Tracking SW Monsoon Onset on the Subcontinent

Jul 5, 2011; 12:42 PM ET

SW MONSOON ONSET SLOW IN NW INDIA, NEIGHBORING PAKISTAN

Early onset of the SW Monsoon in western India (Mumbai by June 5, for instance), was followed by a near standstill that has lasted now for a full month, according to the India Meteorology Department (IMD). Thus, during the last four-plus months, the leading edge of the SW Monsoon has progressed only to central Gujarat, where it should have begun a good three weeks ago.

At the same time, monsoon onset has reversed from unusually slow in central and northeastern India to ahead of schedule in the middle north and the northwest.

Extrapolating the IMD tracking, monsoon onset has also extended into Punjab and other northern districts of Pakistan; again, this onset has taken place as much as one week ahead of the average onset date.

The pattern of fast onset on the west coast and slow onset farther east seems to have been shaped by the early June Arabian Sea tropical cyclone.

This pattern soon flipped as a deep monsoon low rolled ashore from the head of the Bay of Bengal, then barreled slowly west, flooding outbursts of rain and all, across mid-northern India. This coincided with the “catching up” with normal onset date by the SW Monsoon over the northern Subcontinent.

There has been a lull in the coverage of heavier falls of rain on the Subcontinent lately. Maybe, this qualifies as “break monsoon”. Anyways, there are indications in the numerical forecast models that the rain-making mechanism will crank up going forward into next week. Thus, the west coast, together with wide areas of the northeast and north, should see widespread, sometimes heavy, falls of rain.

At this time, there is no hint of any well-marked monsoon depression through at least early next week.

India Meteorology Department satellite image taken 1700 UTC July 5, 2011.