Chiba Prefecture Rain Triggers Level 5 Flood-Inundation Alert as Record 110 mm/h Downpour Hits Funabashi

On Thursday, August 13, 2026, heavy rain in Chiba Prefecture from a line-shaped rainband (線状降水帯) swept across Chiba Prefecture east of Tokyo, producing record-breaking short-duration rainfall of about 110 millimeters (4.3 inches) in one hour in cities including Funabashi and Chiba City. The Japan Meteorological Agency (JMA) responded by issuing a Level 5 emergency heavy-rain warning for flood inundation (大雨特別警報・浸水害) — the highest alert on its five-tier scale — for 14 municipalities across northwestern Chiba, while local governments declared emergency safety instructions and Tokyo Electric Power (TEPCO) reported widespread blackouts affecting more than 11,000 homes.

Editor’s note: This article draws on JMA bulletins via the Choshi Local Meteorological Observatory, NHK WORLD-JAPAN, NTV, TBS NEWS DIG, TV Asahi (ANN), and TEPCO outage reports, August 13, 2026. Warning levels, evacuation orders, and power-restoration times can change rapidly; follow local authorities and the JMA’s Kikukuru app.

What a Level 5 emergency heavy-rain warning means

Japan’s disaster-weather system ranks heavy-rain alerts from Level 1 (early information) through Level 5 (emergency). A Level 5 emergency heavy-rain warning (大雨特別警報) is the maximum meteorological alert for rainfall. It signals that catastrophic flooding or river overflow is already highly likely — not merely possible — and that residents must take immediate life-protecting action.

Level	Alert type	What it signals
2	Heavy rain advisory (注意報)	Rising risk; monitor conditions
3	Heavy rain warning (警報)	Serious inundation risk in lowlands
4	Heavy rain danger warning (危険警報)	Life-threatening flooding; evacuate from danger zones
5	Emergency heavy-rain warning (特別警報)	Disasters likely already underway; seek maximum shelter now

The JMA issues Level 5 warnings as a benchmark for municipalities to declare emergency safety instructions (緊急安全確保) — the local-government equivalent of telling residents that staying put may be fatal and that they should move to the safest available location, even if that means sheltering on upper floors rather than traveling to an evacuation center.

Record rainfall: where and how much

Forecasters said the August 13 downpours were driven by a developing linear rainband — a narrow corridor of intense thunderstorm cells that can park over one area and dump extraordinary totals in minutes. JMA record short-duration heavy-rain advisories (記録的短時間大雨情報) were issued as observations and radar analysis confirmed extreme hourly rates:

Location / period	Estimated 1-hour rainfall
Funabashi (by ~5:20 p.m.)	~110 mm
Funabashi / Kashiwadai area (by ~7:30 p.m.)	~100 mm
Chiba City (by ~6:40 p.m.)	~110 mm
Chiba City Chuo Ward (by ~6:40 p.m.)	~110 mm

For context, 110 millimeters in one hour is roughly what central Tokyo averages across an entire month of August. When that volume falls in 60 minutes over already-saturated ground — Chiba had endured days of rain following Tropical Storm Chan-hom earlier in the week — drainage systems, rivers, and hillside soils can fail almost simultaneously.

NHK and commercial broadcasters showed street flooding, submerged underpasses, and overflowing roadside gutters across the prefecture’s northwestern commuter belt during the evening rush hour.

Municipalities under Level 5 and emergency safety orders

At 7:30 p.m. on August 13, the Choshi Local Meteorological Observatory — which issues weather bulletins for Chiba — announced a Level 5 emergency heavy-rain warning for 14 cities in northwestern Chiba:

Chiba City, Ichihara, Sakura, Yotsukaido, Shiroi, Ichikawa, Funabashi, Matsudo, Narashino, Kashiwa, Yachiyo, Kamagaya, Inzai, and Abiko.

Several municipalities simultaneously issued Level 5 emergency safety instructions (緊急安全確保), the strongest local evacuation signal:

Municipality	Notable action (evening of Aug. 13)
Chiba City	Emergency safety for Chuo, Hanamigawa, Inage, Wakaba, Midori, and Mihama wards
Funabashi	Emergency safety instruction issued ~8:27 p.m.
Ichikawa, Matsudo, Kamagaya, Narashino	Partial or citywide emergency safety orders
Noda, Nagareyama, Abiko, Urayasu	Level 4 heavy-rain danger warnings

TV Asahi reported that at least one woman was transported in cardiopulmonary arrest amid the flooding, though her condition and the precise circumstances were still being confirmed as of late-evening broadcasts.

The JMA warned that additional linear rainbands could form over southern Ibaraki and adjacent Kanto areas overnight, keeping the entire region on alert through the early hours of August 14.

Power outages across Chiba

Heavy rain, lightning, and wind brought significant electricity disruptions. TEPCO Power Grid reported that by roughly 8:06 p.m., about 11,680 homes across nine cities and towns in Chiba had lost power.

Area (approximate outages)	Homes affected
Chiba City Chuo Ward	~4,050
Yachiyo	~3,170
Matsudo	~1,780
Inzai	~1,150
Funabashi, Kamagaya, Ichihara	Hundreds each
Smaller municipalities	Tens of homes

TEPCO said restoration timelines remained uncertain for most areas as crews worked in dangerous conditions. Inzai and Funabashi were among the few municipalities given provisional estimates — roughly 9:50 p.m. and 9:20 p.m. respectively — though officials cautioned that timelines could slip if damage assessments revealed more extensive line failures.

Residents without power were advised to avoid candles near flooding, use battery-powered lights, and report downed lines to emergency services rather than approaching them.

Transport and travel disruptions

The rainfall coincided with Obon holiday travel and the evening commuter peak, amplifying disruption across Chiba’s dense rail network.

• Keisei Electric Railway suspended all trains on a 12-kilometer stretch of its Main Line between Keisei-Takasago and Keisei-Funabashi before resuming service around 5:15 p.m. — though Skyliner airport expresses and connecting lines continued reporting delays into the night.
• JR East and other operators issued rolling delay bulletins as crews inspected tracks, signals, and drainage near flooded sections.
• Road authorities warned against driving through ponding on expressways and underpasses, where as little as 30 centimeters of moving water can sweep a vehicle away.

Travelers heading to or from Narita International Airport — a major hub served by Keisei and JR lines through Chiba — were urged to check operator websites and allow extra time for alternative routing.

How this differs from broader Kanto warnings

Earlier on August 13, the JMA had issued Level 3 heavy-rain warnings across a wider Kanto footprint, including parts of Ibaraki, Saitama, and Tokyo, as Chan-hom’s remnant moisture fed scattered thunderstorms. Chiba’s evening escalation to Level 5 represented a distinct, localized catastrophe within that broader unstable pattern — concentrated along the prefecture’s northwestern urban corridor rather than a uniform regional alert.

Officials emphasized that warning levels are not interchangeable: a Level 3 advisory in one city does not convey the same urgency as a Level 5 emergency warning in a neighboring municipality sitting directly beneath a stationary rainband.

What authorities are telling residents

Throughout the evening of August 13, JMA forecasters and Chiba prefectural officials repeated several core messages:

• Do not wait for an evacuation order if you see or hear rapidly rising water, landslide rumbling, or flooding in your immediate area.
• Moving to an evacuation shelter may be dangerous once conditions deteriorate; if escape routes are flooded, relocate to upper floors of sturdy buildings away from cliffs and stream channels.
• Check municipal disaster portals and the Kikukuru app for ward-level instructions — Chiba City alone spans six wards with different risk profiles.
• Avoid basements, underground parking, and riverside paths until the rainband passes.
• Expect continued instability through the night of August 13–14 as additional convective bands may develop.

The JMA’s Choshi observatory said the atmosphere over Chiba remained highly unstable into late evening, with warm humid surface air colliding with cold upper-level air — a classic setup for repeat downbursts even after the initial 110 mm/hour cell moved through.

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Discussion

1. If you live in a Chiba commuter city, how do you decide when to leave versus shelter in place during a sudden downpour?

Japan’s system distinguishes between evacuation orders and emergency safety instructions that may tell you to stay put on higher floors. Where do you draw that line?

2. Power outages during flooding compound risk — no lights, no pumps, no phone charging. What does your household keep ready for a summer storm night like August 13?

Share what has worked — or what you wish you had — when trains stop and the grid goes dark at rush hour.

If you were in Funabashi, Chiba City, or along the Keisei corridor on August 13, tell us what you saw and how you got home safely.

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This article is news and general safety information, not personal emergency guidance. During active weather warnings, follow instructions from local authorities and the Japan Meteorological Agency.