The Southwest Monsoon made an early entrance over Kerala on May 24 this year, arriving nearly a week ahead of its normal June 1 onset.

While such an early onset is rare, it’s only the third time in over three decades that the monsoon has arrived before May 25, it doesn’t automatically translate to an equally early arrival across the rest of India.

In fact, when it comes to Odisha, the road the monsoon takes is influenced by a complex chain of atmospheric processes, many of which are currently in motion.

So, how soon will the rains reach Odisha, and what determines that timeline? Here's a detailed look at the science behind monsoon progression and the latest forecasts driving this year's rainy season.

Monsoon Onset: What It Means and How It Travels

The Indian Southwest Monsoon begins when the Inter-Tropical Convergence Zone (ITCZ), a band of low pressure, moves northward from the equator during late May and early June. This triggers a large-scale inflow of moist southwesterly winds from the Arabian Sea and Bay of Bengal toward the Indian subcontinent.

Once the monsoon hits Kerala, it usually takes around 10 to 15 days to travel up the east coast and reach Odisha, a process that depends on several factors:

- The strength and continuity of monsoon winds.

- Formation of low-pressure systems in the Bay of Bengal.

- Temperature differentials across land and ocean.

- The Madden-Julian Oscillation (MJO): a tropical wave pattern that enhances convection.

Historically, Odisha sees the onset of the monsoon between June 10 and June 12. But this year’s early Kerala onset, paired with dynamic weather systems in the Bay of Bengal, may bring rain much sooner.

ALSO READ: Know the guidelines followed to declare southwest monsoon onset

What’s Happening in 2025: The Case for Early Arrival in Odisha

According to the India Meteorological Department (IMD), a low-pressure system is expected to form over the west-central and adjoining north Bay of Bengal by May 27. This is significant as low-pressure systems are major rain triggers in Odisha, often acting as atmospheric pathways that pull in monsoonal moisture from the south.

If the low-pressure area strengthens and draws in the monsoon flow from the Bay, Odisha could see an official monsoon onset earlier than the historical average, potentially by the first week of June or even earlier.

The Science: Why a Low-Pressure System Matters

In the Bay of Bengal, low-pressure systems act as catalysts that can “pull” the southwest monsoon current northward and inland. These systems help accelerate the monsoon's progress across the eastern and central parts of the country.

Here’s How:

Enhanced Moisture Convergence: The low-pressure area creates a vacuum effect, drawing in moisture-laden winds from the Arabian Sea and Bay of Bengal.

Vertical Wind Shear: Such systems increase vertical motion in the atmosphere, which is critical for the cloud formation that brings sustained rainfall.

Strengthening of Monsoon Trough: The northward stretch of the monsoon trough is crucial for aligning Odisha and the eastern coast with the main monsoon flow.

If the upcoming low-pressure system matures by May 27–28 and remains stationary for a few days, it could significantly accelerate the arrival of the monsoon in Odisha.

ALSO READ: Cyclonic circulation over north coastal Odisha, low pressure around May 27; IMD issues orange alert for heavy rainfall

Will Above-Normal Rainfall Follow?

Another encouraging sign comes from the IMD’s seasonal outlook. Released in April, the forecast projected above-normal rainfall for the 2025 monsoon season.

Importantly, there is no El Niño in play this year, often a red flag for weak or erratic monsoons. Instead, the neutral to La Niña conditions expected in the Pacific Ocean are generally favourable for strong monsoon performance.

This aligns with the pattern we’re already seeing: strong pre-monsoon systems, early onset in Kerala, and active atmospheric conditions in the Bay.

While IMD has not yet declared an official monsoon onset date for Odisha, the confluence of scientific indicators suggests the rains could arrive much earlier than the usual June 10–12 window.