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Informist, Friday, Aug. 1, 2025

LATEST DEVELOPMENTS

The spread and intensity of rainfall increased over parts of northeast India during the week, though it was not substantial enough to pull the region out of its monsoon deficit. The rise in rainfall activity over south peninsular India the previous week proved to be temporary, as the intensity of showers over the region decreased this week. Most parts of east, central, and northwest India continued to receive heavy to very heavy rainfall, while west India witnessed fewer showers.

A western disturbance persisted to the northwest of the country throughout the week while a well-marked low pressure area over Madhya Pradesh and Rajasthan slowly lost intensity. Remnants of the low pressure area emerged as an upper-air cyclonic circulation over the same region. Several other upper-air cyclonic circulations formed during the week, which were mostly concentrated over the northwestern and eastern regions of the country. A trough emerged at the beginning of the week, running from the Arabian Sea and extending eastwards inland.

The proximity of the multiple upper-air cyclonic circulations forming over the Bay of Bengal and Gangetic West Bengal brought some much-needed relief to parts of northeast India. Assam and Meghlaya saw heavy to very heavy rainfall during the week, while Nagaland, Mizoram, Manipur, and Tripura recorded some spells of heavy rainfall. 

Parts of Madhya Pradesh and Rajasthan saw extremely heavy rainfall during the first half of the week owing to the low pressure area over the region. With no active weather systems over the southern peninsula and western India, both regions only saw a few spells of heavy rain.

In the week ended Wednesday, India received an average rainfall of 78.8 millimetres, 19% above the normal of 66.3 millimetres for the week, according to the India Meteorological Department. In the southern peninsula, rainfall was 4% above average at 49.9 millimetres during the week, data from the bureau showed. Rainfall was 52% above the long-period average in central India at 117.1 millimetres. Rainfall was 2% below the long-period average in east and northeast India at 88.3 millimetres. In northwest India, rainfall was 5% below the average at 50.5 millimetres.

In the coming week, the intensity of rainfall is likely to decline further in south India, possibly pushing the region back into a state of deficit. Rainfall activity over central and west India is also expected to drop next week, the weather department said. Though a drop in showers over northwest is also expected, it is unlikely to cause any shortfall. Heavy to very heavy rainfall is likely to continue over northeast and east India 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. 1 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 rose more than 59% on year to 110.864 billion cubic metres as of Jul. 24, according to data from the Central Water Commission. The current level is 60.76% of the total live storage capacity of 182.461 billion cubic metres. According to data collated by Informist, the current water level in key reservoirs is at a six-year high. The water level as of Jul. 24 was 53.33% above the 10-year average for this period.

Reservoirs in the eastern region held 10.318 billion cubic metres of water as of Jul. 24, down from 10.995 billion cubic metres recorded on Jul. 17. The water level in reservoirs in the northern region stood at 10.194 billion cubic metres, or 51.35% of the total live storage capacity, up from 26.69% a year ago. 

In the western region, the water level in reservoirs was 23.299 billion cubic metres. As of Jul. 24, the water level was 62.37% of the total live storage capacity, compared with 39.88% a year ago. Reservoirs in the central region held 28.726 billion cubic metres or 59.12% of the total live storage capacity of 28 reservoirs in the region, up from 32.46% a year ago. 

The water level in the southern region was 38.327 billion cubic metres. As of Jul. 24, the water level was 69.76% of the total live storage capacity of the 45 reservoirs in the region. At this time last year, the water level was 48.17% of the total live storage capacity. 

SOWING

Above-normal rainfall has aided the progress of kharif sowing across the country. Farmers have sown kharif crops over 83 million hectares as of Jul. 25, 4% higher from 80 million hectares in the same period last year, according to data released by the Ministry of Agriculture and Farmers Welfare.

The area under paddy, moong, and maize rose from a year ago while that under tur, soybean, and cotton fell. The area sown with paddy was up over 13% at 24.5 million hectares. The acreage of coarse cereals, promoted as "Shri Anna" by the government, was up nearly 4% on year at 16.1 million hectares, mainly supported by a rise in the area under maize.

The area under pulses rose to 9.3 million hectares as of Jul. 25, up from 9.0 million hectares during the same period last year. Although total pulses acreage was up, the area under tur, the largest kharif legume, fell over 8% on year to 3.5 million hectares, the data showed. 

Oilseeds acreage fell over 2% on year to 16.7 million hectares due to a fall in soybean acreage. The area under cotton fell over 2% on year to 10.3 million hectares. Sugarcane acreage fell slightly to 5.52 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 Rajeev Pai

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