September 30, 2015 marks the official end of the South West Monsoon Season for 2015.
Though monsoon has withdrawn from most of India North of Vindhyas, it is expected to linger in Goa for a few more weeks in October.
Even then, September end is the right time to look at the performance of the SW Monsoon in Goa for 2015.
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| Fig 1a |
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| Fig 1b |
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| Fig 1c: Source - http://www.imdgoa.gov.in |
During September 2015, Goa received normal rainfall. Area weighted average rainfall rainfall of 293 mm was recorded against normal of 280 mm (+5%). However due to deficient rains in June, July and August, the cummulative rainfall recorded was just 2389 mm (94 inches), against normal 2972 mm (117 inches). This resulted in deficiency of -20% for the seasonal.
As per IMD norms, for seasonal rainfall at regional level, rainfall between -20% to -59% is classified as deficient.
However though September yielded +5% rainfall, there were just 9 days out of 30 days in September with rainfall more than 3 mm, as recorded by Vagaries Goa Rain Gauge at Aquem, Margao.
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| Fig 2 |
Canacona recorded the highest rainfall during September and Dabolim the lowest.
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| Fig 3a |
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| Fig 3b |
September 2015 rains were also lower than September 2014 rains.
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| Fig 4 |
As expected the foothills of Western Ghats received the highest rainfall during the season. However what was unexpected was Sanguem, in South Goa with 3079 mm (121 inches), outperforming Valpoi , the usual topper, at just 2741 mm (108 inches). Surprisingly too Pernem in North Goa, which usually receives good seasonal rainfall, received poor rainfall with just 1865 mm (73 inches).
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| Fig 5a |
And in Google Earth with seasonal rainfall in mm:
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| Fig 5b |
The month-wise rainfall chart shows that while Sanguem received good rainfall every month, Valpoi received poor rains in September.
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| Fig 6 |
Comparing the seasonal rainfall at all the rain centers in Goa over last three years, dramatically illustrates the poor performance of the monsoons in Goa this year, as against 2013 and 2014.
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| Fig 7 |
The performance of the SW monsoons is in the deficient category on all India level too as per this map from IMD:
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| Fig 8 |
While IMD can take comfort from the fact that it had predicted the seasonal rainfall during 2015 to be +/- 88% of LPA with error of +/- 4%, in its Long Range Forecast update issued on June 2, 2015, the performance of the monsoons on the West Coast of India is one of the worst in recent times.
Meteorologists are attributing the deficient rains during SW Monsoons this year to the strong El Nino phenomenon that continues even as the SW monsoon season ends in India. We are going to hear a lot about the effect of El Nino in coming days, on the Monsoons in India this year.
The break in Monsoon in September saw significant rise in temperatures in the second half of September, as recorded at Panjim by IMD:
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| Fig 9a |
The highest day temperature of 34.8C and highest night temperature of 26.2C were both recorded on the last day of the month i.e. September 30
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| Fig 9b |
While comparison of SWM 2015 with other failed monsoon years like 2002, 2009, 2012 is inevitable, What stands out is the failure of the Arabian Sea branch of the monsoons in 2015, leading to deficient monsoon all along the west coast. The saving grace for SWM this year has been undoubtedly The Bay of Bengal Branch, bringing good rains to the east coast and to central India too!
The analysis of SWM 2015 will continue for a long time to come. Keep an eye on this blog for regular updates!
