Cyclone Arnab and Delhi rain: will it clean the air before Diwali? Only for a day or two

Yes, Delhi is likely to get rain this week, but it will probably clean the air for only a day or two, and none is forecast for the run-up to Diwali. The India Meteorological Department (IMD) forecasts light rain with thunderstorms on Thursday 29 October and very light rain on 30 October 2026, then no rain from 31 October to 3 November (IMD Regional Meteorological Centre New Delhi, 28 October, 6 pm). Diwali is on Sunday 8 November, beyond IMD's seven-day forecast.

Delhi's air is Poor today. CPCB's 4 pm bulletin put the city's 24-hour average AQI at 229 on 28 October, up from 197 the day before (CPCB, 28 October). Each time it rained in Delhi this October, the AQI fell, and each time it was back up within one to three days.

Key findings

• Rain on 29 and 30 October, then dry. IMD's Delhi office expects gusts of up to 50 km/h on 29 October.
• Rain cleaned the air for about a day. CPCB's AQI for Delhi fell to 83 on 12 October after 41.6 mm of rain and was 158 the next day. It fell to 90 on 16 October, then rose to 159.
• One stormy night. On 24 October the mean PM2.5 across Delhi's monitors fell from 151 µg/m³ at 9:30 pm to 30 at 2:30 am. By 8:30 pm the next day it was back above 100.
• Diwali smoke undoes rain. In 2023, rain two days before Diwali cut Delhi's AQI from 437 to 218 on Diwali day. The next day it was 358.

Is Cyclone Arnab bringing rain to Delhi?

Not directly, as far as IMD's bulletins say. Arnab crossed the Andhra Pradesh coast near Narsapur early on 28 October as a very severe cyclonic storm and is expected to move north-north-west and weaken (IMD all-India bulletin, 28 October, 5:48 pm). Our Andhra Pradesh story covers the coast.

For the north, the same bulletin lists two western disturbances (low-pressure systems that travel east from the Mediterranean region) and a cyclonic circulation over north-west Uttar Pradesh. It does not name Arnab as the cause of Delhi's rain. Down To Earth reported that Arnab's remnants could move towards Uttar Pradesh and Nepal, and that meeting a western disturbance could bring intense rain to parts of northern India and Nepal; it did not mention Delhi (Down To Earth, 26 October).

What IMD forecasts for Delhi, day by day

Source: IMD Regional Meteorological Centre New Delhi, issued at 6 pm on 28 October 2026. IMD's national bulletin is a little stronger for Haryana, Chandigarh and Delhi together: widespread rain on 29 and 30 October, thundersqualls gusting to 70 km/h, isolated hail, isolated showers on 31 October, and dry from 1 November (IMD, 28 October).

What about Diwali on 8 November?

It is too far out for a firm forecast. IMD's extended range model guidance, the latest on its website on 28 October, shows less than 1 mm of rain a day over Delhi for 5 to 12 November, about normal for the season (IMD extended range forecast). That is a model outlook, not a forecast for Diwali day.

IITM's Air Quality Early Warning System expects Delhi's air to be Poor on 28 October, Moderate from 29 to 31 October, then Moderate to Poor for the six days after (IITM, 28 October). So expect a cleaner few days around the rain, then calmer, drier air into November. Our Diwali 2026 air quality guide covers firecracker rules and how to protect your home.

What rain did to Delhi's air this October

Delhi had three measured rain spells this month. Our explainer on whether rain reduces Delhi pollution covers how washout works. CPCB's bulletin is a 24-hour average to 4 pm, so night rain shows up in the next day's figure.

Rain: IMD via Asianet Newsable, 13 October, PTI via ThePrint, 15 October and India TV, 26 October. AQI: CPCB bulletins for 12, 13, 16, 17 and 25 October, and the days either side.

The heaviest rain gave the cleanest day, 83 (Satisfactory) on 12 October, but the next afternoon Delhi was back in the Moderate band. After the light rain of 25 October, the AQI climbed for three days in a row; the month's peak so far is 245 on 21 October.

Our monitor data agrees. Mean daily PM2.5 fell from 56.0 µg/m³ on 10 October to 36.9 on 11 October, the cleanest day of the month. (Our archive has a gap across India from 12 to 14 October.) Around the 15 October rain it went from 78.3 to 47.2, then 58.7 and 90.9.

Rain with thunderstorms and strong winds reached Delhi NCR late on 24 October (IANS via SocialNews, 25 October). The mean PM2.5 across Delhi's monitors was 151 µg/m³ in the hour from 9:30 pm and 30 at 2:30 am, a fall of four-fifths in five hours. It was back to 101 by 8:30 pm on 25 October.

Why light rain is not a clean-up

• Heavy rain helps, briefly. A Centre for Science and Environment (CSE) study of six rain events in Delhi this monsoon found PM2.5 fell about 19.5% while it rained. Within 48 hours of the rain stopping it was 11.1% above where it started (CSE, 30 September).
• A drizzle can make it worse. In humid air, fine particles absorb moisture and swell; studies reported by Republic World found weak showers can push PM2.5 higher (Republic World, 10 July). IMD's forecast for 30 October is very light rain.
• Wind does much of the work. The 24 October drop came with a storm. IMD expects winds to ease to 5 to 10 km/h by 2 November.
• Fireworks spike it. Rain does not stop traffic, dust or burning, and Diwali night adds a sharp burst of smoke on top.

The last time it rained just before Diwali

In 2023, Diwali fell on 12 November. Safdarjung recorded 6 mm of rain in the 24 hours to 8:30 am on 10 November, and IMD officials said a wind shift from north-west to south-east would reduce smoke from stubble burning (PTI via National Herald, 10 November 2023).

Source: CPCB bulletins for 9, 10, 12 and 13 November 2023. The rain took Delhi from Severe to Poor; one night of fireworks took it back to Very Poor.

Where Delhi's air is worst this week

Mean daily PM2.5 from 21 to 27 October 2026, among 45 monitors with at least five full days:

DPCC is the Delhi Pollution Control Committee; IITM is the Indian Institute of Tropical Meteorology. On 27 October, the last full day, the mean of all monitors was 109.6 µg/m³, close to October's worst, 116.6 on 20 October. See every monitor on our Delhi live air quality page.

GRAP and farm fires

GRAP Stage I is still in force. At 5 pm on 28 October, the website of the Commission for Air Quality Management (CAQM) showed Stage I of the Graded Response Action Plan in force since 21 October (CAQM). Stage II starts above an AQI of 300. What each GRAP stage does.

Farm fires are rising. Punjab recorded 717 stubble burning incidents up to 27 October, according to the Punjab Pollution Control Board, led by Tarn Taran (318) and Amritsar (154) (IANS via SocialNews, 28 October). IMD forecasts easterly and south-easterly winds over Delhi from 29 to 31 October, and some north-westerly wind, the direction from Punjab, on 2 and 3 November. More in our Punjab stubble burning tracker.

What to do

• Use the clean hours after rain to air your home, and close windows when the reading climbs.
• Stay indoors in thunderstorms. IMD's national bulletin has isolated hail on 29 and 30 October.
• Prepare for Diwali now: N95 or FFP2 masks and purifier filters. People with heart or lung conditions should follow their doctor's advice and official health guidance.

How we measured

• Data. Hourly PM2.5 from 48 Delhi monitors run by CPCB, DPCC and IITM, the network CPCB's bulletin uses. No satellite or low-cost sensors.
• Days. Our days run 5:30 am to 5:30 am India time (UTC days); CPCB's run to 4 pm. Use ours to compare monitors and days, CPCB's for the official band.
• Valid days. At least 18 hours of readings. We dropped 194 of 1,238 monitor-days from 1 to 27 October, 84 of them on 12 and 13 October, when our archive has a gap. No gaps were filled, and no monitor was frozen.
• Hourly chart. The mean of 39 to 46 monitors each hour; times are the start of each hour, India time.
• Today. Our 28 October figures cover 5:30 am to 5:30 pm only.

Our India NAQI figures are the mean of hourly values, which runs higher than CPCB's 24-hour bulletin. Live readings: Delhi, Noida, Gurugram and Ghaziabad.