New Delhi, Oct. 31 -- Delhi recorded the coolest October in three years, with ample rainfall and overcast skies keeping the day temperature in check. The average monthly maximum temperature stood at 31.5degC - 1.5degC below the long period average (LPA), which was Delhi's lowest since it was 31.4degC in 2022, India Meteorological Department (IMD) data showed. This has largely been down to Delhi recording 89.3mm of monthly rainfall this month - nearly six times the LPA of 15.1mm, a surplus of 491%, data showed. This was also Delhi's wettest October in three years, with Delhi logging 128.6mm of rainfall. Last year, zero rainfall was recorded and 5.4mm was recorded in 2023. Overall, this is the third wettest October in the last decade, IMD said. "In October, particularly the first half, Delhi saw ample rain. Western disturbances, including the most recent one, even without rain resulted in cloudiness, making days cooler and nights warmer," said Mahesh Palawat, Skymet vice president. The monthly rainfall was recorded between October 1 and 8, with the highest single day spell of 38mm falling on the first day of the month. Meanwhile, the average monthly minimum stood at 20.1degC, marginally above normal. Typically, when overcast skies prevail, days are cooler with nights warmer as clouds prevent heat from being lost into the atmosphere An IMD official said even with an early withdrawal of the south-west monsoon, western disturbance and other weather systems have played a role. "The first-half of the month saw active western disturbances. We then saw mainly clear skies, but a reversal again occurred with the latest western disturbance," official said. The highest maximum temperature this month was 35.7degC, recorded on October 2, while the lowest day-time temperature was 26.4degC, logged on October 26. However, as the monsoon withdrew and wind speeds dropped mid-October, the capital's air quality began to deteriorate. Central Pollution Control Board (CPCB) data shows that city's average air quality index (AQI) for the month stood at 224, in the 'poor' category. This was marginally better than last year's 234 but worse than the 218 recorded in 2023 and 210 in 2022. The AQI on Thursday touched 373, the highest for any October in three years. HT had earlier flagged data gaps, with only 9 out of Delhi's 39 air quality stations having complete hourly data on Diwali day and the day-after. Dipankar Saha, former head of CPCB's air laboratory, said the air quality deteriorates every October post the withdrawal of the south-west monsoon. "It is triggered by the stagnation of air due to poor ventilation coefficient and low wind speed. The Indo-Gangetic Plain suffers from low wind speed and a low thermal boundary layer, resulting in poor ventilation in winter months. It doesn't mean that we should not pay attention to emissions control."...