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Informist, Friday, Sept. 12, 2025

LATEST DEVELOPMENTS

Though most parts of the country continued to receive staggered rainfall, the intensity and spread of showers reduced due to the weakening of prominent weather systems during the week, especially over northwest India. Rainfall in most parts of central and east India remained plentiful while only a few parts of west India and south India saw heavy to very heavy showers. The dry spell over northeast India began to break mid-week, bringing much-needed relief to the region.

Since Jun. 1, India has received 836.2 millimetres of rainfall, 7% above the normal of 778.6 millimetres, data from the India Meteorological Department showed.

The well-marked low pressure area, which had formed over parts of west and northwest India last week, intensified into a depression while moving north-westwards during the beginning of the week. It further intensified into a deep depression over Gujarat and Rajasthan, continuing the spell of intense showers over parts of Gujarat, Rajasthan, and Punjab. The regions were relieved from the heavy downpour in the next 48 hours, when the weather system weakened back into a depression and moved further away.

By mid-week, the depression had moved towards Pakistan and weakened further into a well-marked low pressure area. The proximity of the weakened weather system, along with the formation of a few cyclonic circulations and troughs associated with them, continued the wet spell over northwest India mid-week onwards, with only a few spells of heavy showers recorded over the region thereon.

Several upper air circulations formed over most parts of east and central India during the week. The concentration of a few of these systems, along with the formation of a trough brought very heavy to extremely heavy showers over parts of Odisha, sub-Himalayan West Bengal, and Sikkim during the week.

In west India, most of the intense showers recorded during the week occurred over the interior regions, such as Saurashtra, Kutch, central Maharashtra, Maharashtra, and Vidarbha. The proximity of the weather system strengthening and later weakening over northwest India brought the majority of the showers over these regions while the rest of west India only received light to moderate rainfall this week.

Similar conditions persisted over south Peninsular India. The presence of several cyclonic circulations over east India led to the formation of troughs which ran from east to south interior Karnataka, restricting most of the intense rainfall to the eastern parts of the peninsula, such as Andhra Pradesh, Telangana, Tamil Nadu, and the interiors of Karnataka.

The intensity of rainfall over northeast India increased in the second half of the week, with the formation of a few cyclonic circulations over the region. However, it was not substantial enough to lift the region from its state of deficit.

In the coming week, the strength of rainfall is expected to remain the same over India, with moderate to heavy rainfall predicted over most of the country. The spread of rainfall over parts of west and south India, which saw a dry phase this week, is expected to increase, though the intensification of showers is unlikely to be worrisome. Conditions are also likely to become favourable for the withdrawal of the southwest monsoon from some parts of northwest India towards the end 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. 12 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 158.765 billion cubic metres as of Thursday, up nearly 2.5% on year, according to data from the Central Water Commission. The current level is 87% of the total live storage capacity of 182.479 billion cubic metres. The water level is nearly 15% higher than the 10-year average for this period.

Reservoirs in the northern region held 18.243 billion cubic metres, which is nearly 92% of the total live storage capacity, higher than 68% in the same period a year ago. In the eastern region, the water level in reservoirs was 16.220 billion cubic metres, which is nearly 75% of the total live storage capacity compared with over 76% a year ago.

The water level in the southern region was 46.300 billion cubic metres, which is over 84% 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 88% of the total live storage capacity.

The water level in reservoirs in the western region was 34.174 billion cubic metres. It is over 91% of the total live storage capacity, compared with 90% a year ago. Reservoirs in the central region held 43.829 billion cubic metres or over 90% of the total live storage capacity, up from nearly 89% a year ago.

Out of 161 reservoirs, 145 reservoirs reported more than 80% of normal storage and 16 reservoirs reported 80% or below of normal storage. Out of these 16 reservoirs two 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. Farmers across the country have sown kharif crops over 110.5 million hectares as of Sept. 5, up nearly 2.5% on year, according to data released by the Ministry of Agriculture and Farmers Welfare.

Paddy acreage rose nearly 5% on year to 43.8 million hectares and the area under pulses was up nearly 2% on year at 11.6 million hectares. The area under pulses rose despite a drop of over 1% on year in the area under the largest kharif legume, tur, at 4.5 million hectares. The fall in the area under tur was offset by a significant rise in urad acreage. The area under urad was up over 9% on year at 2.3 million hectares while that under moong was largely steady from the year-ago period.

The acreage of coarse cereals, promoted as 'Shri Anna' by the government, was up nearly 7% on year at 19.2 million hectares, mainly supported by a rise in the area under maize. The acreage of maize rose over 12% on year to 9.5 million hectares.  

However, the area under oilseeds declined nearly 3% on year to 18.7 million hectares, as farmers shifted to maize and paddy due to better returns. The area under soybean, the largest kharif oilseed, dipped to 12.0 million hectares from 12.6 million hectares. Groundnut acreage was nearly unchanged from a year ago at 4.7 million hectares.

Similarly, the area under cotton fell nearly 3% on year to 10.9 million hectares as of Sept. 5. The area under sugarcane rose nearly 3% on year to 5.7 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 Ashish Shirke

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