Japan issued its top landslide warning for Niijima as record rain lashed Tokyo’s islands

A stretch of the Izu Islands south of Tokyo was hit with rainfall heavy enough to break decades-old records, prompting Japanese authorities to issue their most severe landslide alert. The warning, reserved for situations where a landslide is considered an imminent, life-threatening risk, went out for the village of Niijima as rain intensified over several island communities. The scale of the rainfall, not just the warning level itself, is what set the event apart from routine seasonal storms in the region.

A Level 5 Warning Reserved for Imminent Danger

Japan’s Meteorological Agency issued Level 5 emergency landslide warnings for Niijima, along with the town of Oshima and the village of Toshima. Japan’s warning system reserves its top tier for conditions where a hazardous event, in this case a landslide, is judged to already be occurring or unavoidable, rather than merely possible, which places a Level 5 alert well above the kind of advisory that simply tells residents to stay cautious. Reaching that threshold across three separate island communities in a single event underscores how widespread the rainfall was across the chain.

The warning tier, detailed in reporting from The Watchers, sits atop a five-level system Japan uses nationwide to communicate escalating disaster risk, with each step up intended to trigger a different level of response, from general caution at the lower levels to evacuation at the top. Because Level 5 is meant to indicate a hazard is already underway or effectively certain rather than merely likely, its issuance functions less as a forecast and more as a real-time signal that conditions on the ground had already crossed into dangerous territory by the time authorities announced it.

Rainfall That Broke a Five-Year-Old Record

The rain that triggered the warnings was extreme by the islands’ own historical standards. Niijima recorded 485 millimeters of rain in the 24 hours leading up to 9:40 a.m., surpassing the location’s previous all-time record of 333.5 millimeters, which had stood since July 2021. Nearby Izu Oshima logged an even higher total, 581.5 millimeters over the 24 hours ending at 2:30 p.m. the same day. Totals of that size, arriving within a single day, are the kind of rainfall event that overwhelms drainage and saturates hillsides far beyond what the islands’ terrain is built to handle.

Breaking a record that had itself been set only five years earlier, in July 2021, adds context to how unusual the September 2026 totals were: the previous benchmark was not an ancient, rarely challenged figure but a comparatively recent extreme that this storm still surpassed by more than 150 millimeters. Small volcanic islands like those in the Izu chain tend to have steep terrain and thin soil cover, conditions that translate heavy rainfall into landslide risk more readily than the gentler, better-drained topography found in many mainland areas.

Typhoon Krovanh’s Moisture Fed the Frontal System

The storm’s intensity traced back to a broader weather pattern rather than an isolated local downpour. Warm, moist air associated with Typhoon Krovanh, the twenty-fourth named typhoon of the season, moving near Minamidaitojima in Okinawa prefecture, fed into a stationary frontal system positioned over the Tokyo region, intensifying the rainfall it produced. That combination, a typhoon supplying moisture to a front rather than making direct landfall itself, is a recognized mechanism for producing extreme localized rain totals well outside the typhoon’s own immediate track.

Typhoon Krovanh itself stayed well to the south, near Minamidaitojima in Okinawa, meaning the Izu Islands and Tokyo region never experienced the storm’s core winds directly. The damage instead came entirely from the moisture it pumped into an already-stationary front, a reminder that a typhoon’s most disruptive effects on a distant region can arrive as rainfall rather than as the wind and storm surge more commonly associated with a direct hit.

The Toll Reported Near Tokyo

Beyond the landslide warnings themselves, the record rain was linked to at least one death near the Tokyo region, underscoring that the danger from this kind of event extends beyond the specific islands placed under the highest alert. Flooding and heavy rain also affected Kanto-region prefectures surrounding Tokyo more broadly, reflecting how a single frontal system enhanced by typhoon moisture can produce hazardous conditions across a wide geographic area rather than one isolated location.

For the Izu Island communities directly under the Level 5 warning, the event illustrates how quickly a seasonal rain system can escalate into the most serious category of landslide risk Japan’s warning framework has, particularly on islands where steep terrain and saturated soil leave little buffer once rainfall totals cross a critical threshold.

The gap between the previous record and the new one, more than 150 millimeters in a location that had already logged its heaviest rainfall on record just five years earlier, also raises a longer-running question about whether the region’s rainfall extremes are shifting rather than simply producing one unusual outlier year. A single storm cannot answer that question on its own, but the recurrence of record-breaking rainfall within a relatively short span keeps the islands’ vulnerability to landslide-triggering downpours squarely on the list of hazards local authorities have to plan around each rainy season.

This article was produced with AI assistance and edited by Morning Overview staff.

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