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Informist, Friday, Oct. 3, 2025

LATEST DEVELOPMENTS

Though the spread and intensity of rainfall usually decrease during this time of the year, the presence of multiple weather systems over the country continued the spell of heavy to very heavy rainfall over most parts of the country this week. The continuation of rainfall has also impacted the progression of the southwest monsoon withdrawal, which has come to a stall since Sept. 24.

Although the southwest monsoon officially ends on Sept. 30, it completely withdraws from the country on Oct. 15. The declaration of withdrawal depends on the fulfilment of certain criteria, which include the absence of rainfall over the given region for at least a few consecutive days. The delay in its withdrawal is prolonging the monsoon's stay throughout the country. 

Currently, the line of monsoon withdrawal passes through Veraval and Bharuch in Gujarat, Ujjain in Madhya Pradesh, and Jhansi and Shahjahanpur in Uttar Pradesh. The withdrawal of the southwest monsoon from India may continue beyond Oct. 12, said Mrutyunjaya Mohapatra, director general, India Meteorological Department. The monsoon withdrawal began on Sept. 14 this season, ahead of the normal date of Sept. 17.

The well-marked low pressure area over central Maharashtra continued to move westwards and settled over the Gulf of Kutch during the week. It intensified further into a depression over the same region mid-week. Another low pressure area formed over the Bay of Bengal mid-week, which rapidly intensified into a well-marked low pressure area and further into a depression within the span of two days. 

The intensification of the above-mentioned weather system over the Bay of Bengal brought intense rainfall to most parts of east India during the week. The formation of two troughs joining the two weather systems--one each on the west and east coasts of the country--also brought rainfall to many parts of central India. Though the western coast also saw the formation and intensification of a low pressure area, most of the system remained over the Arabian Sea, with only its periphery close to the coast of Gujarat. As such, rainfall in west India was less intense during the week. 

South India recorded less rainfall than last week as no weather systems formed over the region. The peripheries of weather systems over other regions in the country brought moderate rainfall with a few spells of heavy showers over some parts of south India during the week. The formation of an upper air cyclonic circulation over northeast India caused heavy showers over the region. However, it was not enough to lift the region out of its state of deficit.

While the southwest monsoon has withdrawn from most parts of northwest India, a few parts of the region recorded rainfall due to the formation of a few upper air cyclonic circulations. 

In the coming week, the strength and spread of rainfall over the country is expected to decline. However, the formation of a western disturbance is likely to bring heavy to very heavy showers to most parts of northwest India, the weather department said. Hailstorms are also likely in some parts of northwest India, it said. The progression of the monsoon withdrawal is expected to remain stagnant next week as well, it said. 

Following is the weekly all-India rainfall since the beginning of the southwest monsoon season (in millimetres):

The following table gives homogeneous region-wise rainfall during Jun. 1-Sept. 30 in the country (in millimetres): 

MONSOON PROGRESS

This year, the southwest monsoon hit the Kerala coast on May 24, eight days ahead of its normal date of Jun. 1 and by May 29, the monsoon current covered southern and northeast India entirely, and parts of east and central India. However, after May 29, the monsoon was in a weak phase and resumed advancing only on Jun. 16. 

The monsoon covered entire India on Jun. 29, nine days before the normal date of Jul. 8. Normally, beginning Jun. 1, the southwest monsoon advances northwards and covers the entire country around Jul. 8. The withdrawal of the monsoon starts around Sept. 17 and it withdraws from the entire country around Oct. 15. 

ONSET CRITERIA

At present, the department uses criteria that was adopted in 2016 for declaring the onset of the monsoon over Kerala, which is based on the daily rainfall at 14 stations in Kerala and the neighbouring area, along with wind-field and outgoing long-wave radiation over the southeast Arabian Sea.

If, after May 10, 60% of the 14 designated stations--Minicoy and Amini in Lakshadweep, Thiruvananthapuram, Punalur, Kollam, Allapuzha, Kottayam, Kochi, Thrissur, Kozhikode, Thalassery, and Kannur in Kerala, and Kudulu and Mangalore in Karnataka--report rainfall of 2.5 millimetres or more for two consecutive days, the onset over Kerala will be declared on the second day, provided the wind-field and outgoing long-wave radiation conditions are met.

The outgoing long-wave radiation measures the amount of terrestrial radiation released into space and, by extension, the amount of cloud cover and water vapour that intercepts that radiation in the atmosphere.

The criteria emphasise the sharp increase in rainfall over Kerala along with the setting up of large-scale monsoon flow and extension of westerlies up to 600 hectopascal. 

However, the department declares the monsoon onset or progress dates for other regions operationally in a subjective manner, considering the sharp increase in rainfall and its characteristic sustenance for a few days and associated changes in the atmospheric circulation features.

LONG-RANGE FORECAST

For October, the weather department has forecast above-normal rainfall for the country at 115% of the long-period average. Most parts of India are likely to receive normal to above-normal rainfall during October. However, some areas in northwest India, the extreme south of peninsular India and isolated pockets in northeast India may experience below-normal rainfall, it said.

Normal to below-normal maximum temperatures are likely over most of India in October, except in the northeast and adjoining east India, the western Himalayan states, and Saurashtra and Kutch.

The weather agency said there is a 71% chance of the La Nia conditions forming during Oct-Dec. However, the current sea surface temperatures over the equatorial Pacific are near average, indicating neutral El Nio-Southern Oscillation. The El Nino-Southern Oscillation refers to the fluctuation between El Nino and La Nina conditions in the Pacific Ocean. El Nino, which means Little Boy in Spanish, is a climate pattern marked by an unusual warming of the surface waters in the Pacific, leading to drier and hotter weather in India. La Nina, which means Little Girl in Spanish, is the opposite of El Nino. It is an oceanic and atmospheric phenomenon that is associated with colder sea surface temperatures. La Nina is usually associated with good rains in India.

There are also weak negative Indian Ocean Dipole conditions prevailing. The weather bureau said that negative Indian Ocean Dipole conditions are expected to continue beyond the southwest monsoon season. A negative Indian Ocean Dipole results in less rainfall in India, whereas a positive index leads to increased rainfall.

The department's long-range forecasts are as follows:

Private forecaster Skymet has predicted a "normal" southwest monsoon at 103% of the long-period average with an error margin of plus or minus 5%. The agency had predicted a weak start to the monsoon this year but expects the rainfall to increase from July. It does not see any chance of the occurrence of El Nino.

PRE-MONSOON RAINFALL

While the monsoon arrived on May 24, the weather department said rainfall during May would not be factored into the southwest monsoon. The country received above-normal rainfall during the pre-monsoon period in Mar-May. India received 185.8 millimetres of rainfall during Mar-May, 42% above the normal for the period. Last year, it received 108.7 millimetres of rainfall during Mar-May, 8.1% below the normal for the period.

RECAP 2024
The country received 934.8 millimetres of rainfall in Jun-Sept last year, which was 108% of the long-period average. The monsoon hit the Kerala coast on May 30, two days ahead of the scheduled date, and covered the entire country by Jul. 2, six days ahead of the normal date of Jul. 8. The weather bureau's forecast for the monsoon onset over Kerala last year was May 31 and predicted rainfall during Jun-Sept 920.7 millimetres, or 96% of the long-period average.     

Overall, monsoon rainfall was above normal for the season and the spatial distribution was uniform. The rainfall in June was below-normal at 89% of the long-period average. However, the country received above-normal showers during the rest of the southwest monsoon period. Rainfall was 109% of the long-period average in July, 115% in August, and 112% in September.

Rainfall during the season was 107% of the long-period average in northwest India, 119% in central India, 86% in east and northeast India, and 114% in the southern peninsula. Of the total 36 meteorological subdivisions, two subdivisions received large excess, 10 received excess, and 21 recorded normal rainfall. Three subdivisions received deficient rainfall during Jun-Sept last year – Arunachal Pradesh, Punjab, Jammu & Kashmir, and Ladakh.

RESERVOIR LEVELS

The water level in 161 key reservoirs across India was 163.34 billion cubic metres as of Sept. 25, up nearly 3.5% on year, according to data from the Central Water Commission. The current level is 90% of the total live storage capacity of 182.48 billion cubic metres. The water level is 15.6% higher than the 10-year average for this period.

Reservoirs in the northern region held 18.25 billion cubic metres, which is 92% of the total live storage capacity, higher than 68% same period a year ago. In the eastern region, the water level in reservoirs was 16.98 billion cubic metres, nearly 78% of the total live storage capacity compared with 85% a year ago. 

Reservoirs in the western region held 35.86 billion cubic metres, which is 96% of the total live storage capacity, slightly higher than 95% a year ago. The water level in reservoirs in the central region was 44.74 billion cubic metres. It accounts for over 92% of the total live storage capacity, surpassing 90% from a year ago.

The water level in reservoirs in the southern region was 47.51 billion cubic metres or 86% of the total live storage capacity across the 45 reservoirs. The water level in the corresponding period last year was 85% of the total live storage capacity.

Out of the 161 reservoirs, 153 reservoirs reported more than 80% of normal storage, and eight reservoirs reported 80% or below of normal storage. Out of these eight reservoirs, six had storage levels between 51% and 60%, and two had storage levels between 61% and 70%, data showed.

SOWING

Above-normal rainfall has helped the progress of kharif sowing across the country. Farmers across the country have sown kharif crops over 112.1 million hectares as of Sept. 26, up nearly 1% on year, according to the agriculture ministry. Paddy acreage rose over 1% on year to 44.2 million hectares from last year. The area under pulses was also up nearly 1% on year at around 12 million hectares as of Friday. 

The area under coarse cereals, promoted as "Shri Anna" by the government, was up nearly 7% at 19.5 million hectares, mainly supported by a rise in the area under maize. Maize acreage rose nearly 13% to 9.5 million hectares as of Friday. 

However, the area under oilseeds declined over 5% on year to 19 million hectares. The area under soybean, the largest kharif oilseed, dipped to 12 million hectares from around 13 million hectares a year ago.

Similarly, the area under cotton fell nearly 3% on year to around 11 million hectares as of Friday. The area under sugarcane rose over 3% on year to 5.9 million hectares.

TERMS

LARGE EXCESS: Percentage departure of actual rainfall from normal rainfall is 60% or more 

EXCESS: Percentage departure of actual rainfall from normal rainfall is 20-59% 

NORMAL: Percentage departure of actual rainfall from normal rainfall is -19% to +19%

DEFICIENT: Percentage departure of actual rainfall from normal rainfall is (-)59-20%

LARGE DEFICIENT: Percentage departure of actual rainfall from normal rainfall is (-)99-60%

NORMAL: Percentage departure of actual rainfall is within +/-10% of the long period average

BELOW NORMAL: Percentage departure of actual rainfall is <10% of the long period average

ABOVE NORMAL: Percentage departure of actual rainfall is within >10% of the long period average

EXCEPTIONALLY HEAVY RAINFALL: Rainfall realised in a day is a value near about the highest recorded rainfall at or near the station for the month or season. However, this term will be used only when the actual rainfall amount exceeds 120 mm. 

EXTREMELY HEAVY RAIN: Amount of rainfall realised in a day is >/= 244.5 mm

VERY HEAVY RAIN: Amount of rainfall realised in a day is 124.5-244.4 mm

HEAVY RAIN: Amount of rainfall realised in a day is 64.5-124.4 mm

MODERATE RAIN: Amount of rainfall realised in a day is 7.6-35.5 mm 

RED ALERT: Very heavy rainfall of over 204.4 mm in 24 hours

ORANGE ALERT: Heavy rainfall of 115.6-204.4 mm in 24 hours 

YELLOW ALERT: Warning to be aware of worsening weather conditions that could disrupt daily life

Internet links:
India Meteorological Department - www.imd.gov.in
National Centre for Medium Range Weather Forecasting - www.ncmrwf.gov.in
Indian Institute of Tropical Meteorology - www.tropmet.res.in. 

Reported by Shreya Shetty

Edited by Akul Nishant Akhoury

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