RAINFALL SOMEWHAT BELOW NORMAL
Rainfall across India as a whole (and by extension, the Subcontinent) has been somewhat below normal since June 1, 2011, the official start of the Monsoon season.
Through Aug. 3, weighted average rainfall was 6 percent below normal, as reckoned by the India Meteorology Department (IMD). The districts with the greatest shortfall (at least 20 percent below normal) were in the northeast, the far north, and scattered across central India. Eastern Gujarat, Haryana and Assam/Meghalaya were found to have rainfall 33 to as much as 37 percent below normal.
Madhya Pradesh together with Konkan (western Maharashtra)/Goa were the wet districts with rainfall as much as 30 percent above normal.
For Pakistan, I do not have benefit of comprehensive rainfall analysis. However, a scan of data tables (Pakistan Meteorological Department) shows that parts of the country, foremost being Sindh, are short of rainfall; some are still awaiting the first meaningful downpour.
Karachi has had only 7.8 mm of rain since the start of June. This is only about 10 percent of what normally falls through August 10.
Much rainier Islamabad/Rawalpindi has had roughly normal rainfall, whereas Lahore has been significantly rainier than usual.
WHAT LIES BEHIND THE SHORTFALLS?
Short answer--I do not know. However, there has been a relative lack of well-marked monsoon lows, the kind that often spin westward from the northern Bay of Bengal.
As for the current period, there have been downpours over Sindh as well as neighboring western Gujarat, based on satellite imagery. Rain is observed at Karachi Airport even as I write.
I believe that the complex of downpours may hearken back to the tropical storm (Nock-Ten, or Juaning) that landed in northern Vietnam near the end of last month. The remnant wave of this storm should have tracked west, over northern Indochina to the Bay of Bengal and India.
Numerical model forecasts suggest at least scattered downpours in Sindh for another few days.
The plum rains are known as "meiyu" in China, the "baiyu" or "tsuyu" in Japan, and the "jangma" in the Koreas. The heart of the plum rain season stretches from early June to mid-July, with a tendency to shift south to north across the affected area.
In the wake of the mid-June cloudbursts, most of Pakistan to northwestern India last week saw a return to dry, hot weather typical of the weeks leading up to the Monsoon onset. It was as if the Monsoon withdrew to its "normal" position for the latter half of June.
The 38.5 degree C (101 degrees F) reading Tuesday in Ajaccio, Corsica, may have been tops in Europe.
Monsoon Onset was June 13th, 2013, in Delhi, almost two weeks earlier than average. The June 15th onset at Karachi and Islamabad was more like three week ahead of schedule.
In Pakistan, hit-or-miss downpours missed the Sindh capital, Karachi. One did hit Pad Idan, where it left 60 mm of rain Wednesday. This was more than 20 times greater than the normal June rainfall.
It is still possible that this scenario is over wrought as to the intensity and spread of rain in Pakistan and northwestern India. However, it is the hunch of the present forecaster that some very unusual weather is going to unfold in the Subcontinent during the next week!