Linear rainbands and heavy-rain warnings in Japan: what the 2026 changes mean
Japan's summer and autumn rains can be extreme, and since May 29, 2026, the Japan Meteorological Agency (JMA) has renamed and reorganized its heavy-rain information. This guide explains "linear rainbands" (線状降水帯), the new warning names, and what to do as a resident or visitor. JMA's English pages cover the warning names; for the rainband products, the English below is our translation.
What a linear rainband is
JMA describes a linear rainband as an area of intense rain stretching about 50 to 300 km long and 20 to 50 km wide (our translation). Because heavy rain keeps falling over the same place for hours, floods and landslides follow.
Three rainband products
| Product (our translation) | Timing | What JMA says |
|---|---|---|
| Half-day-ahead forecast | About 12 hours ahead | Heavy rain from a rainband is likely, but a rainband will not necessarily form |
| Imminent-formation bulletin | Within 3 hours | Hit rate about 50%; catches about 80% of rainbands in advance |
| Formation bulletin | When it forms | Issued when conditions are already at alert level 4 or higher |
New warning names
JMA now puts level numbers in warning names. In English, a "危険警報" is an "Urgent Warning": for example, "Level 4 Urgent Warning." JMA's English leaflet for foreign residents sums up the key message: "Evacuate by Level 4!" See "Japan's five alert levels explained."
Sudden downpours
JMA explains that a single thunderstorm cloud usually affects a small area for 30 minutes to an hour, but small rivers can rise within about ten minutes of the rain starting (our translation). In rain of 30 to 50 mm per hour, JMA warns that a film of water can form between tires and the road so brakes stop working.
What to do (our suggestions)
- Install a multilingual alert app before you travel, and learn where your hotel or home sits on the hazard map.
- If a half-day-ahead forecast is issued, prepare to leave while it's still light.
- Don't wait for the formation bulletin. Evacuate by Level 4.
- Never drive or walk into flooded roads or underpasses. See "Floods."
A Japanese version is available: "線状降水帯の情報" (in Japanese).
Everyday
If you live in or travel to Japan in the rainy season, check where your home or hotel sits on the local hazard map.
When it counts
Don't wait for a rainband to form. Evacuate by Level 4, and never enter flooded roads or underpasses.
Sources and when we checked them
- JMA, Information on linear rainbands (Japanese) (checked 2026-11-06)
- JMA, New disaster weather information from 2026 (Japanese) (checked 2026-11-06)
- JMA, English names of alert-level warnings (PDF) (checked 2026-11-06)
- JMA, Guide book: Staying safe during heavy rain disasters (PDF, English) (checked 2026-11-06)
- JMA, Rainfall intensity table (Japanese) (checked 2026-11-06)
- JMA, Protecting yourself from sudden heavy rain (Japanese) (checked 2026-11-06)
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