the most on record by far.
This is not to mention November 2013’s Super Typhoon Haiyan, which became the strongest tropical cyclone in the northwest Pacific (and the Eastern Hemisphere) based on wind speed. Its 195 mph maximum sustained winds devastated parts of the Philippines.
To be sure, because the intensity of these storms was not observed by aircraft, except for Patricia, there is some uncertainty in their exact measurements. And, the period of record in the Indian Ocean, where Fantala developed, only dates to 1990.
But all of these storms formed in areas where ocean temperatures were much warmer than normal and during an era in which ocean temperatures are warming.
The recent ocean heating provided by El Niño, particularly in the Pacific, has certainly played a role in this flare-up of intense storms. But the longer-term ocean warming trend, related to growing concentrations of greenhouse gases in the atmosphere, is very likely to be playing an important role as well.
Published studies have documented an increase in the intensity of the strongest storms in several ocean basins in recent decades, although an unambiguous global warming signal in tropical cyclone activity hasn’t emerged. Such a signal is expected to become clearer in the future.
A NOAA-led study published in September projects increases in “the number and occurrence days of very intense category 4 and 5 storms” by the end of the century, and, more generally, NOAA projects an increase in the average intensity of tropical cyclones.
Fantala, Winston, Patricia and Haiyan may portend more frequent and intense severe tropical cyclones, especially during El Niño episodes in the Pacific (in the Atlantic, more intense storms would occur during La Niñas).