As typhoon Bualoi spins to the southeast at 115 miles per hour, a secondary non-tropical low can be seen organizing to the northwest. (RAMMB/CIRA/JMA)

Two weeks after Typhoon Hagibis killed more than 80 people in Japan with flooding and landslides, the same hard-hit areas on Honshu Island may experience dangerous flooding again, because of a heavy rain linked to Typhoon Bualoi. Significant rainfall is forecast to begin along the eastern coast of Honshu, which includes Tokyo, as early as Thursday.

Bualoi, which scraped the Northern Mariana Islands on Tuesday, currently has maximum sustained winds of 115 mph, making it the equivalent of a Category 3 storm as it churns well south and east of Japan. Both its strongest winds and heaviest rainfall are expected to remain offshore, passing several hundred miles to the east of Tokyo on Friday.

Light rain was already falling late Wednesday local time across much of Kyushu and was soon to overspread into Shikoku in southwestern Japan.

A rich stream of moisture from Bualoi will curl westward out of the storm, drawn into a nontropical low swirling up the spine of Japan and paralleling the typhoon. That will focus a band of heavy downpours that will ripple along Japan’s eastern shore.


The European model's simulation of a plume of moisture exiting Bualoi and becoming entrained in the non-tropical low to the west, setting the stage for very heavy downpours. (Weatherbell.com)

Uncertainty exists as to how close this band sets up relative to Japan’s coastline. Some computer models — such as the European — show the heaviest rain falling just to the east of Japan. Nevertheless, that model still shows more than half a foot of rain falling in spots that were hit hard during Hagibis, which set multiple rainfall records for the country.

Other models, such as the American GFS, aggressively bring the heaviest rain farther inland with isolated rain totals topping 10 inches in spots. The mountains, which act as a barrier to incoming moisture that can squeeze out copious amounts of rainfall, could receive far higher amounts.


A look at six-hour rainfall totals projected by the GFS shows a concentrated area of very heavy rain sweeping up Japan's east coast. (Weatherbell.com)

The most likely spot for these orographically induced higher totals is in the Akaishi and Kiso Mountains, especially in southern areas. Nearby Hakone, a few miles from Mount Fuji, received 37.1 inches during Hagibis, setting a record for that location and marking one of the highest calendar-day rainfall totals in Japanese history.

Particularly affected may be Chubu and Kanto, especially the Izu Peninsula — where Hagibis made landfall Oct. 12.

If heavy rain falls on steep terrain already loosened by Typhoon Hagibis, there will be renewed threats of dangerous landslides, as well.