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An area of unsettled weather has developed into Cyclonic Storm Mocha over the southern Bay of Bengal. Meteorologists have been eagerly watching the system, which could make landfall near the Myanmar-Bangladesh border region in the coming days.
Mocha’s outer cloud bands are a vast system, spanning nearly the entire width of the great bay in the northeastern Indian Ocean, about 1,000 miles (1,600 km) wide. The cyclone was only in its early stages on Thursday with sustained winds of about 60 mph and increasing strength, but is expected to quickly develop into a very severe cyclone storm if it heads north this weekend or early next week and northeast toward land.
It was intended to make landfall as a great tropical cyclone, potentially causing disaster.
The current landfall zone is likely to be concentrated in northern Myanmar, also known as Burma, near the border with Bangladesh. This is a region known for tropical cyclone mega-disasters – with extraordinary storm surges hitting densely populated areas – and currently at war.
Mocha was analyzed Thursday with sustained winds of around 58 mph (50 knots) as the main strengthening phase began.
Sitting over waters of about 86 degrees (30 degrees Celsius) or higher, more than warm enough to weather a violent storm, Mocha was already generating waves up to 25 feet high and counting.
“Mocha will continue to move northeast for the remainder of the forecast,” the Joint Typhoon Warning Center (JTWC) wrote in its Thursday update. They say the landing is likely to occur “south of the Bangladesh-Myanmar border this weekend.”
With minimal wind shear — disruptive gusts in the air that can impede development — Mocha is expected to develop into a severe cyclone, locally labeled a severe cyclone, over the next 12 to 24 hours, with another and potentially rapid one reinforcement afterwards.
Official forecasts Indian Meteorological Department and the Joint Typhoon Warning Center are projecting the storm to maintain a sustained speed of at least 100 to 115 miles per hour (85 to 100 knots) on landfall. Given the favorable environment of warm waters, minimal disturbing shear, and relatively slow motion, it is very likely that these solutions are rather conservative.
As is often the case with tropical cyclones, Mocha’s trail is safer than its intensity. As the storm moves along the periphery of a powerful high-pressure dome, any shifts in landfall should be minor. Intensity factors are much more difficult to determine.
Some of the best tropical cyclone weather models suggest that a much stronger storm than officially forecast is likely as it nears the coast. For example, recent results from the HWRF hurricane model have shown that peak pressure drops to almost 900 millibars, which would easily correspond to a Category 4 or 5 intensity.
Even if Mocha peaked above the water and then weakened on its way to shore, effects such as deadly storm surges and crashing waves and torrential flooding rains would already be seared in.
People near the landfall and in low-lying areas throughout the region should complete their preparations or conduct evacuations as needed. More than 10,000 people have already sought shelter, according to Myanmar Now.
A tragic cyclone story and an ongoing war
The region is notorious for major storm surges, which are sea level rises when a storm passes. A recent article by an expert puts it in a nutshell.
“The Bay of Bengal hosts only 4% of all tropical cyclones worldwide,” wrote Roxy Mathew Koll, climate scientist at the Indian Institute of Tropical Meteorology. “[B]But more than 80% of hurricane fatalities come from this region.”
The main reasons for such a high toll are socio-economic in nature and in particular the high population density in the northern bay. However, the water is also typically very warm, which favors rapid intensification. Climate change is only adding fuel to the fire.
It doesn’t appear to be running in real time yet, but EMC is running HAFS (the HAFS-A version). #Mocha. Last night’s forecast showed a strong Category 4 cyclone making landfall in Myanmar. I hope the preparations there are in full swing. pic.twitter.com/2TVyb0qZMI
— Andy Hazelton (@AndyHazelton) May 11, 2023
Then there is the simple geography of the bay.
The bay is wide in the south, where storms enter, and converging at a point in the north, allowing storm surges to be amplified by the channeling water. The sea-to-land gradient is also quite small, with a large regular tidal range amidst large river deltas. All factors favor large storm surges inland.
The bay has a long history of severe storms. Amphan in 2020 was the most recent of these super-catastrophes. It landed in the northern bay after achieving Category 5 status. In 2017, a Category 1 Mora stranded near the Bangladesh-Myanmar border, killing more than 150 people.
In May 2008, Cyclone Nargis became the second-deadliest tropical cyclone of all time and the deadliest in Myanmar. More than 135,000 people are believed to have been killed, with most of the deaths taking place in this country.
Another factor in this case is the ongoing civil war in Myanmar. With nearly two million internally displaced people and another million refugees, large populations could be at additional risk. The landing region south of the Bangladesh border has been an active site of fighting in the past and there are several huge camps for displaced people in the area.