Hong Kong — Polymarket Weather Trading Reference

Overview

Hong Kong is a priority city for the Poly Weather bot. The Hong Kong Observatory (HKO) is the official settlement source for Polymarket Hong Kong temperature markets, making HKO data uniquely valuable — it's both the forecast provider and the ground truth.

City slug: hong_kong
Temperature unit: °C
Timezone: Asia/Hong_Kong (UTC+8)
Polymarket URL pattern: https://polymarket.com/event/highest-temperature-in-hong-kong-on-{month}-{day}-{year}
Dashboard page: /cities/hong-kong

HKO Open Data API

Base URL: https://data.weather.gov.hk/weatherAPI/opendata

No API key required. No documented rate limits. Free and open.

1. 1-Minute Temperature CSV (Primary — 0.1°C precision)

Endpoint: GET https://data.weather.gov.hk/weatherAPI/hko_data/regional-weather/latest_1min_temperature.csv

Returns real-time readings from 30+ automatic weather stations with 0.1°C precision, updated every minute.

CSV format:

Date time,Automatic Weather Station,Air Temperature(degree Celsius)
202603191730,HK Observatory,26.4
202603191730,King's Park,25.8
202603191730,Sha Tin,26.8
202603191730,Tai Mo Shan,18.2

Reference station: "HK Observatory" (尖沙咀天文台總部) — this is the station used for official temperature records and Polymarket settlement.

Notes:

Some stations may report N/A when sensors are offline
Includes additional stations not in the JSON API (e.g. Ngong Ping, Tai Mo Shan, The Peak, Tate's Cairn)
Updates every 1 minute (much faster than the JSON API's ~10 min interval)

2. Current Observations JSON (Fallback — integer precision)

Endpoint: GET /weather.php?dataType=rhrread&lang=en

Returns real-time readings from 26 monitoring stations across Hong Kong, updated approximately every 10 minutes. Integer precision only (e.g. 27°C instead of 26.4°C).

Key response fields:

{
  "temperature": {
    "data": [
      { "place": "Hong Kong Observatory", "value": 27, "unit": "C" },
      { "place": "King's Park", "value": 26, "unit": "C" }
    ],
    "recordTime": "2026-03-19T17:00:00+08:00"
  },
  "humidity": {
    "data": [{ "place": "Hong Kong Observatory", "value": 58 }],
    "recordTime": "2026-03-19T17:00:00+08:00"
  }
}

Note: Station names differ between CSV and JSON (e.g. "HK Observatory" in CSV vs "Hong Kong Observatory" in JSON).

2. 9-Day Forecast (fnd)

Endpoint: GET /weather.php?dataType=fnd&lang=en

Returns daily max/min temperature forecasts for the next 9 days. Updated ~4 times daily (around 00:00, 06:00, 12:00, 18:00 HKT).

Key response fields:

{
  "updateTime": "2026-03-19T16:30:00+08:00",
  "weatherForecast": [
    {
      "forecastDate": "20260320",
      "week": "Friday",
      "forecastMaxtemp": { "value": 28, "unit": "C" },
      "forecastMintemp": { "value": 23, "unit": "C" },
      "forecastMaxrh": { "value": 85, "unit": "percent" },
      "forecastMinrh": { "value": 60, "unit": "percent" },
      "ForecastIcon": 51,
      "forecastWeather": "Mainly fine. Hot during the day.",
      "forecastWind": "South force 3 to 4.",
      "forecastDate": "20260320"
    },
    ...
  ]
}

3. Other Useful Endpoints

dataType	Description	Use Case
`flw`	Local Weather Forecast (text)	General outlook
`warningInfo`	Weather Warnings	Extreme conditions
`sundata`	Sunrise/Sunset times	Daytime determination

Ensemble Model Integration

HKO is one of 4 models in the ensemble probability calculation:

Model	Weight	Source	Coverage
ECMWF	30%	Open-Meteo	Global
GFS	25%	Open-Meteo	Global
HKO	25%	HKO API	Hong Kong only
ICON	20%	Open-Meteo	Global

For non-Hong Kong cities, HKO is excluded and remaining weights are re-normalized.

HKO has lower standard errors than other models for Hong Kong forecasts:

Lead Time	HKO σ	GFS σ	ECMWF σ	ICON σ
24h	0.8°C	1.2°C	1.0°C	1.3°C
48h	1.0°C	1.5°C	1.3°C	1.6°C
72h	1.2°C	1.8°C	1.5°C	1.9°C

Strategy Considerations for Hong Kong

OBSERVED_YES / OBSERVED_NO

These strategies are especially effective for Hong Kong because:

HKO updates every ~hour — faster than market repricing
HKO is the settlement source — no discrepancy between observation and settlement
Peak hours 11:00–14:00 HKT — best window for OBSERVED_YES signals
Daily high usually occurs 13:00–15:00 HKT — after peak, OBSERVED_NO confidence is highest

TAIL_NO

Hong Kong temperature distribution is narrow (maritime subtropical climate), so tail buckets (e.g. "32°C or higher" in winter) are often overpriced by the market.

LATENCY_ARB

HKO forecast updates at ~00:00, 06:00, 12:00, 18:00 HKT. The 06:00 and 12:00 updates are most likely to shift probabilities, creating latency arbitrage windows.

Settlement Rules

Market question: "Will the high temperature in Hong Kong be X°C on [date]?"
Settlement source: Hong Kong Observatory official daily maximum temperature
Settlement time: After midnight HKT on the market date (once daily max is finalized)
The daily max is typically recorded between 13:00–15:00 HKT

Key File Paths

Weather Engine (backend)

packages/weather-engine/src/providers/hko-api.ts — HKO provider (fetch + fetchCurrentMax)
packages/weather-engine/src/providers/open-meteo.ts — fetchAllModels() conditionally includes HKO for HK
packages/weather-engine/src/ensemble.ts — Ensemble weights and probability calculation

Dashboard (frontend)

packages/dashboard/src/app/cities/hong-kong/page.tsx — HK page server component
packages/dashboard/src/app/cities/hong-kong/HongKongClient.tsx — HK page client component
packages/dashboard/src/app/api/hko-current/route.ts — HKO real-time temperature API
packages/dashboard/src/app/api/hko-forecast/route.ts — HKO 9-day forecast API

Core

packages/core/src/constants.ts — City config (lat/lon, timezone, priority)
packages/core/prisma/schema.prisma — Database schema

HKO Weather History (for verification)

Official daily extract: https://www.weather.gov.hk/en/cis/dailyExtract.htm?y={year}&m={month}

Use this to verify settlement temperatures and backtest strategy performance.

HONG_KONG.md 6.4 KB History Raw