The India Meteorological Department (IMD) has maintained a watch for a deep depression in the Bay of Bengal as a causative depression lay over the South-West Bay, closest to land about 190 km East of Trincomalee (Sri Lanka) but 430 km East-South-East of Nagapattinam, 520 km South-East of Puducherry and about 580 km South-South-East of Chennai along the Tamil Nadu coast, early this (Friday) morning.

It is likely to intensify further into a deep depression (only a rung below tropical cyclone status) during the course of today (Friday) and move along a track to the North-West along and off the East Coast of Sri Lanka, likely skirting the island nation, and head towards the North Tamil Nadu coast during the next two days.

An analysis of ocean and atmosphere features around the region indicate that the window for intensification is narrow given that sea-surface temperatures (SSTs) are a notch lower off the coast of Tamil Nadu, where it is expected to steam in sooner than later. Lower SSTs could impact evaporation and cloud-building and, in turn, storm strength and intensity.

Favourable wind shear

But lower SSTs are sought to be compensated by the decreasing tendency in wind shear values in the atmosphere (sudden change in wind speed and direction with height that destabilises the storm structure). The trend has turned favourable through the last 24 hours, with shear values decreasing during the period. This has even prompted the US Joint Typhoon Warning Centre to upgrade to ‘medium’ the potential for intensification of the system by Saturday (tomorrow), citing various global models. In a bulletin issued at 2.30 am this (Friday) morning, the US agency spotted the depression 773 km South-East of Chennai.

Showers for Sri Lanka

The Sri Lankan Meteorological Department located the depression 220 km to the South-East of Trincomalee at 5.30 am this (Friday) morning. It, too, expects the system to intensify into a deep depression later in the day (Friday) and move towards the Tamil Nadu coast.

Showers will occur at times in the Northern, North-Central and Eastern provinces of the island nation. Heavy showers, about 10 cm, can be expected at some places in these areas. Showers or thundershowers will occur at several places in Southern, Central and Uva provinces and in Ratnapura district during the evening or night. Fairly heavy showers above 50mm can be expected at some places in these areas.

More rain in another week?

A few showers may occur in the coastal areas of the South-West of the island in the morning. Winds speeding to 40-50 km/hr at times may prevail over the Northern, North-Central, Eastern, North-Western and Uva provinces and eastern slopes of the Central Hills and in Hambantota district.

An outlook for the second week of March (11-19) by the US National Centres for Environmental Prediction indicates the possibility of another wave of rain in the Bay of Bengal, pausing off the coast of Tamil Nadu after its southern flanks have impacted Sri Lanka. Numerical weather predictions from the IMD, too, suggests a sudden ramp-up in easterly winds from the northern flanks of a likely low-pressure area approaching the Sri Lanka and Tamil Nadu coasts by March 13.

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