Rainfall Nowcast (HKO)

Source

Hong Kong Observatory (HKO)

• Department URL: https://www.hko.gov.hk/
• API Endpoint: https://data.weather.gov.hk/weatherAPI/opendata/weather.php?dataType=rainfall&lang=en
• API Docs: https://www.hko.gov.hk/en/abouthko/opendata_intro.htm

Format

JSON Updated every 10 minutes. No API key required.

~10 min

Update Interval

~50

Rain Gauge Stations

mm/hr

Unit

Schema / Fields

Field	Type	Example	Description
data[].main	string	"Hong Kong Observatory"	District rain zone name
data[].place	string	"HKO"	Station identifier
data[].amount	float	12.4	Rainfall (mm) in past hour
data[].unit	string	"mm"	Measurement unit (always mm)
startTime	string	"2024-01-15T08:00:00+08:00"	Measurement period start
endTime	string	"2024-01-15T09:00:00+08:00"	Measurement period end

Rainfall Intensity Reference (HKO)

Amount (mm/hr)	Warning Level	Foot Traffic Impact
0	None	Normal
0–15	Amber Rainstorm	-20% outdoor diners
15–30	Red Rainstorm	-40% all foot traffic
30+	Black Rainstorm	-70% foot traffic

Example API Call

curl "https://data.weather.gov.hk/weatherAPI/opendata/weather.php?dataType=rainfall&lang=en" \
  | jq '.rainfall.data[] | select(.place == "HKO")'

Example Response

{
  "rainfall": {
    "data": [
      {
        "unit": "mm",
        "main": "Hong Kong Observatory",
        "place": "HKO",
        "amount": 12.4
      },
      {
        "unit": "mm",
        "main": "Central & Western District",
        "place": "CWB",
        "amount": 14.2
      }
    ],
    "startTime": "2024-01-15T08:00:00+08:00",
    "endTime": "2024-01-15T09:00:00+08:00"
  }
}

Used By

Model	How
ABM Theory	Rain amount → foot traffic multiplier: 0mm=1.0, 5mm=0.8, 15mm=0.6, 30mm+=0.3
LLM-Powered Agents	Rain state included in agent reasoning prompt as situational context

Notes / Gotchas

Tip

The Amber/Red/Black Rainstorm Warning system (from weather-current) is the cleaner signal for foot traffic — use the warning level rather than raw mm/hr for agent logic.

• amount field is 0 on dry days — defensive check before applying rain multiplier
• Rainfall is highly localized in HK due to topography — Sheung Wan can be dry while Sha Tin has a downpour
• This endpoint is the hourly accumulation — for instantaneous intensity, combine with the rhrread endpoint
• Combined data: fetch both rhrread and rainfall in a single pipeline run