Reviews
Hazard measures and public safety products compared
Hazard measures compared across earthquake magnitude and intensity, storm tracks and impacts, forecast probability, observations, watches, and warnings.
What to take away
- A physical hazard measure is not the same as local impact.
- Forecast track does not define the full hazard area.
- Probability does not state severity unless the product says what outcome is counted.
- Alerts describe decisions under an issuing system, not a universal danger scale.
- Early values may be revised as more observations arrive.
News alerts often compress a complex hazard into one number, line, or label. That shortcut fails when the measure answers a narrower question than readers assume. USGS ShakeMap, the National Hurricane Center track forecast cone, and a Storm Prediction Center convective outlook are three public safety products that each answer a different question.
These comparisons show what each field and product can support and what it leaves unresolved. The weather and public safety reporting guide puts these fields into the full story workflow.
Earthquake magnitude and intensity
| Field | Meaning |
|---|---|
| Magnitude (moment magnitude) | Size of an earthquake at its source under a magnitude scale |
| Intensity (Modified Mercalli Intensity) | Shaking and effects at a particular location |
| Depth | Distance below the surface associated with the earthquake location |
| Epicenter | Point at the surface above the earthquake's location |
One earthquake has one magnitude under a particular calculation, while shaking intensity varies by place. The USGS overview of magnitude, energy release, and shaking intensity says an earthquake has a single magnitude, determined from seismometer records. The shaking it causes takes many values that vary with distance, surface material, and other factors.
Magnitude vs. Intensity
Magnitude
- What it measures
- Size at source
- Number of values
- One per quake
- How determined
- Seismometer records
- Use for damage
- Not alone
Intensity
- What it measures
- Shaking at location
- Number of values
- Many per quake
- How determined
- Distance, surface, factors
- Use for damage
- Local effects
The Modified Mercalli Intensity scale runs from I, not felt, to XII, total damage. Japan's Meteorological Agency uses a separate shindo scale from 0 to 7, with 5 and 6 split into lower and upper readings.
USGS ShakeMap turns seismometer readings into a shaking map within minutes of an event. USGS PAGER adds estimated fatalities and economic losses, flagged green through red. ShakeAlert, the West Coast early warning system, pushes alerts to California, Oregon, and Washington phones through Wireless Emergency Alerts and partner apps.
Do not infer neighborhood damage from magnitude alone. Ground conditions, distance, depth, construction, and other factors shape local effects.
Tropical cyclone center track and hazards
What it represents
- Forecast point (NHC Forecast/Advisory)
- Predicted center position at a time
- Track forecast cone
- Area based on historical center-track errors
- Wind field (Wind Speed Probability graphic)
- Forecast or analyzed wind extent
- Watch and warning areas (storm surge, hurricane, tropical storm)
- Place covered by an official product
What it does not represent
- Forecast point (NHC Forecast/Advisory)
- Exact future location
- Track forecast cone
- Boundary of wind, rain, surge, or tornado risk
- Wind field (Wind Speed Probability graphic)
- All hazards from the cyclone
- Watch and warning areas (storm surge, hurricane, tropical storm)
- Forecast track confidence by itself
Before reading the cone, confirm the advisory time and forecast cycle. Compare it with current watches, warnings, wind fields, rainfall forecasts, and storm-surge products. A center point can shift between advisories while hazardous weather reaches far beyond it. Never infer a local evacuation instruction from track geometry alone.
Track Cone vs. Hazards
Track cone
- Shows
- Forecast center
- Does not show
- Storm size
- Check
- Advisory time
- Local action
- Not evacuation
Hazard products
- Shows
- Wind, rain, surge
- Does not show
- All hazards
- Check
- Watches, warnings
- Local action
- Official orders
The National Hurricane Center's descriptions of its graphical products explain that the track forecast cone graphic depicts the forecast of the center of the cyclone. It shows the current center position, forecast positions at stated times, and separately shaded coastal watch and warning areas. The cone is not a storm-size diagram. Hazardous conditions can occur outside it.
The Saffir-Simpson Hurricane Wind Scale rates storms 1 to 5 on peak sustained wind. Category 1 starts at 74 mph and Category 5 at 157 mph. The scale covers wind only, not surge, rain, or tornadoes. The NHC issues a separate Storm Surge Watch and Warning graphic, introduced in 2017, for inundation that threatens life.
Probability, amount, and threshold
A probability must name an event. "A 30 percent chance" is incomplete without the place, period, and threshold. Expected rainfall is an amount. The chance of exceeding two inches is a threshold probability. A high-end scenario is neither the most likely result nor an automatic warning.
The Storm Prediction Center's Day 1 Convective Outlook labels risk as marginal, slight, enhanced, moderate, or high. Its probability lines state the chance of severe weather within 25 miles of a point.
Weather Prediction Center quantitative precipitation forecasts give expected amounts. Probabilistic versions give the chance of exceeding 1, 2, or 3 inches. Use the legend's units and definition, and never estimate a value by color when a table or point readout exists.
Economic measures repay the same skepticism; major economic indicators compared keeps their questions apart.
Observation, estimate, and forecast
- Observationa sensor or person records a condition at a place and time. Automated Surface Observing System stations, USGS streamgages, and CoCoRaHS volunteers all report this way.
- Estimatea method derives a value from measurements or models.
- Analysisobservations and methods are combined to describe current or past conditions.
- Forecastexpected future conditions under a stated system.
Each can be revised. A preliminary earthquake magnitude, storm total, peak wind, and casualty count may change for different reasons. State the revision rather than hiding it.
USGS "Did You Feel It?" reports sit in the estimate column, because residents describe shaking after the fact. Health evidence carries parallel labels; the comparison of health evidence and alert types keeps signals, studies, and messages apart.
Watch, warning, and local order
A meteorological watch or warning is not the same as an evacuation order. The Storm Prediction Center issues tornado and severe thunderstorm watches for broad areas. Local National Weather Service offices issue tornado and flash flood warnings for specific counties. Wireless Emergency Alerts push a shortened version, capped at 360 characters, to phones.
Different authorities can issue products for different purposes. Report who made the decision, which area it covers, when it takes effect, and what action it requires. Reading a single product end to end is covered in how to read a weather alert.
Common questions
Can two places have different earthquake intensity from one event?
Yes. Intensity describes local shaking and effects, while magnitude describes earthquake size at the source.
Is every location inside a hurricane cone expected to be hit by the center?
No. The cone represents a probable center-track area based on historical forecast errors.
Does a higher probability mean a more severe event?
Not necessarily. Probability and severity are separate unless the product defines a probability of a specific severe threshold.
Is an evacuation order a weather forecast?
No. It is a public-safety decision issued by an authority, often using forecasts and local conditions as inputs.
