Number Theory: Is this an unusually warm October?

Here are four charts which explain this in detail

“Statistically no, but anecdotally yes,” is the short answer to the question. The longer answer is that because large parts of India saw an unusually rainy and hence not-so-warm September, even a return to otherwise usual temperatures in October might feel warmer than usual to people in large parts of northern, central, and peninsular India. Here are four charts which explain this in detail.

HT file photo

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  At the country level, October is unusually warm only at night

  The average maximum for the country as a whole is 31.77°C this October so far (up to October 13), according to the gridded data of the India Meteorological Department (IMD). This is roughly same as the 1981-2010 average, considered the normal for temperature by the IMD, of 31.73°C. But minimum temperatures are indeed much warmer than normal this October. The average minimum for the month so far, at 21.99°C, is 1.06°C warmer than normal and ranked 7th highest since 1951. This suggests that for a country as a whole, October is warmer than usual only at night, which is what minimum temperatures indicate.
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  Part of the reason for this is just the regional variation in maximum temperatures

  To be sure, regional extremes have a role to play in day time temperatures (this is what maximum temperatures indicate) appearing normal at the country level. 69% of the country has experienced a maximum temperature warmer than normal and 32% of the country has averaged a maximum more than 1°C warmer than normal in the month so far. Places where the maximum has been warmer by more than 1°C are concentrated in Kerala, Karnataka, Maharashtra, Andhra Pradesh, Telangana, Odisha, Chhattisgarh, Jharkhand, West Bengal, and Uttar Pradesh. At least a third of these states has experienced an average maximum more than 1°C warmer than normal. However, this is being compensated by a deviation in the opposite direction in north-eastern states (except Mizoram), Gujarat, Jammu and Kashmir and Ladakh. Around a third or more of each of these states has experienced a maximum at least 1°C cooler than normal.
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  However, October days may feel warmer than usual also because they are warmer than in September

  While 32% of the country has experienced a maximum in October warmer by more than 1°C compared to normal, the proportion of the country where the maximum in the month so far is warmer than September by more than 1°C is 57%. This is why people may feel that October is unusually warm even if the month’s maximum temperatures are close to normal or only marginally warmer than normal. Delhi and its neighbouring districts (IMD’s gridded data for temperature does not allow one to calculate an average for Delhi alone) are a good example of this. October for this region is 0.08°C cooler than normal by maximum temperature, but 1.62°C warmer than September. Therefore, people in Delhi and neighbouring areas may feel October to be warmer than usual simply because October is warmer than September, whereas they are used to temperatures decreasing after September. This has happened because average maximum for September this year was 1.74°C cooler than normal for Delhi and neighbouring districts. This trend of October temperatures bucking their usual trend and rising compared to September, has also played out across most of the country, as the accompanying maps show.
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  Rain trends in September and October have a role to play in this

  As explained above for Delhi, October feels warmer than normal largely because September was much cooler than normal. This happened largely because the southwest monsoon’s withdrawal has been delayed this year. Therefore, September was rainier than usual in large parts of northwestern India, central India, and even peninsular India states like Andhra Pradesh and Telangana. October would get colder than September in these regions only if it continued to rain here in October. However, it has either not rained or rained very little in these regions in the month so far. This is what has led to October feeling warmer than normal even in places where that is not the case.