Cyclone Aila kills at least 120 in India, Bangaldesh; 91L forms

The year's deadliest tropical cyclone so far, Tropical Cyclone Aila, hit the India/Bangladesh border region on May 25 as a borderline tropical storm/Category 1 hurricane. Aila brought sustained winds of 65 - 75 mph at landfall, and a 3 - 4 meter (10 - 13 foot) storm surge to coast of eastern India and western Bangladesh. Approximately 150,000 were left homeless In India, and at least 45 people were killed, many of them in the Kolkata (Calcutta) area. Damage was heavy in the city, which is India's second largest, with a population of 7.8 million. In Bangladesh, at least 89 are dead and ten of thousands homeless. The death toll will likely go higher, as over 100 people are missing in Bangladesh. The Bay of Bengal is no stranger to deadly cyclones--fifteen of the world's twenty deadliest tropical cyclones have been Bay of Bengal storms that have hit Bangladesh, India, or Myanmar. The most recent was last year's Cyclone Nargis, which killed 146,000 people in Myanmar.


Figure 1. Satellite image of Aila as it made landfall near the India/Bangladesh border. Image credit: Navy Research Lab, Monterey.

Aila began as a "monsoon depression"--a large cyclonic disturbance that formed within the advancing Southwest Monsoon. The monsoon depression filled the entire Bay of Bengal, then gradually intensified between May 23 and 25 to the threshold of Category 1 hurricane strength. Since Aila started as a monsoon depression, it was a huge storm, with an eye over 100 miles in diameter. The storm helped pull the welcome rains of the Southwest Monsoon into India and Bangladesh a week ahead of normal (Figure 2). For reasons we don't fully understand, tropical cyclones in the North Indian Ocean are very predictable using computer models. Dr. Peter Webster of Georgia Tech was predicting the formation of Aila ten days in advance.


Figure 2. Progress of the Southwest Monsoon over India this week was aided by Cyclone Aila. Image credit: India Meteorology Department.

Disturbance 91L forms near North Carolina
An area of disturbed weather, dubbed "91L" by the National Hurricane Center, has formed a few hundred miles southeast of North Carolina. The disturbance is over waters of 25 - 26°C and has wind shear of 10 - 15 knots over it, and these conditions are marginally favorable for some slow development to occur over the next 24 - 36 hours. The disturbance will track northwards towards North Carolina's Outer Banks over the next 24 - 36 hours, then get swept northeastwards out to sea. It is unlikely that the disturbance has enough time to develop into a tropical depression. However, the storm should bring winds of 20 - 25 mph and heavy rain to North Carolina's Cape Hatteras on Wednesday. An Air Force hurricane hunter flight is on call to investigate the system on Wednesday afternoon.

Jeff Masters