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Informist, Friday, Aug. 29, 2025

LATEST DEVELOPMENTS

Monsoon conditions intensified across the country during the week, with most of the heaviest showers concentrated over northwest India due to the presence of several weather systems. Incessant rainfall continued to batter parts of east and central India while west and south India also received heavy rainfall with a few spells of very heavy showers. Northeast India continued to face a deficit in rainfall for the second consecutive week.

Multiple upper air cyclonic circulations formed over the country during the week, with a few troughs coming up between some of the circulations, intensifying rainfall in the northern half of the country. Two successive western disturbances formed to the northwest of the country while the monsoon trough remained in its normal position for most of the week. Two low pressure areas formed over the Bay of Bengal, with one of them strengthening into a well-marked low pressure area mid-week. The presence of a shear zone, running roughly along the latitude 17 degrees north — which runs across Maharashtra, Karnataka, Telangana, and Andhra Pradesh — contributed to heavy showers in parts of west and south India.

The slow movement of the two western disturbances over north India, with the second disturbance becoming more active and interacting with southeasterly winds, increased the spread and intensity of rainfall across northwest India, the India Meteorological Department said. In particular, Jammu recorded exceptionally heavy rainfall this week, which resulted in multiple landslides, flash floods, and large-scale infrastructure damage. 

Northwest India has received 594.0 millimetres of rainfall since Jun. 1, of which 245.6 millimetres was recorded so far in August. Of the total rainfall seen in August, 95.7 millimetres or nearly 40% was recorded during the week ended Wednesday, according to the weather bureau's data.

From Jun. 1-Aug. 29, the country as a whole recorded 727.6 millimetres of rainfall, which is 6% above the normal of 686.8 millimetres, as per the weather department. 

The formation and strengthening of the low pressure systems over the Bay of Bengal continued the spell of heavy to very heavy rainfall over east and central India this week. The presence of several upper-air cyclonic circulations also contributed to the continuous spell of showers over the region. 

The movement of the low pressure area across central India, along with the presence of the shear zone, intensified rainfall over most parts of internal west India, such as Vidarbha, central Maharashtra, Saurashtra, and Kutch. The shift of the weather system also strengthened the westerlies along the Konkan coast, continuing the wet spell over the western coasts during the week. 

Under the influence of the above-mentioned weather systems, the western coasts of south peninsular India, and all other states in the region except Tamil Nadu recorded heavy to very heavy rainfall during the week. The absence of any active weather systems kept northeast India just as dry as last week, with only some parts of the region recording a few spells of heavy rainfall during the week. 

In the coming week, the intensity of rainfall is expected to reduce over northwest India, though it is unlikely to face any deficit. A slight dip in monsoon conditions is also likely over most parts of west, south, east, and central India, though staggered showers will continue over these regions. Heavy rainfall is expected over several parts of northeast India in the first half of next week.

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-Aug. 29 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 over the country is likely to be within the normal range of 94-106% of the long-period average in August, the India Meteorological Department said. Normal to above-normal rainfall is very likely over many parts of the country except parts of central India, western parts of peninsular India, northeast India, and some parts of eastern and northwest India where it is likely to be below normal.

In August and September, above-normal rainfall is expected at 106% of the long-period average. The intensity of rainfall is likely to decrease across the country in August and pick up again in September. The bureau has forecast normal rainfall over the country in August and above-normal rainfall in September. 

Neutral Indian Ocean Dipole conditions are also being observed over the Indian Ocean at present, the weather 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.

The bureau said that currently neutral El Nino-Southern Oscillation conditions are prevailing over the equatorial pacific region and similar conditions are expected for the remaining part of the monsoon. 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 152.309 billion cubic metres as of Thursday, up nearly 7% on year, according to data from the Central Water Commission. The current level is over 83.5% of the total live storage capacity of 182.479 billion cubic metres. The water level is over 21% higher than the 10-year average for this period.

Reservoirs in the northern region held 18.076 billion cubic metres, which is over 91% of the total live storage capacity, higher than 60% during the same period a year ago. In the eastern region, the water level in reservoirs was 14.736 billion cubic metres, which is nearly 68% of the total live storage capacity, compared with 66% a year ago. 

The water level in the southern region was 47.143 billion cubic metres, which is nearly 86% of the region's total live storage capacity across 45 reservoirs. At this time last year, the water level in the southern region was over 82% of the total live storage capacity. The water level in reservoirs in the western region rose to 32.571 billion cubic metres from 30.453 billion cubic metres a week ago. It is now over 87% of the total live storage capacity, compared with 82% a year ago. 

Reservoirs in the central region held 39.784 billion cubic metres or nearly 82% of the total live storage capacity, down from 84% a year ago.

The number of reservoirs in the country with water level at 100% of normal storage capacity was unchanged from a week ago at 15, the data showed. Of the 161 reservoirs in the country, 96 reported more than 80% of normal storage. Of the remaining 65 reservoirs, 12 have water that is not more than 40% of normal storage, down from 15 a week ago.

SOWING

Above-normal rainfall has helped the progress of kharif sowing across the country. Farmers have sown kharif crops on 107.4 million hectares as of Aug. 22, up over 3% on year, according to data released by the Ministry of Agriculture and Farmers Welfare. 

Paddy acreage rose around 8% on year to 42 million hectares and the area under pulses rose over 1% on year to 11.3 million hectares as of Friday. The area under tur declined nearly 2% on year while moong acreage rose over 1% and urad acreage was up around 7% on year. 

The acreage of coarse cereals, promoted as 'Shri Anna' by the government, rose over 6% on year at 18.7 million hectares, mainly supported by a rise in the area under maize. The area under maize rose to 9.3 million hectares from 8.4 million hectares a year ago. 

However, the area under oilseeds declined nearly 3% on year to 18.2 million hectares. The area under soybean, the largest kharif oilseed, dipped to 12 million hectares from 12.5 million hectares. Groundnut acreage fell to 4.5 million hectares from 4.7 million hectares. The area under jowar and bajra were nearly unchanged from a year ago at 1.4 million hectares and 6.7 million hectares, respectively. Similarly, the area under cotton fell nearly 3% on year to 10.8 million hectares. 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. 

Reported by Shreya Shetty

Edited by Subhojit Sarkar

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