# Japan Weekly Weather Forecast API — Free JSON with High/Low Temps and Precipitation Probability

> Source: <https://dev.to/atu_ino_ed473db24d76d234a/japan-weekly-weather-forecast-api-free-json-with-highlow-temps-and-precipitation-probability-53ip>
> Published: 2026-10-12 12:02:38+00:00

If you want Japan's weekly weather forecast as JSON, the data is free and authoritative — it comes from the **Japan Meteorological Agency (JMA, 気象庁)**. The problem is the shape: the JMA publishes it as deeply nested JSON with parallel arrays, one file per prefecture (130000 for Tokyo, 270000 for Osaka…), and the field meanings are only documented in Japanese.

This post shows a free **MCP server** that normalizes it into a flat, predictable structure you can call from an AI agent or plain Python.

`sources` and reports failures in `data_gaps` instead of silently dropping them
Calling `japan_weekly_forecast(prefecture="東京都")` returns this (real output, trimmed):

```
{
  "retrieved_at": "2026-10-12T11:54:22+00:00",
  "sources": ["https://www.jma.go.jp/bosai/forecast/data/forecast/130000.json"],
  "data_gaps": [],
  "data": {
    "prefecture": "東京都",
    "area_code": "130000",
    "blocks": [
      {
        "time_defines": ["2026-10-13T00:00:00+09:00", "..."],
        "areas": [
          {"area": "東京地方", "weathers": ["くもり　時々　晴れ"]}
        ]
      },
      {
        "areas": [{"area": "東京地方", "pops": ["0", "0", "0", "10", "10"]}]
      },
      {
        "areas": [{"area": "東京", "temps": ["17", "25"]}]
      },
      {
        "areas": [
          {
            "area": "東京",
            "tempsMin": ["", "18", "18", "16", "15", "16", "18"],
            "tempsMax": ["", "27", "23", "24", "24", "24", "25"],
            "reliabilities": ["", "", "A", "A", "A", "A", "B"]
          }
        ]
      }
    ]
  }
}
```

The last block is the one most people want: **7 days of high/low temperatures plus a reliability grade (A/B/C)** so you can tell how much to trust day 6 and 7.

Three things the raw JMA feed makes painful:

`time_defines` do not line up 1:1. You have to join them yourself.`reliabilities` (信頼度) is an A/B/C grade most consumers never notice.
The wrapper preserves the block structure (so nothing is lost) but keeps each series keyed by `area`, which is what makes it joinable.

The server speaks MCP over stdio, so Claude Code, Cursor, or any MCP client can call it directly.

```
{
  "mcpServers": {
    "japan-intel-mcp": {
      "command": "japan-intel-mcp"
    }
  }
}
```

Then ask your agent something like *"what's the forecast for Tokyo this week?"* and it will call:

```
japan_weekly_forecast(prefecture="東京都")
```

Weather is one of eight read-only tools in the same server — all free, all keyless:

| Tool | What it returns | Source | 
|---|---|---|
| `japan_earthquakes` | Recent quakes: epicenter, magnitude, max intensity, depth | JMA | 
| `japan_weather_warnings` | Active warnings/advisories by prefecture | JMA | 
| `japan_weather_overview` | Narrative weather summary | JMA | 
| `japan_weekly_forecast` | 7-day high/low temps, precipitation %, reliability | JMA | 
| `japan_typhoons` | Active typhoon tracking | JMA | 
| `japan_edinet_filings` | Statutory corporate disclosures | EDINET | 
| `japan_postal_lookup` | Postal code → address (kanji and kana) | zipcloud | 
| `japan_watch_summary` | One-call cross-source summary | JMA | 

```
pip install -e .
japan-intel-mcp          # stdio mode
```

Source and releases: [github.com/atushi1841/japan-intel-mcp](https://github.com/atushi1841/japan-intel-mcp)

Also on the official MCP registry as `io.github.atushi1841/japan-intel-mcp`.

If you are building anything that needs current Japanese conditions — logistics, travel, event planning, or just an agent that should know it is typhoon season — this keeps you off scraped HTML.