Second storm in a week hits Japan but this time the winds are far weaker.

A week ago, Typhoon Lan made landfall on Japan’s main island of Honshu and was driven across Tokyo. It was a major typhoon, one of the biggest on record, but was weakening before it reached Japan’s capital.

Now another tropical cyclone is battering Japan. Saola is neither as large nor as powerful as its predecessor but has been around long enough to gather a lot of moisture and bring a landslide threat through its heavy rain.

On Friday, Saola passed over Okinawa. It was still a tropical storm, winds were no more than gale force. Many flights in and out of Okinawa’s airport were cancelled and in the city of Naha, 141mm of rain was recorded as Saola passed over.

Appearing to follow the Ryukyu archipelago of small Japanese islands, Saolo strengthened to become a typhoon – just barely. Wind strength is the factor that determines when a tropical storm becomes a typhoon, and Saola maintained this status for about 30 hours.

The real signature of Saola has been the amount of rain it was capable of dropping. Encountering Kyushu, it dumped an extraordinary 424mm in 24 hours on the cruise port of Aburatsu. This is a dangerous amount of rain to fall on a mountainous island such as Kyushu. Flash flooding and landslides are the usual result.

Travelling parallel with the Japanese coast, Saola soon dropped back to tropical storm status and, heading northeast, accelerated from 25 to 50 km/h – a remarkably fast-travelling tropical cyclone. Luckily for Honshu, including Tokyo, this makes the time of exposure to heavy rain much less.

It rained in Owase for 44 hours – the rain has always spread a long way in front of Saola – but in contrast to Aburatsu, Owase recorded a mere 136mm. Thirty-six hours of rain in Tokyo has yielded just 87mm.

Travelling away at some 50km/h, Saola had no chance of maintaining the characteristics of a tropical cyclone but will bring a spell of heavy rain to Hokkaido and the Kuril Islands on Monday. The Kamchatka Peninsula, then, will likely get a month’s worth of rain on Tuesday.