A shot of heavy rain will threaten flooding along the east coast and eastern slopes of Australia, including greater Sydney, Thursday to Saturday.
Official Flood Watches have been posted by the Bureau of Meteorology (BoM) as of Wednesday, local time, for eastern drainage basins of New South Wales, between the Queensland border and the Hunter Valley, the BoM website showed.
Rainfall will commonly reach 125 mm (5 inches) but will top 25 cm (10 inches) in a few places. Isolated 50-cm falls will even be possible along east-facing slopes.
The heavy rain will begin Thursday in northeastern New South Wales. Spreading southward, it will pelt greater Sydney Friday into Saturday.
The trigger for the cloudbursts will be subtropical low pressure, hovering offshore as of midweek. This low, which already dumped flooding rain over southeastern Queensland early in the week, will turn back to the New South Wales coast on Friday.
Subtropical low pressure has pulled away from the east coast of Australia as of Wednesday, Feb. 20, 2013. This low is forecast to turn back to the west, landing in New South Wales on Friday. (Image: Bureau of Meteorology)
The at-risk corridor will overlap areas hard-hit by extreme rainfall and near-record flooding late in January. These rains followed the landfall of Tropical Cyclone Oswald on the Cape York Peninsula of northern Queensland. Oswald then drifted southward near the east coast, spreading high winds, extreme rainfall and major flooding as far south as the Sydney area.
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!