A Typhoon Just Crossed Japan From East to West. Here Is Why That Almost Never Happens.
Typhoons in the western Pacific are supposed to come from the south. They form over warm water near the Philippines or the Marianas, drift northwest for a few days, and then, somewhere around the latitude of Okinawa or southern Japan, they turn right and run northeast. That right turn is so reliable that forecasters have a name for it. It is called recurvature, and most of the guidance you read about a storm is really an argument about where the turn will happen.
On Tuesday evening, Chan-hom did not do that. It came in from the Pacific and moved west, straight across the Kanto plain, in the wrong direction.
It made landfall in southern Ibaraki Prefecture at about 8 p.m. local time on 11 August, and the Japan Meteorological Agency noted something that is worth sitting with for a moment: this was the first typhoon landfall in Ibaraki since the agency started keeping that record in 1951. Seventy-five years of data, a coastline that faces the open Pacific, and it had never happened before.
Library image for illustration. It is not live satellite imagery of the storm discussed here.
Why storms normally turn right, and why this one did not
The reason typhoons recurve is that they are not self-steering. A tropical cyclone is essentially carried along by the air around it, the way a leaf is carried by a river. What matters is not what the storm wants to do but what the surrounding flow is doing.
In a normal western Pacific summer, that flow is dominated by a large area of high pressure sitting over the ocean, usually called the Pacific High. Air circulates clockwise around it. A storm approaching from the south sits on the western edge of that high, where the clockwise flow is pushing northwest. As the storm climbs north and reaches the top of the high, the flow it is sitting in swings around to the east. The storm turns with it. That is recurvature, and it is why Japan usually gets hit from the southwest and Korea usually gets whatever is left.
This week the high was in the wrong place. Instead of sitting to the south and east, a strong area of high pressure had stalled to the north of the Japanese archipelago. Chan-hom ended up on the southern flank of that block rather than the western edge of it, and on the southern flank of a clockwise circulation the wind blows from east to west.
So the storm went west. Not because it was unusual in itself, but because the room it was in had been rearranged.
This is the part that gets lost when a forecast is reduced to a red line on a map. The line is not a plan the storm has. It is a guess about where the surrounding air will be, and when the surrounding air does something rare, the line does something rare too.
How rare is rare
It is worth being precise here, because "unprecedented" gets used loosely in storm coverage.
Typhoons making landfall on the Pacific side of the Tohoku region are not unheard of, but they are close to it. Since 1951 there have been three: in 2016, in 2021, and in 2024. Three in seventy-five years, and all three of them in the last decade, which is its own uncomfortable observation.
Ibaraki, sitting just south of that stretch of coast, had zero. Chan-hom is the first.
That is a different kind of statistic from the ones that usually lead storm coverage. Wind speed records and rainfall records get broken somewhere every year, because there are a lot of places and a lot of categories. A first-ever landfall in a prefecture with seventy-five years of records is a statement about the track, not the strength, and tracks are the thing forecasters are least able to call far out.
Chan-hom was not a monster. At landfall its central pressure was around 980 hectopascals with maximum winds near 126 kilometres per hour. That is a real storm, enough to take down trees and stop trains, but it is not in the same conversation as Dolphin, which came ashore in Zhejiang two days earlier at 42 metres per second. If Chan-hom is remembered, it will be for where it went rather than how hard it hit.
What a backwards track actually changes on the ground
A storm moving east to west across Honshu distributes its weather differently from one moving southwest to northeast, and that has practical consequences.
The first is which side gets the wind. In a normal recurving typhoon passing to the west of Tokyo, the capital sits on the storm's eastern flank, where the storm's own rotation and its forward motion add together. That side is the dangerous semicircle, and it is why the same storm can be much worse in one prefecture than in the next one over. With Chan-hom coming in from the sea and heading inland to the west, the geometry flipped: the strongest onshore winds hit the Ibaraki and Chiba coasts first, and Tokyo, roughly 160 kilometres from the centre at the closest approach, got the weaker side.
The second is rainfall distribution. The JMA's forecast for the twenty-four hours through Wednesday evening was up to 180 millimetres in the Kanto-Koshin region, 150 in Tohoku, 120 in Tokai and 80 in Kinki. Read that sequence again and note the direction: the numbers step down as you move west, which is the storm handing its moisture off as it crosses the country and weakens.
The third is the tail. Crossing a mountainous island tears a tropical cyclone apart, and Chan-hom was expected to be a tropical depression by Wednesday afternoon, drifting out over the water off the Sanin coast. But a weakening storm is not a harmless one. The wind problem ends first and the water problem ends last, which is the same pattern China saw with Dolphin, where central Shanghai flooded on the Monday after the storm had already been downgraded.
Rivers in Kanto and Tohoku will be responding to Tuesday night's rain well into the rest of the week, on a day when the sky looks fine.
Where to check this yourself
This site is written after the fact and from a distance. For anything you are making a decision on, go to the agencies:
- JMA typhoon page (official, English): https://www.jma.go.jp/en/typh/
- JMA warnings and advisories by region: https://www.jma.go.jp/bosai/map.html
- JTWC warnings (official): https://www.metoc.navy.mil/jtwc/jtwc.html
- Japan Railways operating information: https://www.jreast.co.jp/e/
The thing worth taking away
Every so often a storm does something that the last seventy-five years of records say should not happen, and the explanation turns out to be boring. There was no exotic mechanism at work in Chan-hom. A ridge of high pressure parked in an unusual spot, the steering flow reversed, and the storm went the way it was pushed.
That is the useful lesson, and it is not a comforting one. The reason forecasts get track errors is not that the storms are unpredictable in themselves. It is that the environment they are travelling through can be arranged in configurations that have not shown up in the record before, and a forecast is only ever as good as its read on that environment.
So when you look at a cone and it seems to be pointing somewhere absurd, the useful question is not whether the storm would really do that. It is what the air around it is doing. Sometimes the absurd version is the one that verifies.
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