The European Centre for Medium-Range Forecasts indicate heavy rain over the West Coast (Kerala to Konkan); Madhya Maharashtra, Marathwada; Telangana; Karnataka; and north Tamil Nadu for the next four to five days (until May 20).
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Myanmar declared the onset of the monsoon on May 13, the same day that the India Meteorological Department (IMD) announced its arrival over extreme south-east Bay of Bengal and south Andaman Sea. Rains have also checked into the Maldives, IMD said on Thursday.
The next major station ahead of the Kerala coast is Sri Lanka. On Thursday, the Lankan Met Department warned of thundershowers and severe lightning across western, central, Uva, the eastern, and the north-central provinces and Mullaittivu and Vavuniya districts.
Monsoon onset window
The winds will be monsoon-friendly westerly to south-westerly at 30-40 km/hr and may escalate to 50-60 km/hr at times in the seas extending off Puttalam to Pottuvil via Colombo, Galle and Hambantota. Wind field projections indicate the onset window here could likely be open from Friday (May 16), signalling an early onset over the island nation, ahead of its usual date of May 22.
Onset dynamics over Lanka are expected to touch off over Kerala that lies at a flying distance of about 30 minutes to the north-west. Numerical models support a scenario where wind speeds at lower and higher levels at Kerala latitudes align with the required strength, intensity and depth as early as from May 20 (against predicted date of May 27 with model error of four days).
Pre-monsoon peak
As already reported, this phase will be preceded by ferocious pre-monsoon weather over the west coast and the adjoining interior peninsula. For the next five days, IMD has predicted moderate rain, thunderstorms, lightning and gusty winds over Kerala and Mahe; Tamil Nadu, Puducherry, and Karaikal; coastal Andhra Pradesh and Yanam; Rayalaseema; Telangana; and Karnataka.
Thunder squalls with winds reaching 50-60 km/hr and gusting to 70 km/hr are likely over Telangana, coastal Andhra Pradesh and Yanam; Rayalaseema; and North Interior Karnataka. Isolated heavy rainfall is likely over Tamil Nadu for three days; over interior Karnataka for five days; coastal Andhra Pradesh, Telangana, and Rayalaseema for two days; and Kerala & Mahe for three days.
Spread-out elsewhere
Over West India, moderate rainfall, thunderstorms, lightning and gusty winds (30-50 km/hr) are likely over Konkan and Goa; Madhya Maharashtra; and Marathwada for four days. Thunder squalls (50-60 km/hr gusting to 70 km/hr) are likely over Madhya Maharashtra; Marathwada; and Konkan & Goa, while isolated heavy rainfall is forecast over Madhya Maharashtra.
A similar forecast is valid for two other geographical regions of North-West India and the East and North-East India. Heat waves may keep away from most parts of the country. Mid-May and June are known to generate severe to very severe heat waves. They help develop required temperature and pressure gradients visa-a-vis land and sea for the monsoon to drive into the mainland.
Required gradients
Land heats up and cools down faster, and this is what helps set up temperature and pressure gradients. Winds blow from an area of higher pressure (seas, which are cooler) to that of lower pressure (land, which is hotter). Hot air rises over land and moisture-laden winds from the seas blow inward to replace it. This leads to formation of clouds and rainfall, and sustains the monsoon.
Published on May 15, 2025
