Tropical storm Nepartak is sitting off the east of Japan's largest island and is forecast to skirt along its east coast tonight before making landfall well north of Tokyo some time on Wednesday.
Earlier, the system was expected to cross the coast of Honshu today near Tokyo but has slowed and is now looking like making its way further north.
The Japan Meteorological Agency forecast is for the storm to maintain maximum wind speeds of 40 knots with gusts of 60 kt overnight before weakening as it makes landfall tomorrow.
Its current path suggests it will cross the coast near the city of Sendai, which has a population of more than a million residents and is 66km north-west of Fukushima and 370 kilometres from Tokyo.
Storm surge advisory warnings are out for coastal regions in the Miyagi and Fukushima prefectures.
But, as anyone who has waited anxiously for a cyclone will be aware, these systems can change direction and intensity quickly.
Tropical systems and typhoons are not an uncommon occurrence in a Japanese summer but, with all the world's eyes on the Olympics, this fairly typical tropical storm is getting a whole lot of attention.
How is it impacting the games?
Nepartak may currently be a relatively weak tropical storm but it is already bringing rainfall, strong winds and bigger surf.
The Olympic Games' surfing finals ? originally scheduled for tomorrow ? were moved to today.
Organisers have also made changes to the rowing program for tomorrow, Thursday and Friday, based on the forecast. Archery has also rescheduled events.
Games organisers are likely breathing a sigh of relief at the moment, but like the Games, the weather can go through many ebbs and flows in a fortnight.
What is a tropical storm?
Typhoons, tropical cyclones and hurricanes are all the same type of tropical storms generated over warm oceans.
How they are categorised and labeled, however, differs dramatically around the world.
Nepartak is currently categorised as a Tropical Storm (TS) in the International West Pacific Categorisation system and is not currently expected to strengthen to be a typhoon before it makes landfall.
Categorisation in Japan
International West Pacific Categorisation
Max wind speed* (knots)
Max wind speed* (meters per second)
- 33 kt
- 16 m/s
Sever Tropical Storm
Taifu (very strong)
Typhoon (very strong)
105 kt +
54 m/s +
*Sustained wind speeds, not gusts.
Comparing systems across basins is made difficult because of different recording practices and units.
But with maximum wind speeds of 40kt and gusts of 60kt (111km/hr) that puts it down as a category one cyclone in the Australian system.
Maximum mean winds* (knots)
Maximum mean winds* (kilometres per hour)
Maximum gusts (km/hr)
107 kt +
200 km/hr +
*Sustained winds, not gusts.
The US system is different again.
Neparak's current winds would mean it missed out on the cutoff to be a category one hurricane if it were on the other side of the Pacific.
Tropical systems are not the only ones that can generate strong winds.
Cape Leeuwin in Western Australia recorded a gust of 135km/hr as the west was battered by a cold front last night.
The main difference between Nepartak and a cyclone skirting along the Queensland coast is that it is spinning in the opposite direction.
Low-pressure systems spin clockwise in the southern hemisphere but counter clockwise north of the equator, thanks to the Coriolis effect.
© ABC 2021
15:18 AEST A low pressure system is generating a series of cold fronts that are likely to affect WA later this week.