Context - Remal’s impact was severe in the Northeast because of its unusual trajectory. It developed over the east central Bay of Bengal on Saturday (May 25) evening and intensified into a severe cyclonic storm on Sunday morning over the north Bay of Bengal, with wind speeds clocking over 100 kmph
Unusual path of Remal
- The bay was unusually warm with some parts recording a temperature of 32 degrees Celsius (warm for water) which contributed to the intensity of the cyclone. A severe cyclone will rapidly weaken after it interacts with land, but Remal maintained its intensity as it moved to the northeast, causing unprecedented heavy rainfall, landslides, mudslides and flooding in that region.
Note – Exact reason for Remal’s unusual trajectory is still under investigation. However a related concept of recurving of cyclone is important from the examination’s perspective.
About Recurving of Cyclones
One of the most important aspects of cyclone track forecasting is recurvature, A cyclone track is said to recurve when it changes its path from the predominant zonal flow (normally westwards) to predominant meridional flow (normally northwards) and often again back to zonal flow in the opposite direction (normally eastwards).
The recurvature is said to be abrupt if the meridional flow is short-lived and there is sudden change in the direction of more than 60°.
Tropical cyclones in both the Northern and Southern Hemispheres tend to move westward and drift slowly poleward and then eastward. Trade winds are responsible for the general westward motion of tropical cyclones (Environmental steering).
Reasons for Recurving.
- Coriolis force drifts the cyclones towards right in N.H (Ferrell’s law) and hence pole wards and then eastwards (Beta Drift).
- Presence of subtropical highs, over oceans poleward of the trade winds. These regions of clockwise circulation in the Northern Hemisphere make the winds on the western edges of these large-scale circulations move toward the poles.
- Interaction of tropical cyclones with mid latitude westerlies change the original westward path of tropical cyclones towards north and then eastwards.
- Upper air jet streams further push the cyclones towards right.
- Interaction among several cyclonic wind system, a new avg point of centre is made and cyclones changes its path (Fujiwara effect).