Weather API

The weather API (v5) serves station weather observations, rainfall, lightning, and typhoons for Taiwan, plus current weather from the nearest station and hourly township forecasts. The data comes from the Central Weather Administration (CWA), Ministry of Transportation and Communications. The server fetches it on a schedule and stores it as compact JSON. Every endpoint is GET, under the prefix /api/v5/meteor.

Data license

• Attribution · Commercial use OK

  AttributionData: Central Weather Administration (CWA), ExpTech Studio (exptech.dev)

Upstream terms

• Central Weather Administration (CWA): CWA's own data terms (such as the Open Government Data License) also apply; CWA's official releases take precedence.

Where to show it, examples and commercial-use requests: Data licensing and attribution.

Authentication

No API Token is required, and there is no extra access limit.

Datasets

Dataset	Page	Contents	Update	History kept
Station weather weather	Station weather	Temperature, humidity, pressure, wind, gusts, and the day’s high and low at automatic weather stations	About once an hour	3 days; trends up to 7 days
Current weather weather/realtime	Station weather	Current weather at the station nearest a coordinate	Checked every minute	Latest value only
Township forecast weather/forecast	Station weather	Hourly forecast for about the next 24 hours for a township	Every 15 minutes	Latest value only
Rainfall rain	Rainfall	Rainfall at rain gauges for each accumulation period	About every 10 minutes	3 days; trends up to 7 days
Lightning lightning	Lightning	Location and time of cloud-to-cloud and cloud-to-ground flashes	Checked every 30 seconds	3 days
Typhoons typhoon	Typhoons	Track, potential track, wind-radius strike probability, and typhoon warnings	Checked every minute	7 days, and at least the latest entry of each kind

“Checked every minute” means the server queries the source at that interval. A new entry is added only when the source has new data.

Servers and Base URL

The weather API is deployed only on the TNN-1 node, and the path decides which of two servers you call:

Path	Server	Cache
A snapshot whose path ends in a 10-digit Unix timestamp in seconds, for example /api/v5/meteor/weather/1794636000 or /api/v5/meteor/typhoon/track/1794636000	https://static.core-tnn1.exptech.dev	300 seconds (5 seconds for a 404)
Every other path: latest value, /list, /station, /trend/..., /realtime/..., /forecast/..., /typhoon/geojson	https://api.core-tnn1.exptech.dev	1 second

• The wrong server returns 404. api.core returns 404 for every timestamp-snapshot path. static.core serves only timestamp-snapshot paths.
• Do not use api.core.exptech.dev or static.core.exptech.dev, which DNS assigns to a node. On a node other than TNN-1, every weather path returns 404. Use the TNN-1 URLs in the table. The examples on each weather page use those two URLs.
• Legacy v3 (deprecated) is on https://tnn.exptech.dev. See Legacy v3.

Shared format

Endpoint shapes

weather, rain, lightning, and the four typhoon products all use the same shapes:

Shape	Path	Response
Latest	/api/v5/meteor/<dataset>	The latest snapshot
Time list	/api/v5/meteor/<dataset>/list	Snapshot times you can query, delta-encoded (see below)
One time	/api/v5/meteor/<dataset>/<10-digit Unix seconds>	The snapshot at that time, with the same structure as Latest. Only on static.core
Trend	/api/v5/meteor/<dataset>/trend/<station id>	A 24-hour or 7-day series for one station (weather, rainfall)
Station catalog	/api/v5/meteor/<dataset>/station	Station id to name, county or city, township, elevation, and coordinates (weather, rainfall)

A snapshot at a chosen time must use a time that appeared in /list. Any other time returns 404.

Columnar snapshots

Weather, rainfall, and lightning snapshots are arrays per field, aligned by index, rather than one object per station. For weather and rainfall, ids[i] looks up the station catalog for the name and coordinates. The catalog rarely changes. Fetch it once, then revalidate with the ETag.

const API = "https://api.core-tnn1.exptech.dev";

const [station, latest] = await Promise.all([
  fetch(`${API}/api/v5/meteor/weather/station`).then((r) => r.json()),
  fetch(`${API}/api/v5/meteor/weather`).then((r) => r.json()),
]);

const rows = latest.ids.map((id, i) => ({
  id,
  name: station[id]?.n,
  county: station[id]?.c,
  temp: latest.temp[i] === -99 ? null : latest.temp[i],
}));

Delta-encoded time lists

/list, and ts on a trend, are delta-encoded Unix seconds. The first element is the start time. Each later element is the gap, in seconds, from the previous time. Times run oldest first.

[1794632400, 3600, 3600]

That is the three times 1794632400, 1794636000, and 1794639600. Decode it like this:

function decodeDelta(a) {
  const out = [];
  let t = 0;
  for (let i = 0; i < a.length; i++) {
    t = i === 0 ? a[0] : t + a[i];
    out.push(t);
  }
  return out;
}

When there is no data, the response is [].

Time

• Times in v5 are Unix seconds (10 digits). <time> in the path is also seconds.
• Exception: updateTime on a township forecast is Unix milliseconds (13 digits). forecast[].time is a Taiwan-time "HH:00" string.
• time in legacy v3 is Unix milliseconds.

Units

Quantity	Unit
Air temperature, apparent temperature	°C
Relative humidity, probability of precipitation	%
Pressure	hPa
Wind speed, gust	m/s; typhoon movement speed is km/h
Wind direction	Degrees (station snapshots); a string (current weather, forecasts, typhoons)
Rainfall	mm
Distance, typhoon wind radius	km
Elevation	m
Coordinates	Decimal degrees, rounded to 4 decimal places

Weather, rainfall, and lightning use two fields, lat and lon. Typhoon geometry uses GeoJSON order [longitude, latitude].

Missing values

Data	How a missing value is written
Numeric fields on station weather, rainfall, and current weather	-99. Rainfall is never negative. Treat any negative value as no valid observation
gt, hit, and lot (times) on a station snapshot	0
Weather codes wx and weatherCode	0
Township forecast	Temperature, apparent temperature, and humidity are -99. Probability of precipitation, wind speed, and Beaufort number are 0. Wind direction is ""
Typhoons	null

Weather codes

wx on a station snapshot, and weatherCode on current weather and forecasts, use this three-digit code. The hundreds digit is cloud cover. The last two digits are an extra phenomenon.

Hundreds	Cloud cover
1	Clear
2	Cloudy
3	Overcast

Last two digits	Phenomenon	Last two digits	Phenomenon
00	No extra phenomenon, or no match	10	Ice pellets
01	Haze	11	Showers
02	Mist	12	Rain and snow showers
03	Lightning	13	Hail
04	Thunder	14	Thunderstorm
05	Fog	15	Thunder and snow
06	Rain	16	Thunder and hail
07	Rain and snow	17	Heavy thunderstorm
08	Heavy snow	18	Heavy thunder and hail
09	Snow grains	19	Thunder

For example, 206 is cloudy with rain. The code is 0 when the weather text does not start with clear, cloudy, or overcast, or when there is no data.

Caching and conditional requests

• Every v5 JSON response has an ETag (an MD5 in quotes). Send the previous value in If-None-Match. When the data is unchanged, the response is 304 with no body.
• Responses support gzip. Send Accept-Encoding: gzip (add --compressed to curl).
• Any origin may call cross-origin (Access-Control-Allow-Origin: *). A browser can fetch directly.
• Server-side cache: 1 second on api.core, 300 seconds on static.core.

Sources

Dataset	Source
Station weather, rainfall, lightning, typhoons	Open data from the Central Weather Administration, Ministry of Transportation and Communications
Current weather, township forecasts	Station observations and township forecasts on the CWA website

When you republish or display the data, credit the source with the suggested attribution in Data license.