வரும் ஆனால் வராது.

Last week Chennai and suburb experienced HOT and HUMID weather. Hot and Humid air was virtually hitting face at 10m high [top of three story building]. But Upper Tropospheric Humidity was concentrated very few pockets [as far as Chennai and suburb is concerned] and it experienced 30-90mm of rainfall all in total.  There was rain symptom but there were rains at pockets only.  [வரும்  ஆனால் வராது].  The spatial distribution of rain in Kerala and Karnataka is weak but temporal distribution (weak) nearing to negative side of Normal.  Statistical interpretation some times will lead to illusion.  

The threshold 850 hPa level moisture incursion is bleak. In atmosphere the moisture holding capacity will diminish aloft (or at higher level). But this time clouds were seen at height 3km. The total precipitable water at this level will be less in NON-CONVECTIVE clouds i.e SWM clouds so to say. 

The south Indian Ocean is warmer near Mauritius, where the usual STH will be forming.  However Bay branch of SWM is getting moisture to give copious rainfall in NE states like Assam,  Sripunji witnessed very  heavy rainfall, where as the SWM heavy rainfall gateway in western ghat region like Hulikal, Agumbe, Chinna Kallar witnessed very less rainfall. [If station level Normal and actual rainfall is considered for calculation it will be in deficient category only] 

Kerala and Karnataka as a whole, upto 02.09.2015, is deficient.  This is ground reality. But TN which is in the east is in Normal-negative side. Bay branch southerly winds helped. Here also evening radiation cooling saturated the unsaturated air and gave light rain.  some times local convection triggered thunder storm activity for 10-30min [10mm-60mm]