Cyclonic Storm Roanu was a relatively weak tropical cyclone that caused severe flooding in Sri Lanka and Bangladesh during May 2016. It was the first tropical cyclone of the annual cyclone season. Roanu originated from a low-pressure area that formed south of Sri Lanka, gradually drifted north and intensified into a cyclonic storm on 19 May. However, wind shear and land interaction caused it to weaken slightly, before reintensifying as it accelerated towards the coast of Bangladesh.
The storm was responsible for 105 deaths in Sri Lanka and another 30 deaths in Bangladesh. A further 99 persons in Sri Lanka were reported missing. Damage throughout Sri Lanka reached US$2 billion. Roanu also brought torrential rainfall to the Indian states of Tamil Nadu, Andhra Pradesh, Kerala and Odisha as it drifted in a generally northeastward direction, close to the coast.
Meteorological history
Under the influence of a trough, a low-pressure area formed over the Bay of Bengal on 14 May. It slowly consolidated as it paralleled the east coast of Sri Lanka, prompting the India Meteorological Department (IMD) to classify it as a depression on 17 May. Late the same day, the Joint Typhoon Warning Center (JTWC) issued a Tropical Cyclone Formation Alert (TCFA), soon after which the JTWC upgraded the system to a tropical storm. Simultaneously, the IMD upgraded the storm to a Deep Depression, prompting the issuance of cyclone warnings for the states of Andhra Pradesh and Odisha. On 19 May, the IMD reported that the storm had reached cyclonic storm intensity, and assigned it the name Roanu.
At the time, Roanu was tracking slowly northward along the northern periphery of a subtropical ridge located over the Malay Peninsula. Despite favorable outflow and warm sea surface temperatures (SSTs) reaching 31 °C (88 °F), its proximity to land and moderate vertical wind shear kept the storm from intensifying rapidly. The diurnal temperature variation over land and the persistent wind shear began to affect the deep convection obscuring the low-level circulation center (LLCC). In the late hours of that day, Roanu showed a weakening trend after most of the convection covering the LLCC was sheared off. During that time, Roanu was located approximately 150 kilometres (93 mi) from Visakhapatnam. However, the wind shear soon decreased, and the storm reestablished deep convection over and around the LLCC, forming a central dense overcast in a period of 6 hours. SSMIS imagery revealed tightly curved rainbands wrapped into the LLCC. As a result, Roanu re-intensified as it accelerated east-northeastwards towards the coast of Bangladesh, and reached its peak intensity with winds of 85 km/h (55 mph) and a minimum central pressure of 983 hPa (mbar; 29.03 inHg). On 21 May, Roanu made landfall just northwest of Chittagong, Bangladesh. Continuing to accelerate inland, Roanu steadily weakened and degenerated into a remnant low on the next day.
Preparations
Preparations for the storm began even before the IMD started tracking it as a depression. As the area of low pressure tracked closer to the country, the Meteorology Department of Sri Lanka issued a warning on 13 May stating that the disturbance would affect the country. Fishermen were advised to be vigilant. On 14 May 2016 the Meteorology Department issued a severe weather advisory for twelve hours commencing 11:30 IST. Up to 100mm of rain was expected in parts of eastern and southern Sri Lanka with wind speeds up to 70-80 kmh at sea. Later, The National Building Research Organisation (NBRO) issued landslide warning in the districts of Badulla, Monaragala, Kandy, Ratnapura, Kurunegala, Nuwara Eliya, Kegalle and Matale. President Maithripala Sirisena instructed the local authorities to provide relief to those affected by the system. The Minister Of Disaster Management, Defense Secretary, Tri Forces' Commanders and the Inspector General Of Police were instructed to undertake the operation. The Road Development Authority waived Tolls on the Southern Expressway between Kottawa to Kadawatha due to the weather. Schools in Central Province, North Western Province, Sabaragamuwa Province and Western Province are closed due to the floods. As water levels on the Kelani River rose rapidly, the DMC warned those living near its banks to move to safety. The Ceylon Electricity Board imposed emergency power cuts on the Colombo suburbs of Kohilawatte, Kolonnawa, Kotikawatte, Orugodawatta, Sedawatta, Sinhapura and Wellampitiya as a precautionary measure. Overnight the army and navy evacuated 26,000 people affected by the floods in Colombo. All schools in the country were closed on 20 May 2016.
Impact
Sri Lanka
As a depression, the cyclone brought torrential rains to Sri Lanka, causing flash flooding and landslides that killed 104 people. There were also 99 people reported missing. Additionally, the storm displaced over 134,000 people. Damage throughout Sri Lanka reached US$2 billion.
On 15 May, 137.7 mm (5.42 in) of rain was recorded in Katunayake. 373.3mm of rain fell on Kilinochchi in the 24 hours to 8.30 a.m. on 16 May 2016. Several parts of the capital Colombo were flooded. More than 35 families in Nalluruwa were displaced after a gale hit their homes. Bad weather forced two flights bound for Bandaranaike International Airport (BIA) to be diverted to Cochin International Airport. A landslide in Hattota near Dehiowita in Kegalle District left four dead and one missing.
Sri Lankan Disaster Management Centre (DMC) issued a flood alert on 16 May as the low-pressure area brought heavy rains to the country. The Kelani River and Maha Oya swelled as a result of the rainfall. With water levels on the Attanagalu Oya, Kalu Ganga, Kelani River, Maha Oya, Mahaweli River, Nilwala Ganga and Yan Oya rising, the Disaster Management Center (DMC) warned people living on river banks and low-lying areas in Badalgama, Dunamale, Giriulla, Hanwella, Horowpatana, Nawalapitiya, Panadugama, Peradeniya, and Ratnapura to be vigilant. The Sri Lankan Disaster Management Centre said that areas of the nation received the highest amount of rainfall since 2010. Landslides buried three villages in Kegalle District. Power failures were reported in several villages. Flights leaving Ratmalana Airport were grounded due to heavy rain. The Southern Expressway's exit at Biyagama was closed due to flooding. Heavy rains and floods affected Chilaw, Colombo, Galle, Kalutara, Kandy, Kegalle, Matara, Nuwara Eliya and Ratnapura and one person was killed by lightning in Anuradhapura. The Sri Lanka Air Force (SLAF) rescued fishermen off Pitipana near Negombo in Gampaha District after their boat capsized. A landslide in Ilukkwatta near Kadugannawa in Kandy District buried two homes under 25 feet of mud, rock and rubble, killing seven. A landslide in Samsarakanda near Aranayaka in Kegalle District buried several homes, killing 21 and leaving 123 missing. The villages of Elangapitiya, Pallebage and Siripura were buried in the landslide. A landslide at Kalupahana Estate near Bulathkohupitiya in Kegalle District buried several homes, killing 14 and leaving two missing. Two boys were killed in Wattala due to the floods. The Outer Circular Expressway was flooded at Kaduwela. With roads underwater and impassable, the Wilpattu National Park was closed until 25 May 2016. Water levels on the Kelani River, which had peaked at 8 feet, began to fall slowly on 19 May 2016 and had fallen to six feet by 22 May 2016. Two people were killed in Ambulgama near Hanwella on 20 May 2016 after the boat they were in capsized in flood waters. A landslide was reported in Kabaragalakanda near Aranayake on 21 May 2016.
India
Parts of Chennai and Tamil Nadu received between 93 mm (3.7 in) and 116.0 mm (4.57 in) of rain in a period of 24 hours. Kelambakkam, Chennai, received 226 mm of rainfall on 19 May. Later reports indicated that the city had received the highest rainfall in the month of May in over 2 decades. 12,000 personnel were deployed in the city to aid rescue operations. Multiple boats were stationed around the city for emergency rescue. In the low-lying areas, the National Disaster Response Force positioned 4 teams of personnel. An emergency number (1070) was set up. The IMD put the states of Andhra Pradesh and Odisha on an orange alert (the second highest level of emergency in India) on 19 May. The city of Kakinada recorded 174 mm (6.9 in) of rain in a day, the highest reported in the past 10 years. Bapatla reported 134 mm (5.3 in) of rain. Visakhapatnam District, Vizianagaram District and Srikakulam District were also affected by rains and were forecast to receive up to 210 mm (8.3 in) by 21 May. Chief Minister of Andhra Pradesh N. Chandrababu Naidu positioned 5 teams, each consisting of 100 personnel, in Krishna, East Godavari and Visakhapatnam districts.
Under the influence of the system, various places in Odisha received moderate to heavy rainfall. The reported rainfall was 96 mm (3.8 in) in Paradip and 85 mm (3.3 in) in Puri. Chief Minister of Odisha Naveen Patnaik readied 10 teams of Odisha Disaster Rapid Action Force and fire service personnel. Government of Odisha issued an alert in at least 12 districts in coastal, southern and northern regions of the state. The maximum temperature in Bhubaneshwar on 20 May was 26.2 °C (79.2 °F) compared to the average daily maximum temperature of 37.2 °C (99.0 °F) for the month of May. In West Bengal, Digha received 73 mm (2.9 in) of rainfall and Sagar Island received 96 mm (3.8 in) as the cyclone inched closer.
Bangladesh
Before the cyclone made landfall, over half a million people had been taken into shelters by the Government of Bangladesh. All flights at Shah Amanat International Airport were suspended. Restrictions were imposed on the movement of ships and ferries by Bangladesh Inland Water Transport Authority.
A storm surge up to 7 ft (2.0 m) above the astronomical tide hit the coast of Bangladesh at afternoon.
The cyclone approached the land over the coast at Sandwip, Hatia, Kutubdia, Sitakundu and Feni. The cyclone caused at least 26 deaths in seven districts across the country. 30 people died when Roanu hit the county, most of them died when the cyclone's storm surge overtopped dams. Around 40,000 homesteads and business houses were damaged.
The storm disrupted electricity supply and road communications in the areas. Food storage, seasonal crops were damaged. Livestock, including fish and shrimp firms were swept away. Damage across the nation were estimated at ৳10 billion (US$127 million).