THE ROLE OF INTRASEASONAL OSCILLATION IN THE TROPICAL CYCLONE ACTIVITY IN BAY OF BENGAL: A CASE STUDY FOR ROANU (2016)

Roanu (2016), the first tropical cyclone (TCs) in the Indian Ocean during 2016, originated from an atmospheric low pressure system over the oceanic area southeast of Sri Lanka around mid-May. After dumping heavy rainfall in Sri Lanka, it moved northeastward while upgrading into a tropical depression. It soon intensified into a tropical storm and then made landfall at Bangladesh four days later.Roanu is a relatively weak tropical cyclone. However, its intensity and track variations are very interesting. Both 10-20-day oscillation and 20-100-day oscillation have strong positive convection phase over the western BOB during the period, providing favorable conditions for the TC’s development. However, strong windshear inhibits its further intensification. The overall track direction is mainly controlled by the anomalous steering flow related to the 20-100-day oscillation. Roanu experiences twice direction adjustments while it moves northeastward, which might be related to the east-west oriented convection pattern of 10-20-day oscillation located at the west BOB during the TC passage. The 10-20-day oscillation induces anomalous northeastward flow anomaly and steer the TC away from the original direction (westward/eastward on 16-17/18-19 May). The importance of intraseasonal oscillation, including different components, should be fully considered in order to improve TC forecast skill, including the intensity change and landfall location.