Most parts of the country have slipped under an extended cover of thundershowers over the past month, helping sustain a rainfall surplus to date.
The rain surplus as on Wednesday last added up to five per cent, with 21 out of the 36 Met subdivisions falling in the ‘excess’ or ‘normal’ category.
But fringes in the west, south-west and south, east and north-east continued to sit out and wilt under persistent deficit. Gujarat, Tamil Nadu and parts of the north-east are the worst-hit.
Only the north-east need entertain any hopes of reversal during the week ahead, according to international model forecasts.
This means that the projected line-up of thunderstorms from north to south will continue to evade Gujarat in the West, Tamil Nadu in the South and Odisha in the East.
In contrast, almost the entire half of north India, most of central India and the western half of peninsular India will witness continued thundershower activity during the week.
It will be particularly active over Kerala and adjoining coastal Karnataka, projections suggested.
The emerging pattern of thunderstorms sits well with the known pattern of pre-monsoon weather in which rising heat causes air to go up over land creating troughs of lower pressure criss-crossing it.
Moisture-laden winds from the surrounding seas blow into these troughs and interact with the prevailing hot air to set up localised thunderstorms.
Peninsular India has started to heat up appreciably with isolated places in Andhra Pradesh and Maharashtra already coasting into the mid-40-degree-Celsius mark. But thunderstorms and thunder squalls in north-west India have prevented the region from heating up in tandem.
The process is forecast to be delayed further since cooler western disturbances, low-pressure systems from across the border, are forecast to troop into Rajasthan/Punjab later into this week too.
India Met Department has forecast that heat-capping thunder squalls (seasonally knows as ‘aandhi’) will rip through the plains of north-west and east India.
The causative disturbance will meander into the landlocked north-east and interact with incremental supply of moisture from the Bay of Bengal to the south-west and spark off violent squalls and thunderstorms.
This will effectively signal the onset of Kal Baisakhi, the annual thunderstorm season in the east and north-east, which will extend right into the eve of onset of the monsoon over Kerala later in June.