The monsoon has kicked off fresh rain waves from both the Arabian Sea and the Bay of Bengal with India Meteorological Department (IMD) forecasting fairly widespread to widespread rainfall with isolated heavy to very heavy falls over Karnataka, Tamil Nadu and Kerala during the next three-four days.

Satellite pictures (this Wednesday) showed rain clouds spreading out over Chennai, Tirupathi, Bengaluru, Vellore, Mysuru, Salem, Puducherry, Coimbatore, Tiruchirappalli, Nagapattinam, Madurai and Tirunelveli across Tamil Nadu and Karnataka with rains lashing some parts of the region.

A forecast for the rest of today from the Chennai Regional Meteorological Centre of the IMD said that heavy to very heavy rain may lash isolated places over Kerala. In fact, massive cloud bands from the Arabian Sea had raided its southern districts from Tuesday and dropped heavy rain overnight.

Rain for Karnataka, Tamil Nadu

The Chennai Met Centre said that heavy rain is likely at isolated places over Theni, Dindigul, Tenkasi and Kanyakumari districts of Tamil Nadu, parts of South Interior and Coastal Karnataka. As for Thursday, heavy to very heavy rain is forecast for Kerala and Coastal Karnataka as the rain belt moves to the North.

Heavy rain is also forecast over the Theni, Dindigul, Tenkasi and Kanyakumari districts of Tamil Nadu and adjoining South Interior Karnataka for Thursday. The day after (Friday) would likely see the heavy rain belt pouring it down not only over Kerala and Karnataka but also over Andhra Pradesh and Telangana.

The proximate causes for the spurt in rains over the South Peninsula, which has been devoid of any significant amounts in the recent past, are the enhanced flows over the Arabian Sea and a cyclonic circulation over the South-East Bay of Bengal, with one complementing the other.

Circulation in the Bay

The cyclonic circulation was located a short distance to the South-East of the Nagapattinam coast with associated south-easterlies and easterlies mopping up the moisture from the Bay and massing it up in the form of clouds along the Tamil Nadu coast and the adjoining interior Peninsular India.

The short-to-medium range guidance from the IMD suggests that it would move West-North-West and cross the Coastal Andhra Pradesh coast before weakening. The system would also have dragged the leading monsoon current to rain it down over Karnataka, Andhra Pradesh and Telangana.

The system would have weakened just to cede time and space for the North-East Bay of Bengal to conjure up its own circulation into the next week, which could go on to become a weak low-pressure area. This is expected to cross land across Odisha-West Bengal and enter the monsoon trough from August 5.

More rain for North-East

The monsoon trough has not yet started moving down from the Himalayan foothills, but is expected to do so from Thursday. A cyclonic circulation has formed over the hills of West Bengal, which could lead to widespread rainfall with isolated heavy to very heavy falls over Uttarakhand, Uttar Pradesh, Bihar, hills of West Bengal and the North-Eastern States today (Wednesday) and on Thursday.

A similar forecast is valid for Punjab, Haryana, Chandigarh, Delhi, Himachal Pradesh and Madhya Pradesh until Friday in line with the movement of the trough. The IMD has warned that isolated extremely heavy falls may lash the hills of West Bengal and Sikkim today (Wednesday) and on Thursday.