April has been a soaking wet month already across Japan, with almost a whole month's worth of precipitation in only 2 days time.
A storm on the 2nd and 3rd brought torrential rains to major cities in Japan. In the Kanto Plain, cities were inundated with rain.
The hardest hit location was the Japanese Capital in Tokyo, which received over 4.48 inches (11.4 cm) of rain earlier this month. For Tokyo, this mean the city has already received 85 percent of its normal precipitation, For just the first 5 days of the month, 4.48 inches would convert to 507 percent of the normal precipitation.
Another city further north on the Kanto Plain that was hard hit was Sendai, which received 1.65 inches (4.2 cm) of rain during the event, almost half the normal amount they see during the month of April on average.
The result of such heavy rains has been flooding for many locations in the Kanto Plain. Flood warnings are in effect as many of the region rivers have reached flood stage.
During the rain event itself, low lying areas and those places with poor drainage saw groundwater pile up. A subway system in Tokyo was flooded.
While Tokyo does have a system of tunnels designed to assist in flood prevention, the system was not enough to prevent flooding from occurring.
More rain is expected on Saturday night and Sunday as well. Many of the computer models are currently predicting a storm system that should lift over central Honshu during that time period to bring anywhere between 0.75 and 1.50 inches (2-4 cm) of rain to most locations, with locally higher amounts.
Looking forward, the combination of additional rainfall and an already saturated ground could lead to more than just localized flooding. Rivers already in flood stage may see conditions worsen.
Another threat will be from landslides, as the ground continues to saturate and eventually give way, especially in hillier locations. Landslides always carry the potential to bring significant damage as they sweep large chunks of land downhill, destroying entire homes in their path.