Satellite images capture twin Cyclonic Storm over the Indian Ocean

Monday, May 09: Last week, as a cyclonic circulation started to take shape near the Andaman Sea, meteorologists began to warn the potential impacts on the eastern coast of India. On Sunday, the system intensified into a Severe Cyclonic Storm! Still, the threat to the coast appears minimal as it is expected to weaken into a deep depression by Wednesday while recurving along and off the Odisha coast.

Meanwhile, its twin has emerged over the southern parts of the Indian Ocean over the weekend. The storm has been named Cyclone Karim, based on the suggestion from the East African country Seychelles. The cyclone is currently a category two hurricane with a wind speed of 112 kmph gusting at nearly 140 kmph.

On the other hand, Cyclone Asani has remained a Severe Cyclonic Storm on Monday with wind speeds of 100-110 kmph gusting to 120 kmph, as per the India Meteorological Department (IMD). It lies roughly 500 km southeast of Visakhapatnam in Andhra Pradesh and is expected to move towards the Odisha coast by Tuesday. By Wednesday, it will recurve and move along the Odisha coast while weakening into a cyclonic storm.

Twin tropical cyclones spinning in opposite directions north and south of the equator are not new!

Cyclone Fani formed over the Bay of Bengal in April 2019 along with Tropical Cyclone Lorna over the southern Indian Ocean. While Fani turned into an extremely severe cyclonic storm with a maximum wind speed of 250 kmph, Lorna was a Category 1 hurricane and could attain a maximum of 70 kmph.

Such twin tropical cyclones resemble mirror images of each other, spinning at roughly the same longitude but in opposite directions, as seen in the satellite images. Such events are also common in the western Pacific Ocean. They don't happen in the eastern Pacific or Atlantic Basins because tropical cyclones do not occur in lower latitudes south of the equator there.

Winds around low-pressure systems spin clockwise in the Southern Hemisphere but counterclockwise in the Northern Hemisphere due to the Coriolis effect a force caused by Earth's rotation that deflects winds to the left in the Southern Hemisphere and to the right in the Northern Hemisphere.

Similar to 2019, the instigator of this pair of cyclones was the Madden-Julian Oscillation (MJO), a disturbance near the tropics that moves east around the globe every 30 to 50 days. Westerly winds over the equator line on the Indian Ocean have been strong past several days, likely due to MJO. Such strong westerly winds over the equator line can sometimes induce cyclonic circulations and lead to the simultaneous formation of cyclones over the Northern hemisphere and Southern hemisphere, called Twin Cyclones.

"We usually see the twin cyclones develop following the passage of the convectively-active phase of the MJO," explains Dr Michael Ventrice, an atmospheric scientist at The Weather Company, an IBM Business. Ventrice said the MJO primes the environment for tropical cyclone development thanks to large gyres of low-pressure left behind from enhanced thunderstorms near the equator and enhanced areas of spin north and south of the equator from low-level westerly winds.

When these twin storms are close to each other, i.e., within 1000 km, they even interact with each other. However, Asani and Karim are unlikely to interact because the distance between them is more than 2800 km.

The Indian Ocean has a year-round Cyclone Season. The tropical cyclone season in the northern Indian Ocean, which includes the Bay of Bengal and the Arabian Sea, is quite unusual, with two peaks one from April to June and the second from September to December. However, the cyclone season over the southwest Indian Ocean basin peaks between November and April, making Karim quite an exception.

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Twin Cyclones Asani and Karim Form Over Indian Ocean; Satellite Images Capture Twins on Opposite Sides of Equator | The Weather Channel - Articles...