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Three months of swinging Celsius

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The middle of February is when the chill begins to abate. The middle of May is when the monsoon is longed for. In our towns, district headquarters and cities, that climatic journey of 90 days is one of a steady rise in the reading of the temperature gauge, from the low 20s to the mid 30s.

This large panel of 90 days of daily average temperatures shows, in 57 ways, the effects of the rains that almost every district has experienced during the last two months. For each city, the curved line is the long period ‘normal’ for these 90 days, based on daily averages. Also for each city, the second line which swings above and below the ‘normal’ is the one that describes the changes in its daily average from February to May 2015.

[You can download (1.52MB) a full resolution image of the panel here.]

Where this second line crosses to rise above the normal, the intervening space is red, where it dips below is coloured blue. The patches of red or blue are what tell us about the effects of a lingering winter, or rains that have been called ‘unseasonal’ but which we think signal a shift in the monsoon patterns.

The 90-day temperature chart for Goa, with daily averages nearer the long period normal over the latter half.

The 90-day temperature chart for Goa, with daily averages nearer the long period normal over the latter half.

Amongst the readings there is to be found some general similarities and also some individual peculiarities. Overall, there are more blue patches than there are red ones, and that describes how most of the cities in this panel have escaped (till this point) the typical heat of April and May. The second noteworthy general finding is that these blue patches occur more frequently in the second half of the 90 days, and so are the result of the rainy spells experienced from March to early May.

Hisar (in Haryana) has remained under the normal temperature line for many more days than above or near it. So have Gorakhpur (Uttar Pradesh), Pendra (Chhattisgarh), Ranchi (Jharkhand), Nagpur (Maharashtra) and Jharsuguda (Odisha).

On the other hand in peninsular and south India, the below ‘normal’ daily average temperature readings are to be found in the latter half of the time period, coinciding with the frequent wet spells. This we can see in Kakinada, Kurnool and Anantapur (Andhra Pradesh), Bangalore, Gadag and Mangalore (Karnataka), Chennai, Cuddalore and Tiruchirapalli (Tamil Nadu) and Thiruvananthapuram (Kerala). [A zip file with the charts for all 57 cities is available here (1.2MB).]

What pattern will the next 30 days worth of temperature readings follow? In four weeks we will update this bird’s eye view of city temperatures, by which time monsoon 2015 should continue to give us more blues than reds. [Temperature time series plots are courtesy the NOAA Center for Weather and Climate Prediction.]