Weather Bee: How is monsoon performing this year

The monsoon arrival this year was far earlier than in the past. It arrived on the Kerala coast on May 24, eight days before schedule

India’s monsoon season, the country’s main rainy season, runs officially from June to September. With data for the first 12 days of the 122-days season now in, how does rain’s performance look like in the 2025 monsoon? The answer to this question has been complicated this year by the early arrival of the monsoon weather system. According to the gridded data of the India Meteorological Department (IMD), the first 12 days of June have been unusually dry. However, this does not mean that the weather system did not bring the usual amount of rain. It just means that the rain expected in the first half of June fell before the usual first day of the monsoon. This makes the early arrival of monsoon this year a mixed bag. Here’s why.

Children play football at Kothi Beach after rain stopped during monsoon season, in Kozhikode, Kerala, on May 27. (PTI)

In official analysis, rain’s performance during the southwest monsoon season is usually tracked from June 1. This is because June 1 is the usual date when the atmospheric conditions that make the season rainy arrive on the Kerala coast, its first point of contact on mainland India. While monsoon had arrived earlier than this date on 22 occasions in the 54-year period from 1971 to 2024, most of these early arrivals were close to the June 1 date. For example, of the 22 years of early arrivals, the arrival was in the 29-31 Ma period in 12 years. Therefore, an analysis of the monsoon based on June rain would not miss much rain brought by the weather system in these 12 years.

However, the monsoon arrival this year was far earlier than in the past. It arrived on the Kerala coast on May 24, eight days before schedule. It had arrived by May 24 or earlier only in five years before 2025. Therefore, an analysis based on June rain alone would miss more than a week’s worth of rain that the monsoon system caused this year. For example, compared to a 1971-2020 average – IMD considers this the Long Period Average (LPA) of rain for tracking its performance currently – of 45.8 mm rain, India has received only 31.6 mm rain in the first 12 days of June, a 31% deficit. This also makes the 2025 monsoon the 32nd driest since 1901. However, this might mislead in one way. From May 24 to May 31, India received 59.24 mm rain, 29% more than the LPA for the first 12 days of June. In other words, if the rain in the last eight days of May had fallen in the first 12 days of June, 2025 monsoon would be ranked the 26th rainiest.

India’s monsoon season, the country’s main rainy season, runs officially from June to September. With data for the first 12 days of the 122-days season now in, how does rain’s performance look like in the 2025 monsoon? The answer to this question has been complicated this year by the early arrival of the monsoon weather system. According to the gridded data of the India Meteorological Department (IMD), the first 12 days of June have been unusually dry. However, this does not mean that the weather system did not bring the usual amount of rain. It just means that the rain expected in the first half of June fell before the usual first day of the monsoon. This makes the early arrival of monsoon this year a mixed bag. Here’s why.

In official analysis, rain’s performance during the southwest monsoon season is usually tracked from June 1. This is because June 1 is the usual date when the atmospheric conditions that make the season rainy arrive on the Kerala coast, its first point of contact on mainland India. While monsoon had arrived earlier than this date on 22 occasions in the 54-year period from 1971 to 2024, most of these early arrivals were close to the June 1 date. For example, of the 22 years of early arrivals, the arrival was in the 29-31 Ma period in 12 years. Therefore, an analysis of the monsoon based on June rain would not miss much rain brought by the weather system in these 12 years.

However, the monsoon arrival this year was far earlier than in the past. It arrived on the Kerala coast on May 24, eight days before schedule. It had arrived by May 24 or earlier only in five years before 2025. Therefore, an analysis based on June rain alone would miss more than a week’s worth of rain that the monsoon system caused this year. For example, compared to a 1971-2020 average – IMD considers this the Long Period Average (LPA) of rain for tracking its performance currently – of 45.8 mm rain, India has received only 31.6 mm rain in the first 12 days of June, a 31% deficit. This also makes the 2025 monsoon the 32nd driest since 1901. However, this might mislead in one way. From May 24 to May 31, India received 59.24 mm rain, 29% more than the LPA for the first 12 days of June. In other words, if the rain in the last eight days of May had fallen in the first 12 days of June, 2025 monsoon would be ranked the 26th rainiest.

Chart 1

To be sure, not all of the 59.2 mm rain that fell in the last eight days of May was monsoon rain. The western arm of the monsoon has covered only around half of Maharashtra, Telangana, southern Chhattisgarh and Odisha, and it took two days (although this is disputed) to reach these places from Kerala. Similarly, the monsoon’s eastern arm took five days after May 24 to cover north-eastern states. It has not progressed beyond these places since. This means that the rain in the period between monsoon’s arrival over Kerala and these places was not exactly monsoon rain. Similarly, any rain that the northern half of India received was not exactly monsoon, although it has contributed to the May average for India.

Map 1

So how does one make sense of the rainfall this monsoon season? It may not be wrong to study rain’s performance by the LPA for the period one is looking at, since June is indeed drier than the LPA this year across large parts of the country. Moreover, although the monsoon usually does not arrive by June 13 in northern India, pre-monsoon showers do bring rain in the region. The limited point of the analysis above is that the early arrival of monsoon over Kerala has not also meant a swift progress over northern India. While rain in late May brought relief from summer heat for most of the country, it may not have been beneficial from the perspective of farmers.