A lopsided advance of the 2013 South West Monsoon over the Indian Subcontinent has helped to yield some highly unusual weather this week.
Isolated pre-Monsoon cloudbursts, some with damaging winds, hail and dust storms, have dealt out falls of rain sometimes amounting to many times the historical average amount for June in Pakistan and northwest India.
The onset of the Monsoon has taken place as far north and west as about Karachi, the India Meteorological Department (IMD) website showed on Thursday, June 13, 2013. Historically, South West Monsoon onset has not typically happened at Karachi before the second week of July.
At the same time, Summer Monsoon onset, as plotted by the IMD, has lagged several days behind the historical advance in the central Himalayas and eastern parts of the densely settled Ganges River basin. Most June rainfall as of the 13th has been insignificant to deficient, even where Monsoon onset has been declared by the IMD.
Pakistan and northwestern India have benefitted from the early Monsoon onset, which has coincided with significant Monsoon low pressure over the northern Arabian Sea.
Moist, rain-cooled air has broken the pre-Monsoon heat across the dusty plains, and some spots have received welcome soaking falls of rain.
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, according to the Pakistan Meteorological Department (PMD) website.
The hill town of Murree, Punjab, picked up 115 mm of rain in the two days ended Wednesday. Thus, most of the average June rainfall of 151 mm has already taken place.
In northern India, parts of Punjab and Haryana have already got the first heavy falls of rain two to three weeks ahead of the historical average Monsoon onset.
Enjoying the spray from high waves striking the coast at Mumbai, India, Thursday, June 13, 2013. Unbeknownst to most people other than mariners, strong southwesterly winds of the Indian Summer Monsoon were busily at work over the open Arabian Sea, as they would be each year in June, heaping up the high waves that eventually roll ashore on India's west coast. (AP Photo/Rafiq Maqbool)
--More Unusual Events Lie Ahead
To begin with, extreme, unseasonal rainfall that had earlier been indicated for Sindh and the Karachi area seems to have since been ruled out as atmospheric details become more clear. However, excessive pre-Monsoon rainfall and flood have remained a threat.
As the Arabian Sea low fades, a second Monsoon spinning northwestward over central India will bear watching. The immediate path of this low will provide a focus for flooding downpours through at least the first part of next week as it continues to track towards the northwest. The low will also trigger torrential rain in the western states of Gujarat and Maharashtra as it strengthens the onshore flow of the Monsoon southwesterlies.
Meanwhile, low pressure dipping southward over central Asia, a "western disturbance" to forecasters in the Subcontinent, will interact with the central India low. This interaction is likely to yield very heavy falls locally, especially along the Foothills of northern India, but even into Pakistan.
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!