The South-West monsoon, which is about three weeks away from its usual date of onset, will keep its time this year and arrive over Kerala on time around June 1 as per early indications available from national forecaster India Meteorological Department (IMD).

M Rajeevan, Secretary, Union Ministry of Earth Sciences MoES, said in a tweet, which read: ‘Monsoon 2021 update: @Indiametdept: Extended Range Forecast suggests monsoon will arrive over Kerala on time, around 1 June. This is an early indication. @Indiametdept official monsoon forecast on 15 May & rainfall forecast update around 31 May.

Next forecast dates May 15, 31

The next official monsoon forecast from the IMD on May 15 will come out with more details on this front followed by another on May 31 which would give a rainfall forecast update for the season. The first long-range forecast issued last month has already indicated a normal monsoon this year.

Meanwhile, the pre-monsoon activity over Kerala has intensified with thunderstorms, lightning and gusty winds being reported most parts of the state these days, an update from the IMD’s Chennai Meteorological Centre.

On Thursday, rain lashed many places over Kerala; a few places over Lakshadweep area, Coastal Karnataka and North Interior Karnataka; and at isolated places over Tamil Nadu, South Interior Karnataka, Coastal Andhra Pradesh, Rayalaseema and Telangana, the Chennai Met Centre said.

Low-pressure area likely

The pre-monsoon weather is being favourably influenced by a passing Madden-Julian Oscillation (MJO) wave, a cloud and rain-bearing wave that travels from West to East over the Indian Ocean periodically.

It impacts the tropical cyclone (low-pressure areas) and monsoon activity in this manner across the globe.

The enhanced rainfall phase of the MJO can also initiate the onset of monsoon seasons while the suppressed rainfall phase can delay monsoon onsets or set up a mid-monsoon ‘break’ evidenced best when rainfall activity shuts out for a brief or a medium-term depending on the wave amplitude.

An IMD assessment earlier this week had said that under the influence of the MJO wave, a low-pressure area’ is likely to form over central parts of the South Arabian Sea during May 14-20. There is a low probability of its intensification into a stronger weather system (likely storm/depression).

Pre-monsoon activity

This (Saturday) morning, the IMD said that the ongoing seasonal thunderstorm activity (Kal Baishakhi) over North-East India and parts of East India will continue variously over the hills and plains. A similar pattern on view over the South Peninsula too may persist for the next few days as well.

Isolated heavy rainfall is likely over Arunachal Pradesh on Sunday (tomorrow) and Monday; over Assam and Meghalaya on three days from Sunday; over Nagaland, Manipur, Mizoram and Tripura on Sunday and Monday; over the hills of West Bengal and Sikkim from today (Saturday) to Tuesday.

Isolated heavy to very heavy falls is forecast over Assam and Meghalaya on Monday. Thunderstorms and lightening accompanied with gusty winds is likely over most parts during next 4-5 days.

Seasonal trough, western disturbances

A seasonal but oscillating North-South trough over south Peninsula will trigger light/moderate scattered to fairly widespread rain/thunder over Kerala, Mahe, Lakshadweep and Coastal and South Interior Karnataka; and isolated to scattered rain/thundershower over the South Peninsula for next five days.

Isolated heavy rainfall is likely over Tamil Nadu, Puducherry and Karaikal today (Saturday) and over South Interior Karnataka on Tuesday, the IMD outlook said.

To the North, western disturbances interacting with easterly winds will cause scattered to fairly widespread rainfall/thundershowers very likely over the hills and isolated rainfall/thunderstorms over the plains during next three days. Intensity and distribution of rain may increase over the plains thereafter as moist winds (south-westerlies) blow in from the Arabian Sea.