Physical Address
23,24,25 & 26, 2nd Floor, Software Technology Park India, Opp: Garware Stadium,MIDC, Chikalthana, Aurangabad, Maharashtra – 431001 India
Sri Lanka has faced the devastating tropical cyclone “Ditwah” and lost hundreds of lives. There has been a lot of social media content about the issue, and many such posts are misleading the public. In the claim below, we are extracting the core of one such social media post that is viral. Here’s the post:
Claim Post: Facebook
Claim: Tropical cyclones require the Coriolis effect related to Earth’s rotation to spin, so they “can’t form” near the equator between 0°–5°, where Coriolis is weak. Warming sea-surface temperatures (SST) in the tropical Indian Ocean, now between 30–31.5 °C, supposedly boost cyclogenesis even near the equator. This explains rare storms, Ditwah, Senyar, and Koto, forming at low latitudes, and predicts that such equatorial cyclones will become more frequent with higher SST, shifting winds, etc.
Fact: Misleading. It is true that cyclones need Coriolis spin and rarely form right at the equator, but warm waters alone cannot “create” the needed spin or change that fact. Tropical SSTs are indeed very warm, often ≥28 °C and have risen, but these temperatures exceed the 26.5 °C cyclogenesis threshold even historically, so warming by itself does not explain new equatorial storms. There is no clear evidence that equatorial cyclones are now regularly increasing in frequency; they remain rare anomalies. However, as the world’s oceans and atmosphere warm at an accelerating rate due to the rise in greenhouse gases from burning fossil fuels, tropical cyclones are expected to become more intense. This is because cyclones get their energy from warm oceans. The warmer the ocean, the more fuel for the storm.
What We Found
Tropical cyclones draw energy from warm ocean water and require a rotating low-pressure system. However, the Coriolis force, which occurs due to Earth’s rotation, is essentially zero at the equator and only becomes strong enough a few hundred kilometres north or south of it. Meteorologists note “cyclones rarely form within 5° of the equator” because there’s “not enough Coriolis force” to spin them up. In fact, virtually all recorded cyclones originate well away from 0°–5° latitude. Warm water fuels cyclones, but it does not generate rotation. A higher SST does not increase the Earth’s Coriolis force – that depends only on latitude. Thus, the claim that rising SST “makes the Coriolis stronger” or alone enables equatorial cyclones is false. In other words, no matter how warm the sea gets, without sufficient Coriolis effect, a storm cannot develop the classic cyclone structure near 0°.
At the same time, tropical waters are indeed very warm. The Indian Ocean has warmed faster than other basins, and researchers report parts of the tropical Indian Ocean already reaching 30–32 °C in recent years. For comparison, 26.5 °C is widely cited as the rough minimum for cyclones to form. However, even before current warming, equatorial seas generally exceeded that threshold year-round – so warm water alone was not the limiting factor. Warming oceans do “give more fuel” to storms, while cyclones “get their energy from warm oceans” and can intensify rainfall, but by themselves, they cannot make up for the lack of spin at the equator. In summary, yes, SSTs of ~30 °C exist, and that allows cyclones where Coriolis is sufficient, but it isn’t the “new reason” cyclones suddenly form right at the equator.
The few recent equatorial storms like Cyclone Vamei in 2001 at ~1.4°N, or Cyclone Senyar at ~3.8°N in 2025, remain exceptional. There is no demonstrated trend of frequent cyclone genesis exactly at 0–5° latitude. In fact, a recent study of the North Indian Ocean found that mid-latitude cyclones have actually become more common relative to low-latitude storms: between 1951–1980 and 1981–2010, the number of cyclones originating between 5°–11° N declined by about 43%. That decline was attributed largely to natural variabilities like Pacific Decadal Oscillation, wind shear, etc, and not warming SST. Climate models do not project a blanket rise in low-latitude cyclones simply due to warming; on the contrary, many projections suggest fewer total cyclones globally but with higher average intensity as the climate warms. Scientists emphasise that the recent rare equatorial cyclones in Asia were driven by unusual weather patterns like active convergence zones and equatorial waves as much as by warm water. Warming seas likely helped those storms carry more moisture, as noted by IPCC author Roxy Koll: “warmer oceans supply more moisture to the atmosphere and a warmer atmosphere holds more moisture for a longer time – the result is short bursts of heavy rains from monsoons and cyclones”, but they did not create the missing Coriolis spin.
What does the future hold?
Climate change may allow very rapid intensification of any storm that does form, and shift some cyclone tracks, but it will not magically remove the physics that inhibit equatorial storms. Experts say any increase in equatorial cyclone frequency would require a combination of warming and favourable large-scale patterns like a positive phase of the Pacific Decadal Oscillation – and even then, such storms would remain extremely rare. Thus, claims that climate change will make cyclones routine in Sri Lanka or right at 0°–5° are not supported by current evidence. It is true, however, that intense cyclones in the region can bring more rain when SSTs are warmer. So while Sri Lanka and nearby countries may see heavier flooding from each storm, the frequency of cyclones originating exactly on the equator is not expected to suddenly jump simply due to higher sea temperatures, but the intensity of the cyclones will be high.
References
https://www.aoml.noaa.gov/hrd-faq
https://en.wikipedia.org/wiki/Tropical_cyclone
Why the Indian Ocean is spawning strong and deadly tropical cyclones
Banner image: Photo by Lucy Chian on Unsplash
Copyedited by Vivek Saini
