How to read HawaiiStorm
What each part of the dashboard shows, and how to use it to decide what to do on your island.
Start here
Pick your island at the top of the page. Every tile then answers for that island: how close the storm comes, the strongest gust expected, and the surf, rain and surge.
Simple gives you the answer and the few things behind it. Full data shows everything: the map with all its layers, the model tracks, wind reach, every alert and the readings from each island. You can switch at any time; nothing is lost.
The storm
- Max wind is the strongest wind near the centre, averaged over one minute. Gusts run higher. At 39 mph a storm gets a name; at 74 mph it becomes a hurricane.
- Pressure is the air pressure at the centre. Lower means a stronger storm, so a falling number usually means it is strengthening.
- Motion is how fast the centre is moving. For Hawaii, speed matters more than heading. A slow storm sits over the same places and its rain piles up: Lane (2018) slowed to about 2 mph near the Big Island and dropped 52 inches of rain at Mountain View. A fast storm is often being torn at by winds aloft, but it is not harmless: Iniki (1992) sped up to about 29 mph as it crossed Kauai.
- Centre is where the middle of the storm is. Damaging winds reach well beyond it; wind reach shows how far.
These come from the National Hurricane Center and Central Pacific Hurricane Center advisories, issued every 6 hours, and every 3 hours while watches or warnings are up. "kt" is knots: 1 kt is about 1.15 mph.
The cone and the track
The cone shows where the centre of the storm will probably go. Historically the centre stays inside it about two-thirds of the time. It says nothing about the storm's size: damaging wind, heavy rain and high surf often reach far outside it. Being outside the cone does not mean you are safe.
The track is the path so far (solid) and the official forecast path (dotted), with the storm's forecast strength at each point.
Model guidance
Before forecasters draw the cone, they look at what dozens of computer models predict. The guidance layer shows those predictions on the map: one line for each model's forecast of where the centre will go.
- Thin, unlabelled lines are the members of NOAA's GEFS ensemble: the same model run many times with slightly different starting conditions. On their own they mean little; together, their spread is the message.
- Labelled lines are individual models from agencies around the world, including the Navy's NAVGEM and COAMPS-TC and hurricane models such as HWRF and HAFS. Click a label for what that model is and how far it sits from the official forecast.
- Consensus lines average several models together. They are often the most reliable single guide.
How to use them: read the spread, not any single line. A tight bundle means the models agree and the forecast is firmer; a wide fan means real uncertainty. The official track and cone already weigh all of these models (and some not shown here), so plan by the cone. Treat one model off on its own as a possibility worth watching, not the forecast.
In Full data the guidance layer starts off so the map stays readable. Press guidance above the map to show it. You can also hover a dot in the odds strip to light that one forecast on the map, or click it to see it alone next to the official track.
Your island's odds
The odds strip counts how many of the ensemble's forecasts bring the storm's centre close to your island, sorted into four bands by closest approach:
- ◆ Direct hit, within about 45 miles (75 km): the centre passes over or beside the island. Hurricane winds on land.
- ▲ Storm-force, about 45 to 125 miles (75 to 200 km): inside the storm-force wind field. Trees down, outages, dangerous driving.
- ● Fringe, about 125 to 250 miles (200 to 400 km): outer rain bands and gusts, high surf. Unpleasant, rarely destructive.
- ○ Clear, beyond that: outside the wind field. Maybe swell on exposed shores.
Each dot is one forecast; the blue tick is the official NHC track. If most dots sit in one band, the forecast is firm. If they scatter across bands, prepare for the worse of the likely outcomes, not the average.
Wind reach
How far from the centre damaging winds reach right now, in each direction (quadrant): tropical-storm-force (39 mph and up), 58 mph and up, and hurricane-force (74 mph and up). Storms are rarely round. In the Northern Hemisphere the strongest winds are usually on the right side of the direction the storm is moving, so the same storm can be much worse on one side of an island chain than the other.
On the map, radii draws these areas, and swath shows where tropical-storm and hurricane-force winds have already been.
Other map layers
- outlook: areas forecasters are watching that could become storms, with their odds for the next 2 and 7 days.
- alerts: warning areas on land, and coastline under a hurricane or tropical storm watch or warning.
- radar: rain and thunderstorms right now, from National Weather Service radar.
- wind: surface wind, animated from a weather model: where the air is flowing and how fast.
- fit storm: zooms out to show the storm's whole track and cone.
On a computer, point at any button above the map for a one-line description. On a phone, What are these? lists them all.
Alerts
Every active National Weather Service alert for Hawaii. The Weather Service issues the same warning once per forecast zone, so dozens of raw alerts are grouped into the few real ones ("Hurricane Warning · 8 areas"), with the areas that cover your island marked.
A watch means the conditions are possible, usually within 48 hours. A warning means they are expected, usually within 36 hours. A warning is the signal to finish preparing.
Conditions, surf and tides
- Islands now: temperature, wind, gusts and pressure on each island, with storm-force gusts marked.
- Six agencies: the gust forecast from six national weather agencies (Europe, the United States, Germany, Japan, the United Kingdom and France) at the island the storm comes closest to; the tile's title names the place and time. Where they disagree is the uncertainty.
- Sea and tides: wave height and swell, and the water level at the nearest NOAA tide gauge. Surge is how far the water is running above the predicted tide; a storm pushing water ashore shows up here first. Molokai, Lanai and Maui share one gauge (Kahului Harbor).
- Buoys, on the map: live wind, waves and pressure from ocean buoys around the islands. A falling pressure at a buoy between you and the storm is an early sign it is closing in.
The timeline
Press play or drag the handle to move through the storm's life, from where it has been to where it is forecast to go over the next five days. The map and the readouts follow. The tick labelled with your island's name marks the storm's closest approach to it. Press now to return to the present.
Is the data current?
The status at the top says live when every source is answering, and partial when one is not; open it to see how old each source's data really is. Every source is refreshed every few minutes.
To save your data, HawaiiStorm slows down when you switch to another tab or leave the page alone for 10 minutes: it then updates every 5 minutes, and the status pulses and says how old the data is. Press Refresh there to go back to live updates.
Official sources
HawaiiStorm is not an official source. For life-safety decisions follow the National Weather Service in Honolulu (opens in a new tab), the Central Pacific Hurricane Center (opens in a new tab) and your county emergency management agency (Hawaii Emergency Management Agency (opens in a new tab)).
HawaiiStorm covers the Hawaiian Islands only. If you are outside Hawaii, follow your local weather service.