Tropical Cyclone Roanu a Flood Threat in Eastern India, Bangladesh, Myanmar

Jon Erdman
Published: May 20,2016
Tropical Cyclone Roanu may not become an intense Bay of Bengal cyclone, but it is likely to produce dangerous flooding in parts of eastern India, Bangladesh, and Myanmar into the weekend.
After dumping over a foot of rain, triggering destructive mudslides in Sri Lanka earlier in the week, an area of low pressure consolidated enough convection near its center to be deemed a tropical cyclone just off the coast of India's Andhra Pradesh state northeast of the city of Chennai Wednesday.
(MORE: Where Hurricane Season Peaks Twice)
Convection burst near the center of Roanu early Friday as its center meandered near the eastern coast of India, spreading heavy rain through parts of Andhra Pradesh, Odisha, and West Bengal states.

Current Status: Tropical Cyclone Roanu

Despite the convective burst, thanks to wind shear, the change in wind speed and/or direction with height, Roanu is not expected to strengthen much as it tracks generally northeast toward the coast of Bangladesh Saturday, then inland into northern Myanmar as a remnant low.

Tropical Cyclone Roanu Forecast Path

As a result, the primary threat from Roanu will be heavy rainfall.
Friday, several locations along the eastern India coast and southern Bangladesh picked up at least 120 millimeters of rain (about 4.72 inches).
Kalingapatam, India tallied almost 9 inches of rain (227 millimeters) Friday alone.
In general, the rainfall potential of a tropical cyclone is not a function of its intensity (i.e. maximum sustained winds), but rather its forward speed.
Some of the most extreme rainfall events worldwide have occurred when tropical cyclones, in some cases as weak as depressions or even remnant lows, move slowly, or stall.
(ONE EXAMPLE: "Allison" 2001 in Houston)
Roanu will move slow enough to dump some rather prolific rainfall, particularly over central and eastern Bangladesh, Myanmar, and the eastern states of India.

Forecast Additional Rainfall Through Monday

Moist southerly winds ahead of the center of Roanu will also steer clusters of thunderstorms with heavy rain ashore in these same areas.
This poses a dangerous threat of flooding and landslides, particularly in the higher terrain of the eastern India states, far north and western Myanmar, even perhaps into extreme south-central China into next week.
(FORECAST: Kolkata | Dhaka | Chittagong)
Last summer, Tropical Cyclone Komen combined with the normal wet phase of the Asian monsoon to dump over 3 feet (1 meter) of rain to parts of eastern Bangladesh.
The resulting flooding and mudslides claimed at least 200 lives and destroyed 55,000 homes.
Fortunately, Roanu is not expected to intensify appreciably. The Bay of Bengal has a notorious history for the world's deadliest tropical cyclones, owing to both population density of low-lying areas near the coast and the shallow northern end of the Bay of Bengal, funneling storm surge into Bangladesh, in particular.
(MORE: The Storm That Killed 300,000)
In early May 2008, Cyclone Nargis slammed into southern Myanmar, driving a storm surge into the country's Irrawaddy Delta, claiming over 138,000 lives in the country's worst natural disaster.

MORE: Cyclone Phailin Hits India (October 2013)