The Hindu Business Line : Monsoon winds lose steam; weak rainfall in Kerala

IN what is being described as a glaring evidence of intra-seasonal variability upsetting the monsoon applecart, prevailing southwesterlies ran out of steam overnight throwing up mostly sunny weather across Kerala on Tuesday.

Windspeeds lagged, failing to drive up incoming moisture high enough to cool and condense into rain, said Dr C. K. Rajan, Professor and Honorary Director of the Centre for Monsoon Studies at the Cochin University of Science and Technology (CUSAT).

The lull early into the onset phase is consistent with a trend in which dry episodes are becoming predominant and rainfall peaks increasingly fewer, Dr Rajan said. The exact cause for this eventuality is yet to be factually ascertained, and calls for deep and elaborate study.

Rainfall has been weak over the State on Tuesday. Kasaragod in the north reported an isolated heavy rain of seven cm. The other chief amounts of rainfall (in cm) are: Kudulu - five; Agathy - four; Punalur - three; and Kottayam and Vadakara - two each.

The topography of the land has been known to play a significant role in monsoon rainfall with moisture-laden currents being forced to rise against the Western Ghats, in turn producing copious rainfall on the windward side and considerably lower rainfall to the East. But flagging windspeeds do not allow for the vertical uplift of moisture, causing it to spread out horizontally instead and dissipate.

Intra-seasonal, inter-annual and even decadal variations in monsoon rainfall have all been accepted facts. The variations have spilled over into even the diurnal scheme of things, with rain gauge stations along the west coast and over the islands off the coast showing enhanced rainfall from midnight to morning hours.

On the other hand, those along the slopes of Western Ghats record rainfall maximum in the afternoon/evening hours.

Meanwhile, a routine weather update put out by India Meteorological Department on Tuesday said the southwest monsoon has further advanced over some more parts of the Central Arabian Sea, most parts of Coastal Karnataka, some more parts of South Interior Karnataka and Tamil Nadu. The northern limit of the monsoon passed through Karwar, Madikeri and Tiruchi.

The trough in the lower levels off the South Karnataka-Kerala coast shifted to an alignment off the fuller Karnataka-Kerala coast. The cyclonic circulation over Southwest Bay of Bengal lay over the Karnataka coast between 2.1 km and 5.8 km above sea level.

Forecast issued by the IMD indicated the possibility of rain/thundershowers at many places over Kerala, the Andaman and Nicobar Islands, Lakshadweep and Coastal Karnataka and at a few places in Interior Karnataka. The ongoing rainfall activity over Kerala, Coastal Karnataka and Lakshadweep is likely to continue.

A warning has been issued in terms of isolated heavy rainfall over Kerala, Lakshadweep, Coastal Karnataka and the Andaman and Nicobar.

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