BOM weather warnings explained
A plain-English guide to Australia's warning system — what a Watch means versus a Warning, and how BOM grades cyclones, floods, fire weather and heat.
The Bureau of Meteorology (BOM) issues warnings when hazardous weather is likely to threaten life or property. They come in a tiered structure — Watches signal that a hazard is possible and you should prepare, while Warnings mean the hazard is occurring or imminent and you should act. Categories span severe weather, thunderstorms, tropical cyclones, floods, fire weather, heatwaves, damaging surf and tsunami.
Who issues warnings in Australia?
The Bureau of Meteorology (bom.gov.au) is the national authority for weather warnings. The Bureau forecasts the hazard and issues the warning; state and territory emergency services — the SES, and rural fire services such as the NSW RFS or CFA in Victoria — then translate that into advice and, where needed, evacuation orders through their own channels and the national Emergency Alert system.
This division matters. A BOM Severe Thunderstorm Warning tells you giant hail or destructive winds are coming; your state SES or the AFAC-run emergency apps tell you what to do about it. Always follow the emergency service, not just the meteorology.
What is the difference between a Watch and a Warning?
The distinction is timing and certainty, and it is the single most useful thing to understand about the whole system.
- Watch — conditions are favourable for a hazard to develop. It is a heads-up issued further ahead of time. A Flood Watch or a Tropical Cyclone Watch means "get ready".
- Warning — the hazard is expected, occurring, or imminent. It is issued closer to the event with higher confidence. This means "take action now".
For tropical cyclones the timing is explicit: the Bureau issues a Cyclone Watch when gales are expected within 48 hours, and upgrades to a Cyclone Warning when gales are expected within 24 hours.
What types of warnings does the Bureau issue?
| Warning | Hazard | Typical trigger |
|---|---|---|
| Severe Weather Warning | Damaging winds, heavy rain, abnormally high tides, damaging surf, blizzards | Widespread severe weather not from a thunderstorm or cyclone |
| Severe Thunderstorm Warning | Large hail, damaging/destructive wind gusts, heavy rain causing flash flooding, tornadoes | Thunderstorms meeting severe thresholds |
| Tropical Cyclone Watch / Warning | Gales, destructive winds, storm surge, flooding rain | Gales within 48 h (Watch) or 24 h (Warning) |
| Flood Watch / Warning | Riverine flooding graded Minor, Moderate or Major | Catchment rainfall and river gauge heights |
| Fire Weather Warning | Dangerous fire-weather conditions | Forecast fire danger at Extreme or Catastrophic (or state thresholds) |
| Heatwave Warning | Prolonged excessive heat | Low-intensity, Severe or Extreme heatwave categories |
| Marine Wind Warning | Strong Wind, Gale, Storm Force or Hurricane Force winds at sea | Wind-speed thresholds for coastal waters |
| Tsunami Warning | Marine threat or land inundation | Issued by the Joint Australian Tsunami Warning Centre |
How does BOM grade floods?
Australian flood warnings use three classifications tied to local river-gauge heights that the Bureau sets for each location, so "Major" on one river is a different height to "Major" on another:
- Minor flooding — causes inconvenience; low-lying areas and roads near watercourses are affected.
- Moderate flooding — low-lying land inundated, some buildings affected, main roads may cut, evacuation of some homes may be needed.
- Major flooding — extensive inundation, many properties and roads affected, isolation of towns likely.
The Bureau also separates slow-onset riverine flood warnings from flash flooding, which is usually flagged inside a Severe Thunderstorm or Severe Weather Warning because it develops in minutes rather than hours.
How does the heatwave service work?
The Bureau's heatwave assessment is relative to what is normal for each location, because a 38°C day is routine in Marble Bar but dangerous in Hobart. It grades heatwaves into three levels — low-intensity (common, most people cope), severe (challenging for vulnerable people such as the elderly), and extreme (dangerous for anyone who does not take precautions, and for those working outdoors). Heatwaves are Australia's deadliest natural hazard by long-term toll, which is why the service exists.
How does checkweather fit in?
An official warning tells you a hazard is coming; it does not tell you how confident the underlying forecast is. That is where checkweather's model comparison adds context. When the three global heavyweights — ECMWF (European), NOAA's GFS (American) and DWD's ICON (German) — agree on a system's track and rainfall, the forecast confidence score is high and a Watch is likely to firm into a Warning. When they diverge, expect the situation to shift. We always link straight through to the Bureau for the official warning, because BOM is the legal authority; we add the plain-English confidence layer around it. No black boxes.
What should you do when a warning is issued?
A warning is only useful if it changes your behaviour, and the right action depends on the hazard. A few general principles hold across all of them:
- Know your triggers in advance. Decide before the season what conditions will make you leave, move the car, or bring in loose items. In the moment, adrenaline is a poor planner.
- Match the action to the hazard. Severe thunderstorm with giant hail means shelter vehicles and stay indoors away from windows; a Major Flood Warning means move to higher ground early and never drive through floodwater; a Fire Weather Warning on a Catastrophic day means leaving bushfire areas is the safest option.
- Keep more than one channel open. Warnings escalate quickly. Pair the Bureau's page with your state emergency-service app, local radio (ABC Local Radio is the official emergency broadcaster in many areas), and phone alerts.
Above all, treat the upgrade from Watch to Warning as your cue to stop preparing and start acting. The window between the two exists precisely so you are not caught out.
How often are warnings updated?
Warnings are living documents. The Bureau reissues them as a system evolves — a Severe Thunderstorm Warning may be updated every hour or more as cells build and decay, while tropical cyclone advices follow a set schedule that tightens as the storm nears the coast. Each reissue carries a time stamp and a "next issue" time, so you always know whether you are looking at current information or a lapsed notice. If a warning is cancelled, the Bureau says so explicitly rather than letting it quietly expire, which is your signal that the immediate threat has passed.
Where do I find live warnings?
Go to the Bureau's national warnings summary at bom.gov.au/australia/warnings, or your state's page. During major events, pair it with your state emergency service's app and the national Emergency Alert (which can send warnings to your phone based on location). Register for the Bureau's warning notifications where offered, and never rely on a single source during a fast-moving event.