Sunday, April 29, 2012

Traditional Heat Low

India, looking like an inverted triangle, is standing in the gate way for Indian Ocean (monsoon) winds. The max temp generated by GFS model indicates that eastern side of western ghat is warmer.  The intense land heating is just picked up in Indian landmass along with Bay just north of 13-14 Deg N latitude. As the Sun advances further to North more heating will take place and traditional heat low in NW parts of India will form.
Pluvial lakes formed in Thar desert during last three years SWM rain.  This lakes prevented heating in the NW.  It may be considered as one of the reasons for the delay of  formation or presence of  traditional HEAT LOW in the NW.
Lots of T.showers seen over S, N-E andhra, T.cells also seen over N,N-W Tamilnadu, Orissa ..
chennai - a super thunder shower seen over 20km North of Thiruvallur. 4:20pm

Official Monsoon forecast disappoints: The IMD plays safe, hedges its bet!

The long waited official forecast of the Indian Meteorological Department (IMD) was finally announced last Thursday evening. The country is set to receive normal South West Monsoon rains in 2012, for a third year in a row. “It is a normal forecast,” said Mr Vilasrao Deshmukh, Union Minister for Science and Technology.

A forecast of normal rainfall at 99% of LPA should be reassuring news for India where the monsoon is the lifeline of a farm-dependent economy. But as they say “The devil is in the details”. So what’s the fine print? These read as follows:

(a)  Southwest monsoon seasonal rainfall for the country as a whole is most likely to be Normal (96-104%) of Long Period Average (LPA)) with the probability of 47%. Quantitatively, monsoon season rainfall is likely to be 99% of the LPA with a model error of ± 5%. The LPA of the season rainfall over the country as a whole for the period 1951-2000 is 89 cm.

(b)  The probability (24%) of season rainfall to be below normal (90-96% of LPA) is also higher than its climatological value. 

(c)  However, the probability of season rainfall to be deficient (below 90% of LPA) or excess (above 110% of LPA) is relatively low (less than 10%).rainfall to be deficient (below 90% of LPA) or excess (above 110% of LPA) is relatively low (less than 10%).
The IMD’s forecast of a “Normal Monsoon” lacks a high confidence level as they preferred to actually hedge their bets. As the Business Standard noted - reading between the lines, two facts emerge: one that the probability of “normal” rains at 47 % is lower than around 51%, issued last year, and two, the likelihood of “below normal rains” at 24% is higher than that of 20% during 2011.