Editorial 1 : Wetter & not that hot: Why is summer of 2025 atypical so far?
Context
A cooler-than-usual summer over large geographical areas of the country has contributed to keeping all-India average temperatures within the normal range
Unusual summer
- The summer of 2025 has been unusual so far.
- High day temperatures, typically reaching between 40 degrees and 45 degrees Celsius, and heatwave days have been largely absent.
- May, in particular, has been exceptionally wet in many parts of the country with thunderstorms accompanied by heavy rain and, in some cases, hail.
- No record-breaking temperatures have been reported from any part of the country .
- In March, maximum temperatures remained higher than normal over Central India, but the rest of the country experienced normal temperatures.
- But as a whole, the country’s Core Heatwave Zone (CHZ), spanning Central, North, and Peninsular India between Gujarat and West Bengal, which is prone to heatwave conditions every year from March to June and occasionally in July has not as yet experienced a significant heatwave episode this summer.
- A cooler-than-usual summer over large geographical areas of the country has contributed to keeping all-India average temperatures within the normal range.
Why this trend this year
- The primary reason for a wetter- and cooler-than-usual summer so far has been the frequent passage of streams of western disturbances in the lower latitudes.
- Western disturbances are eastward-bound winds that originate in the Mediterranean Sea and cause rain or snow along their way.
- There were four such episodes in March and April, and there have been two in May so far.
- There has also been a continuous incursion of moisture from the Bay of Bengal and Arabian Sea into the Indian mainland, with the subsequent wind interactions causing rainfall and thundershowers.
- Following a thunderstorm event, the maximum temperature generally falls by 5-7 degrees Celsius.
An especially wet May
- The month of May usually sees higher-than-normal temperatures, with North, Northwest and Central India experiencing heatwave conditions.
- Over the past three weeks, Northwest India has experienced thunderstorms resulting in above normal rainfall and normal or below normal maximum temperatures.
- The weekly all-India rainfall (May 2-8) stood at a 20% surplus. As a result, the maximum temperatures over the West, Central, and Eastern Indian regions dropped by 2-5 degrees Celsius below normal.
- In addition, below normal minimum temperatures (departure 1-3 degrees Celsius) were recorded over the East and Central India regions.
Conclusion
However, this year, the southwest monsoon is expected to hit the Kerala coast – considered the official onset of the southwest monsoon over India – on May 27. While onset is not an indicator of the future advance of the monsoon, if weather conditions are favourable, the possibility of a normal advance of the monsoon and an early onset over the country as a whole cannot be ruled out.