After an agonising wait of at least 10 days, the monsoon has advanced into parts of South-West Bay of Bengal, more parts of South-East Bay, entire Andaman & Nicobar Islands, the Andaman Sea and some parts of East-Central Bay on Wednesday in what appears to be initial signs of its broad-based progress to both sides of Peninsular India (Bay of Bengal and the Arabian Sea).

India Meteorological Department (IMD) said conditions are favourable for its further advance into some parts of Maldives and the Comorin area on the Arabian Sea side; some more parts of the South-West Bay; remaining parts of the South-East Bay; some more parts of the Central Bay; and some parts of the North-East Bay (closer to Myanmar) during the next two-three days.

Heavy rain forecast

Earlier in the morning, the IMD forecast the possibility of heavy rainfall at isolated places over Kerala and Coastal and South Interior Karnataka on Tuesday and Wednesday around the time of the usual onset of the monsoon though there is no sight of it anywhere near. The rain would instead be triggered by the atmospheric response to the movement of a deep western disturbance, the second on a trot, across North, North-West and East India.

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A five-day outlook by the IMD said light to moderate fairly widespread rainfall with thunderstorms, lightning and gusty winds are likely over Kerala and Lakshadweep while it will be scattered over South Interior Karnataka, Tamil Nadu and Andhra Pradesh. 

Warming of Arabian Sea

The Arabian Sea is warming up very fast on the lines of the Bay of Bengal that had hit sea-surface temperatures of 32℃ and threw up the near-super cyclonic storm Mocha earlier this month. In hindsight, it is becoming clear the cyclone was instrumental in delaying the progress of the monsoon in the extreme South-East Bay where the IMD declared its onset on May 19. In this context, the warming of the East-Central Arabian Sea to as high as 32℃ already on Tuesday bears close watching. 

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A few global models have hinted at cyclone formation in the Arabian Sea around the time the monsoon will likely make a delayed onset during the first week of June. An IMD model too tends to subscribe to this possibility timed towards the end of the first week of June or early second. If this were to happen, its onward progress could get impacted adversely.  

Maze of circulations

A western disturbance lies as a North-West to South-East trough from North-East Pakistan to Western India, extending deep down to Mumbai. An offspring cyclonic circulation lies over South-West Rajasthan and adjoining Pakistan. An East-West trough runs from the cyclonic circulation over to North-West Madhya Pradesh. A third North-South trough runs from a cyclonic circulation over South Chhattisgarh to Interior Tamil Nadu. 

Volatile weather

These formations are capable of setting up volatile weather in these regions. Apart from South India, light to moderate scattered to fairly widespread rainfall with thunderstorms, lightning and occasional gusty winds/squall (speeds of 40-50 km/hr gusting to 60 km/hr) are likely over North-West India till Wednesday with peak activity on Tuesday and gradual reduction from Thursday. The monsoon cannot enter the mainland till such time as these formations dissipate and cease to exist.

Hailstorms are likely over North Rajasthan, the Jammu division and Himachal Pradesh on Tuesday and over Uttarakhand until Wednesday. Thunder squalls/gusty winds with speed reaching 60-70 km/hr are likely over Rajasthan on Tuesday and over Uttarakhand on Wednesday. Heavy rainfall is likely at isolated places in Jammu & Kashmir and Himachal Pradesh on Wednesday.. 

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