Monsoon season enters last lap

Withdrawal period extended as the southwest monsoon fails to follow its timetable for bidding adieu

 
By Akshay Deoras
Last Updated: Thursday 17 September 2015

Withdrawal period extended as the southwest monsoon fails to follow its timetable for bidding adieu

September 30 this year will be an ordinary Tuesday for most people but it will be a special one for the southwest monsoon. Monsoon’s epic journey, which started around mid-May this year, will be coming to an end on September 30 as the season officially ends that day. All India rainfall during June 1 to September 4 is 14 per cent less than the normal rainfall. Believe me, it’s a pretty satisfactory number unlike what was being anticipated when the season commenced amidst an El Niño buzz. The El Niño which was supposed to shape rainfall pattern in these months didn’t turn up, but the monsoon which was supposed to fail in its performance performed very well.

Let’s have a look at the monsoon’s performance over the three months. 

Source: India Meteorological Department (IMD)

The above image shows rainfall in India during the period June 1 to September 1, 2014. Monsoon performed the best in southern interior Karnataka as this subdivision recorded excess rainfall (+23 per cent of the normal). Twenty out of the 36 meteorological subdivisions recorded normal rainfall (-19 per cent to +19 per cent of the normal) whereas 13 subdivisions recorded deficient rainfall (-20 per cent to -59 per cent of the normal). Monsoon performed the worst in the two subdivisions of Punjab and Haryana-Chandigarh-Delhi, which reported “scanty” rainfall (about -65 per cent of the normal rainfall).

Numerous thunderstorms in Rajasthan, north India and along the monsoon trough (extending from Rajasthan in south-eastern direction) on September 3. Image courtesy University of Dundee

However, a low pressure region developed over Rajasthan that triggered thunderstorms and rains along much of north India that highly improved this situation. Jammu and Kashmir, due to heavy rains which created flooding in the western part of the state, plunged into the “normal rainfall” category from “deficient” along with western Rajasthan. Rains in Punjab also improved as the state entered the “deficient” category from the previous “scanty” category. Rainfall couldn’t improve the situation that much in Delhi-NCR region.

The present rainfall statistics


Image courtesy- IMD

  • All India rainfall during June 1 to September 4 is 14 per cent less than normal.
  • 22 Subdivisions are reporting normal rainfall, 12 are reporting deficient, 1 is reporting excess and 1 is reporting scanty rainfall.
  • Only 7 out of 22 subdivisions (reporting normal rainfall) have recorded more than the normal rainfall (positive values in the bracket).
  • In the same period, rainfall departures are -13 per cent in east and north-east India, -29 per cent in north India, -11 per cent in central India, and -5 per cent in southern India.
  • 3 per cent of the total area of India has seen excess rainfall till now, 64 per cent has seen normal rainfall, 32 per cent has seen deficient rainfall, and 1 per cent has seen scanty rainfall.


2014 Monsoon withdrawal delayed

Normal Monsoon withdrawal dates. Courtesy IMD

In my blog published in early August, titled "Monsoon data’s departure from reality", I had mentioned, “ideally, the southwest monsoon withdraws from Rajasthan and parts of Punjab by September 15, but there has been some delay in this process the past few years because of which monsoon withdraws completely from north India only by end of September. Due to this delay, the monsoon withdrawal is delayed in Rajasthan as well.”

Indeed, we see that happening now. Monsoon hasn’t withdrawn yet from Rajasthan and this means there is a delay in the monsoon withdrawal process in this year. So the monsoon has forgotten its timetable again.

This year for most of the places it didn’t arrive on time and now it isn’t leaving the nation on time.

From this weekend, there will be a significant reduction in the rainfall in north India and the maximum temperatures will jump back to 35°C and above. Long range weather models (predicting the weather for more than five days from now and which are not so reliable) are indicating a decrease in the moisture in north India at 850mb level (at 5,000 ft above ground) from around mid-September. IMD says: After September 1, monsoon withdrawal can happen from the western parts of Rajasthan or Punjab (Referred as extreme NorthWest India) if: 1) No rainfall is reported for at least five consecutive days in the region; 2) moisture content in the troposphere (lowermost part of troposphere where the weather systems exist) decreases; 3) a high pressure system is established between ground level to 5,000 ft above ground.

So, if the long range weather models are to be believed, monsoon withdrawal will likely begin around mid-September from western Rajasthan. It's too early to say when the southwest monsoon will completely withdraw from India.

Monsoon rainfall statistics to improve further

A fresh low pressure from Bay of Bengal is expected to travel through southern parts of central India this weekend. This will bring heavy rains in Odisha and Chattisgarh on Saturday; and northern Telangana and northern Karnataka on Sunday. Vidarbha (southern Maharashtra) will be getting good rainfall along with Madhya Pradesh in this period. Heavy rains will be spreading into western, southern Maharashtra and western Madhya Pradesh on Monday. Eastern coastal areas of Gujarat like Surat and, possibly, Mumbai will get heavy rains around Tuesday-Wednesday; so, people in these areas should follow the weather. Excluding these areas, rainfall will be on a decline in rest of India.

As a result, the all India rainfall situation will further improve in India and the rainfall departure of India and central India division will come down.

Punjab will once again plunge into “scanty” rainfall category and don’t expect any further improvement in the rainfall in north India, including the subdivision Haryana-Chandigarh-Delhi. This subdivision is likely to end up as the region that received the worst rainfall in India this season.

*Note : The rainfall figures given in the blog were obtained on September 4 and they will vary with time. For the latest rainfall statistics, click here

Akshay Deoras is an independent weather forecaster

Subscribe to Weekly Newsletter :

Comments are moderated and will be published only after the site moderator’s approval. Please use a genuine email ID and provide your name. Selected comments may also be used in the ‘Letters’ section of the Down To Earth print edition.