November 2009 tropical cyclone Phyan in the eastern Arabian Sea: Oceanic response along west India coast and Kavaratti lagoon

Abstract

Spatial and temporal response of the coastal waters of eastern Arabian Sea (AS) and Kavaratti lagoon to the tropical cyclonic storm ‘Phyan’, which developed in the southeastern AS and swept northward along the eastern AS during 9–12 November 2009 and finally made landfall at the northwest coast of India, is examined based on time-series measurements of sea-surface wind (U10), gust, gust factor, barometric pressure, precipitation, atmospheric temperature, SST, and significant wave height from satellite-derived and in-situ measurements. The maximum wind-speed (U10) of ∼16 m/s occurred at Kavaratti Island region followed by ∼8 m/s at Dwarka in Gujarat, where the cyclone landfall occurred, and ∼7 m/s at Diu located just south of Dwarka as well as two southwest Indian coastal locations at Mangalore and Malpe. All other west India coastal locations recorded maximum wind speed of ∼5–6 m/s. Gust factor during peak storm event was highly variable with respect to topography, with steep hilly stations and proximate thick and tall vegetation exhibiting the largest value whereas coastal planes and Island stations exhibiting the least. Rainfall in association with Phyan was temporally scattered, with the highest 24-h accumulated precipitation (∼60 mm) at Karwar and ∼45 mm at several other locations. Impact of Phyan on the west India coastal waters was manifested in terms of intensified significant wave height (∼3 m at Karwar, Panaji, and Ratnagiri), sea surface cooling (∼5°C at Calicut), and surge flooding (∼80 cm at Verem). Several factors such as (i) water piling up at the coast supported by seaward flow of the excess water in the rivers due to heavy rains and westerly cross-shore wind, (ii) water piling down at the coast supported by the northerly alongshore wind (by virtue of Coriolis effect) and upstream penetration of seawater into the rivers, and (iii) possible interaction of upstream flow with river runoff, together resulted in the observed surge flooding at the west India coast. Despite the intense wind forcing, Kavaratti Island lagoon experienced insignificantly weak surge (∼7 cm) because of lack of river influx and absence of a sufficiently large land boundary required for the sustenance of wave/wind-driven water mass which tends to pile up at the land-sea interface.