About the Tropical Cyclone Tracker

The Tropical Cyclone Tracker runs inside the WeatherMesh-6 forecast itself, tracking storms directly in the model across all 128 ensemble members.

Paths

A path is a single cyclone track from a single ensemble member. Everything else on these endpoints derives from this set of member paths. Within each member, we detect candidate centers at every forecast hour and link them across hours into a continuous track. Each point's storm_type is reported as tropical depression ( TD ), tropical storm ( TS ) or extratropical ( EX ). For non-extratropical points, the TD , and TS categories are determined from WeatherMesh-6 wind speed. Member paths are served from 0–360 h at 3-hourly spacing.

Mean path

The mean path is the ensemble mean of the member tracks, not a track of the ensemble-mean field. Averaging the pressure field first smears the vortex and yields a measurably worse track. Each forecast hour is averaged independently and requires at least 30% of the ensemble (39 of 128 members) to contribute. Below that the forecast hour is dropped rather than carried by outliers. Every vertex publishes this number as contributing_members_count .

Because a mean is tested hour by hour, a mean path can end early, contain gaps, or be empty.

Only storms with an operational ATCF ID have a mean path. An unmatched single-member track is served as its own storm with contributing_members_count: 1 and no cone.

Cone

To calculate the cone, we apply a lead-time-dependent uncertainty radius around each matched member track, out to forecast hour 168. Each member contributes a weight that decreases linearly with distance from its path. These contributions are combined and normalized by the full 128-member ensemble. The cone contains the locations where the combined, distance-weighted member support is at least 20%. No cone is returned if fewer than 26 members match, if support never reaches 20% anywhere, or if the resulting area is under 6,000 km².

Landfalls

A landfall is one water-to-land crossing by a single member's track center. It is not a property of the mean path and not a probability. The endpoint returns the raw set of crossings across all matched members. Coastlines come from NOAA GSHHG 2.3.7's high-resolution shoreline polygons, and position, time, wind, and pressure are interpolated along the crossing segment.

Crossings are grouped by connected land component and de-duplicated within 20 miles by geodesic distance, so two nearby islands yield two landfalls while a track following a coastline does not yield 50. Crossings classified as extratropical at landfall are not counted. Unlike the cone, landfalls run the full 360 h forecast.

Basin

A storm's basins list includes every basin the storm has occupied across its published forecast cycles, in the order it enters them. Most storms return a single basin; a storm that crosses a boundary, such as a Western Pacific system moving into the North Indian Ocean, returns both.

Genesis

Genesis is the ensemble's earliest tropical onset, not its average onset. We take the first hour any matched member turns tropical or subtropical, then average the position across only those members that develop at exactly that hour.

This is biased early by construction. A single fast member sets the genesis hour, and only members that agree with that hour contribute to the position so when one member leads the pack, genesis reports that member's position rather than a consensus. Treat it as the ensemble's earliest plausible onset, not its expected one.

start_time is the genesis time; end_time is the latest hour any matched member reaches.

Maximum wind and minimum MSLP

At a track point, max_wind_kt is the maximum ensemble-mean 10 m sustained wind around that point, and min_mslp_hpa is the ensemble-mean minimum central pressure of the detected storm.

The wind is a grid-cell mean from our model, and our current 0.25° cell cannot resolve an eyewall. It is not equivalent to the 1-minute sustained wind on an operational advisory and will read low for intense, compact storms.

Storm identification

Whether a track gets an operational ID determines whether it gets a mean path and a cone at all. We get currently active storms from the meteorological agencies, tracking them and use its historical path plus that forecast-guided path. Every single member track is compared to those paths and assigned to the closest storm it follows, provided it comes within the allowed matching distance. That distance increases farther into the forecast to account for growing track uncertainty.

Once a storm has its members, we name them, average them into a mean path, and draw its cone.

Some member tracks don't match active storms. These are usually systems the ensemble is developing at later forecast hours. These are kept and served under internal IDs and assigned when storms become active. Once a generated ID is matched to an operational storm, the operational ID is used in listings, but the generated ID remains a valid query alias.