Tropical Cyclone Ambali on Thursday morning as a tropical storm, left, and 24 hours later on Friday morning as a Category 5-equivalent cyclone, right. (CIRA/RAMMB/EUMetSat)

On Thursday morning, Tropical Cyclone Ambali was named in the Indian Ocean, with an intensity equivalent to a tropical storm. By Friday morning local time, it had transformed into a borderline Category 5 behemoth. The cyclone’s extremely rapid intensification rate is likely to beat out anything ever observed in the Southern Hemisphere, where satellites monitor such storms, while claiming the second-place spot globally for a storm’s 24-hour strengthening rate.

It’s part of an ominous trend of recent storms that bears a strong climate connection, according to scientific studies.

Fortunately, the storm hit its apex far from land, and it is forecast to continue to roam across the open ocean while weakening. Cyclone Ambali weakened significantly overnight and is now equivalent to a Category 2 storm. It’s forecast to drift harmlessly over the Arabian Sea, passing well east of Madagascar and staying north of Mauritius.


The Joint Typhoon Warning Center is forecasting Ambali to pass well north of Mauritius as it weakens at sea. (JTWC)

Though the storm won’t impact land, it’s grabbing headlines and captivating meteorologists alike, thanks to its unprecedented bout of extremely rapid intensification.

All told, the storm’s satellite-estimated wind speeds increased by 115 mph in 24 hours. (While the storm hit Category 5 intensity based on satellite estimates in between official storm advisories, the Joint Typhoon Warning Center did not classify it officially as a Cat. 5, instead stopping just shy, at 155 mph.)

According to Colorado State University hurricane researcher Philip Klotzbach, that’s the greatest 24-hour intensification of any Southern Hemisphere tropical cyclone on record. Globally, only one storm has ever surpassed that benchmark: Hurricane Patricia, which exploded off the Pacific coast of Mexico in 2015. That storm — the strongest tropical cyclone ever recorded worldwide based on wind speed — at one point raged over the open ocean with sustained 215 mph winds.

Contributing to Ambali’s rapid intensification were plentiful warm ocean waters and calm upper-level winds. These conditions allowed the storm to develop free of perturbations or interruptions.

Technically speaking, rapid intensification requires that a storm’s core wind speeds increase by at least 35 mph in 24 hours. Tropical Cyclone Ambali intensified at 330 percent of that rate. It’s reminiscent of Hagibis, a West Pacific super typhoon with an intensity that jumped 90 mph in 18 hours in October. That storm went on to cause damage in Japan, where it hit with 100 mph winds and rainfall totals topping three feet.

Hagibis technically intensified about 4 percent faster than Ambali but didn’t keep that streak up for the full 24 hours.

In recent years, several storms in the Atlantic Basin have undergone rapid intensification, blossoming into beasts that proved highly damaging. Among them were hurricanes Matthew, Harvey, Irma, Maria, Florence and Michael — all of which were once-major hurricanes that struck or clipped the United States in the past few years. Both of this season’s Atlantic Category 5′s, including Hurricanes Dorian and Lorenzo, rapidly intensified, too. Hurricane Dorian struck the northwest Bahamas as a Category 5 storm.

The climate change tie

If it seems to you as though rapid intensification is happening with virtually every major storm these days, you’re not alone. Scientists have shown this trend is probably connected to climate change.

Kerry Emanuel, a professor at the Massachusetts Institute of Technology, has warned that climate change is likely to dramatically increase the frequency of rapid intensification.

“We would expect a significant increase in extremes of storm intensification, including those that happen just before landfall,” Emanuel wrote in a 2017 study published by the American Meteorological Society. He also noted that storms intensifying 115 mph or more before landfall — which is roughly a once-a-century occurrence nowadays — could happen every 5 or 10 years on average by the end of the century.

“The incidence of storms that intensify rapidly just before landfall could increase substantially by the end of this century,” Emanuel wrote. “And as rapid intensification is difficult to forecast, there is a risk of an increased frequency of poorly anticipated, high-intensity landfalls, leading to higher rates of injury and death.”

One example of a storm that rapidly intensified straight through landfall was Hurricane Michael, which devastated portions of the Florida Panhandle last year.

In another study, a team of atmospheric scientists found that “climate change could allow [tropical cyclones] to rapidly intensify over a larger portion of the world’s oceans and increase [tropical cyclone] intensification rates dramatically.”

The Indian Ocean has been cranking out storms this season. The North Indian Ocean has churned out five times more energy in storms this season compared with the average, including a record high number of “very severe cyclonic storms.” Before it was eclipsed by Cyclone Ambali, Category 4 Cyclone Kyarr became the Arabian Sea’s strongest cyclone in 12 years at the end of October.


The Indian Ocean is ripping with storms, as three cyclones spin simultaneously while a fourth area of disturbed weather looms to the northeast. (CIRA/RAMMB/EUMetSat)

Ambali is rotating clockwise, spinning up in the South Indian Ocean on the other side of the equator. The season on that side of the planet has featured only one other system so far — Category 1 equivalent Cyclone Belna — which is ongoing now.

Across the entire Indian Ocean, the basin is packed. Three tropical cyclones are whirling, with a fourth system at its early stages of development.

Clarification: An earlier version of this article stated the storm reached Category 5 intensity. Satellite imagery suggested Category 5 intensity, but the Joint Typhoon Warning Center classified it just shy of Category 5 status, with maximum sustained winds of 155 mph.