Southwest Monsoon Forecast 2015 – Who is Right?

The last two days has seen intense debate on the latest Southwest Monsoon Forecast 2015 put out by IMD.  IMD has warned this year’s Southwest Monsoon could be as low as 88% of Long term Average which effectively means we are staring at a potential second successive drought.  Compare this against the stand taken by India’s only Private Weather Forecaster, SkyMet, who are sticking to their original forecast of 102%  Rainfall of Long Term Average. So Who is Right?

COMK is  no where a professional body to put out its own forecast or possibly comment who is right and who is not.  But we are passionate enough to do our own analysis and present our views.

IMD has based its expectations on two factors, a possibly strong El Nino during the SWM period & Indian Ocean not evolving enough to bring a strong Positive IOD to negate the effects of El Nino. IMD’s own Multi Model Forecast expects a 90% probability of El Nino  & 50% probability of Neutral IOD during Southwest Monsoon.

http://www.imd.gov.in/section/nhac/dynamic/eng_lrf2.pdf

SkyMet is betting on one important factor – Back to Back droughts are a rarity and have given the years of 1904-05, 1965-66 & 1985-87 as the only instances of successive droughts in about 100 years, a statistical probability of 3%.  Another factor in their assessment is the evolution of Positive IOD in time for SWM.  They quote 1997 a year of strong El Nino with an equally strong Positive IOD that resulted in a normal year.

http://www.skymetweather.com/content/weather-news-and-analysis/ceos-take-why-skymet-is-sticking-to-a-normal-monsoon-in-2015/

So who is going to get right? Time only can answer.

In the meanwhile  some dope from our side.  The first table is a compilation of the yeas when El Nino had set in by April like the current year. Of these years, 1983, 1992 & 1993 saw El Nino end before the onset of SWM (Please click on the table for a larger image to get better understanding)

As one can see in the two tables attached below 1997 was seriously an exceptional year where in despite a very strong El Nino SWM performed very well.  Almost all the other years where positive IOD has been around during SWM it has not been able to negate El Nino by much with the best year seeing 15% meteorological divisions suffering deficit rainfall and the worst year seeing 69% meteorological divisions receive deficit rainfall.  A Swallow does not make a Summer. Can we make our forecast based on the year 1997.

Slide1

 

The second table is a compilation of years when El Nino set in by the time SWM onset happened.  The years 1963, 2004 & 2009 saw El Nino set in along with the onset of SWM and the rest of the years were a carry forward of El Nino from the Indian Winter. The year 2009 stands out in this table, the worst year with 77% of meteorological divisions receiving less than 90% rainfall.  The conditions that prevailed during SWM was El Nino & Neutral IOD, very similar to what is expected by most models for the year 2015.

Slide2

As you can see in both the tables it is pretty obvious under Strong El Nino Conditions irrespective of prevailing IOD conditions more often than not at least 50% of the meteorological divisions have faced less than 90% rainfall.  So what is COMK’s take – As things stand 2015 could end up a deficit year.