May 2003 disaster in Sri Lanka and cyclone 01-B in the Bay of Bengal

Heavy rainfall deluged South-Western Sri Lanka between the 11th and 19th of May 2003 and led to its worst disaster in 50 years. Floods and landslides claimed 260 lives. The World Meteorological Organization cited it as evidence for the increase of anomalous climatic extremes in recent years. Here, a meteorological analysis is presented of this disaster as part of a sustained effort to undertake meteorological applications for disaster management. There were intense low-level westerlies over Sri Lanka related to cyclone 01-B that made its way across the Bay of Bengal at least 700 km away. The southeastwardly traverse of the cyclone was stalled for a few days by anomalous north-westerly geostrophic winds over South Asia. Here, it is argued that orographic rainfall induced by this stalled cyclone and seasonal inter-tropical convergence zone cloud bands over Sri Lanka led to the deluge. The trajectory of the cyclone was remote from Sri Lanka and this led to no cyclone hazard warnings being issued. No cyclones have made landfall in Sri Lanka in May in the last 100 years. This study shows that one must exercise vigilance not only in the path of the cyclone but also remotely due to the modulation of the cyclone by other atmospheric phenomenon and topographic features. This flood may have been predicted with contemporary local area weather prediction models and this example points to the need for the development of local area weather prediction models as part of disaster warning systems. This study also demonstrates the use of meteorological diagnostics for post-event analysis of hydrometeorology of disaster events.