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Informist, Friday, Sept. 19, 2025

LATEST DEVELOPMENTS

Most parts of the country received heavy to very heavy rainfall, with the extreme spells of rains limited to parts of northwest and east India in the first half of the week. The southwest monsoon began withdrawing from parts of Rajasthan on Sunday, three days ahead of its normal date of Sept. 17. However, the progression of the withdrawal paused on Tuesday after withdrawing from parts of Rajasthan, Gujarat, Haryana, and Punjab.

A well-marked cyclonic circulation over Southeast Asia is likely to travel towards the Bay of Bengal, merging with another cyclonic circulation which is seen forming over the region to form a stronger weather system, private weather forecasting agency Skymet said. The presence of this system and its interaction with the westerlies are likely to bring rainfall to most parts of the country, which could delay the exit of the southwest monsoon from central India, or the core monsoon zone, beyond the scheduled dates, the weather agency said.

The progression of the monsoon withdrawal usually 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 withdrawal is likely to stall for two weeks due to the presence of moisture and the possibility of continued rainfall over the country, a senior official at the India Meteorological Department told Informist.

Since Jun. 1, India has received 880.7 millimetres of rainfall, 8% above the normal of 817.2 millimetres, data from the India Meteorological Department showed. 

The presence of several cyclonic circulations, along with the formation of a few troughs joining these weather systems, continued to cause incessant rainfall over most parts of northwest India, though the strength and spread of showers fell from the previous week. Only parts of Himachal Pradesh and Uttarakhand faced very heavy to extremely heavy rainfall in the first few days of the week due to the presence of lower level monsoon easterlies. The extreme weather over these regions led to flash floods and landslides, causing widespread infrastructure damage and the loss of lives, according to media reports.

Northeast and east India continued to receive heavy to very heavy showers during the week due to the formation of multiple cyclonic circulations. However, this was still not enough to lift northeast India from its state of deficit.

Rainfall in west and south India remained staggered throughout the week, with no extremities recorded--neither a dry spell nor intense showers. The low pressure area which had formed over Telangana and Vidarbha in the previous week brought heavy to very heavy rainfall to the central parts of west and south India even as it continued to weaken throughout the week. Two troughs also formed over the region, with one spanning from Maharashtra to south interior Karntaka, and another one running from Karnataka to Kanyakumari. 

In the coming week, the intensity of rainfall over the country is expected to dip, with only moderate to heavy rainfall likely over most regions. Conditions are likely to become favourable for further withdrawal of the southwest monsoon from some more parts of northwest India and some parts of central India in the second half of next week, the weather department 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. 19 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

The meteorological department has projected the southwest monsoon to be above normal at over 106% of the long-period average of 870 millimetres, which is based on historical data from 1971 to 2020. The forecast assumes a modelling error of plus or minus 4%, according to the second-stage long-range forecast for the Jun-Sept southwest monsoon season. The department had earlier predicted rainfall for Jun-Sept at 105% of the long-period average with a modelling error of plus or minus 5%.

The agency said that on average it expects above-normal rainfall over most parts of the country this year except for northeast India, where rainfall is expected to be lower than normal. Central and south peninsular India are expected to receive above-normal rainfall at 106% of the long-period average, while rainfall over the northwestern parts of the country is likely to be normal at 92-108% of the long-period average.

Rainfall in September is likely to be above normal at 109% of the long-period average over most parts of the country, the India Meteorological Department said in its monthly outlook for rainfall and temperature. "Some parts of northeast and east India, many parts of extreme south peninsular India, and some parts of northern-most India, are likely to receive below-normal rainfall in September," it said.

Neutral Indian Ocean Dipole conditions are likely for the rest of the southwest monsoon season and weak negative Indian Ocean Dipole conditions are seen between the end of September and the beginning of October, the weather department said. Forecasts from the Monsoon Mission Climate Forecast System, along with other climate models, suggest that weak negative Indian Dipole conditions are likely to persist for a brief period at the end of the southwest monsoon, the department said. The Indian Ocean Dipole is the difference in surface temperatures between the eastern and western tropical Indian Ocean. A negative Indian Ocean Dipole leads to less rainfall in India and a positive index leads to more rainfall.

Neutral El Nino-Southern Oscillation conditions are expected to continue for the rest of the southwest monsoon, the weather bureau said. Weak La Nina conditions are likely to develop in the last quarter of the calendar year 2025, though neutral conditions are expected to return post December, the bureau said.

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, 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.

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 163.909 billion cubic metres as of Thursday, up nearly 4% on year, according to data from the Central Water Commission. The current level is 90% of the total live storage capacity of 182.479 billion cubic metres. The water level is 19.3% higher than the 10-year average for this period.

Reservoirs in the northern region held 18.672 billion cubic metres, which is 94% of the total live storage capacity, higher than 68.5% same period a year ago. In the eastern region, the water level in reservoirs was 17.089 billion cubic metres, nearly 79% of the total live storage capacity compared with 84% a year ago. 

The water level in the southern region was 48.838 billion cubic metres, which is 89% of the region's total live storage capacity across 45 reservoirs. At this time last year, the water level in the southern region was nearly 87% of the total live storage capacity.

The water level in reservoirs in the western region was 35.123 billion cubic metres. It is over 94% of the total live storage capacity, compared with over 93% a year ago. Reservoirs in the central region held 44.187 billion cubic metres or 91% of the total live storage capacity, slightly up from nearly 90.6% a year ago. 

Out of 161 reservoirs, 155 reservoirs reported more than 80% of normal storage and six reservoirs reported 80% or below of normal storage. Out of these six reservoirs none are having storage up to 50% of normal storage, the data showed.

SOWING

Above-normal rainfall has helped the progress of kharif sowing across the country. The total sown area under various kharif crops rose 1.4% on year to 111.08 million hectares as of Sept. 12, according to the agriculture ministry. 

Paddy acreage rose nearly 2% on year to 43.85 million hectares and the area under pulses increased nearly 1% to 11.81 million hectares. The acreage under pulses rose despite a fall in the area under tur to 4.58 million hectares from 4.63 million a year ago. 

The area under coarse cereals, promoted as 'Shri Anna' by the government, was up nearly 7% at 19.29 million hectares, mainly supported by the rise in area under maize. The acreage of maize rose about 13% to 9.48 million hectares. 

The acreage under oilseeds fell nearly 3% to 18.88 million hectares as farmers shifted to maize and paddy for better returns. The area under sugarcane rose nearly 3% on year to 5.73 million hectares whereas cotton acreage fell nearly 3% to 10.96 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

End

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. 

End

Reported by Shreya Shetty

Edited by Akul Nishant Akhoury

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