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Sharp but brief showers interspersed with bright sun have highlighted transitional pre-monsoon weather over Thiruvananthapuram during the weekend as a rain-driving cyclonic circulation trough folded up in anticipation of the South-West monsoon.
Peak monsoon features only an offshore trough extending from South Gujarat to Thiruvananthapuram, into which south-westerlies dump moisture from the Arabian Sea to fall as heavy to very heavy rain. The monsoon reached the South Arabian Sea a couple of days ago and is waiting the signal to lunge forward and precipitate the onset along the Kerala coast.
Emerging negative IOD
Monsoon watchers are also assessing conflicting vibes from the East Indian Ocean, where early signs of a negative Indian Ocean Dipole (IOD) are emerging. It can potentially weigh on the strength of the cross-equatorial flows that make the monsoon. This is quite unlike the situation in 2019 when a strong positive IOD had warmed up the West Indian Ocean boosting the monsoon to a historic high.
India Meteorological Department (IMD) said on Sunday strong cross-equatorial winds continue to blow into the Bay of Bengal. It predicted fairly widespread to widespread rain with thunder squall, lightning and gusty winds for the Andaman & Nicobar Islands for the next five days and isolated heavy falls on Monday. Squally weather (wind speeds reaching 40-50 kmph gusting to 60 kmph) is likely over East-Central Bay and adjoining North Andaman Sea.
Strong flows in Bay
In the next three days, a circulation forming over the warm East Indian Ocean (just below the Equator and to the South of East Bay) will help further strengthen the south-westerly monsoon flows into the larger Bay. These flows would interact with land-based circulation and a western disturbance, allowing moisture-laden south-easterly flows to blow deeper into East and North-East India (including Jharkhand, Bihar and Uttar Pradesh) and bring rain.
Heat wave conditions have mostly abated from entire country with maximum temperatures of above 39 degree Celsius confined to extreme West Rajasthan on Friday.
Heat wave abates
The other weather highlight during the weekend was heatwave conditions abating over most parts of the country thanks to the combined influence of the monsoon in the Bay and movement of cooler western disturbances from across the international border into North-West, Central, East and North-East India.
On Sunday, the IMD located a disturbance over South-West Uttar Pradesh while a successor was waiting over Central Afghanistan. An East-West trough runs from a cyclonic circulation over South-West Uttar Pradesh to Jharkhand across South-East Uttar Pradesh. A cyclonic circulation each hovered above Punjab and Odisha. Together, they will trigger fairly widespread to widespread light, moderate rain, isolated thunderstorms, lightning and gusty winds over the region until Tuesday, with peak rainfall intensity on Monday.
Rain for East, North-East
Towards the East, scattered to fairly widespread light to moderate rainfall with isolated thunderstorms, lightning, gusty winds are likely over Bihar, Jharkhand, plains of West Bengal and Odisha during the next five days. Isolated thunder squalls may roam Odisha, the plains of West Bengal and Jharkhand. Strong south-westerly winds from the Bay will cause widespread light to moderate rain, thunderstorms and lightning over North-East India.
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