The summer monsoon is a regular feature this time of year in India, and it can bring heavy rains to the region. However, periodically areas of low pressure can form within the general monsoon trough and bring even more rain.
Most of the Eastern half of the United States had rainfall during the past week. Some parts of the country experienced heavy rainfall that resulted in flash floods and various other problems. Slow-moving storm systems and nearly stationary fronts were the cause of heavy rainfall over Virginia this past weekend. Several trees were brought down by a severe storm that hit Fredericksburg, Virginia Sunday Afternoon. Fallen trees blocked several roads, flash flooding occurred and electrical power was lost in that area.
For close to two weeks the combination of a nearly stationary front and tropical moisture caused almost continuous precipitation over much of the Mid-Atlantic. Record amounts of rain fell over the eastern United States with over a foot of rain reported in some parts of the Mid-Atlantic. The excessive rain led to flooding along several rivers including the Potomac river.
Last week Tasmanian's were evacuated, businesses were flooded and cars washed away as extreme rainfall accompanied a strong cold front and a low pressure system that spawned violent storms. Hobart city, located in southeastern Tasmania, received record breaking rainfall of more than 100 mm (3.93 inches) in a single day. A strong pressure gradient developed between the complex low pressure center over Tasmania and high pressure that was moving eastward over the Great Australian Bight (Southern Ocean).
A low pressure trough moving slowly westward through the northwestern Hawaiian Islands caused destructive flooding and mudslides over the past weekend. The trough disrupted the normal northeast trade winds flow north of Oahu on April 12, 2018. This caused extremely heavy rainfall as the trough deepened and moved very slowly over Kauai during the weekend. The 28.1 inches (713 mm) of rain reported in Hanalei within a 24 hour period was close to a record for the small town on Kauai's northern coast. Almost 32.4 inches (822 mm) of rain was reported during the same period over Wainiha, Kauai.