HURDAT2 is the National Hurricane Center's "best track" database: for each tropical and subtropical cyclone, the Center's final assessment of where it was, how strong it was and what kind of system it was, made after the season with every observation available, including ones that did not reach forecasters in real time. It comes as two plain-text files, one for the Atlantic since 1851 and one for the north-east and central Pacific since 1949, and the Center publishes a description of the format.
Every storm page and city page on this site is built from those two files. For the 737 storms that passed within 75 miles of a US city, the database here holds 23,963 positions.
What a record contains
Each storm starts with a header line: an identifier made of the basin, the storm's number in the season and the year (AL092011 is the ninth Atlantic system of 2011), its name or UNNAMED, and the number of lines that follow. Each following line is one moment in the storm's life: the date and the time in UTC; a one-letter record identifier that marks special points such as L for a landfall, where the centre crossed a coastline, or I for an intensity peak; the status code; the latitude and longitude of the centre; the maximum sustained wind in knots; the minimum central pressure in millibars; and, for recent storms, the radii of 34-, 50- and 64-knot winds in each quadrant.
Positions are given every six hours, at 00, 06, 12 and 18 UTC, with extra lines at landfalls and intensity peaks. Of the positions held here, 861 (3.6%) fall between the six-hour times. This site keeps the time, position, wind and status of every line, and measures each city's distance to the straight segment between consecutive positions, not just to the positions themselves.
Status codes
The status code says what kind of system the storm was at that moment. A storm can change status many times: it may start as a disturbance or a tropical depression, become a hurricane, and end as an extratropical low over the North Atlantic. Only tropical-storm strength and above counts for a city on this site, whatever the status.
| Code | Meaning | Positions near-US storms |
|---|---|---|
| TD | Tropical cyclone of tropical depression intensity (under 34 knots) | 3,484 |
| TS | Tropical cyclone of tropical storm intensity (34–63 knots) | 9,351 |
| HU | Tropical cyclone of hurricane intensity (64 knots or more) | 7,444 |
| EX | Extratropical cyclone, of any intensity | 2,752 |
| SD | Subtropical cyclone of subtropical depression intensity (under 34 knots) | 113 |
| SS | Subtropical cyclone of subtropical storm intensity (34 knots or more) | 193 |
| LO | A low that is neither tropical, subtropical nor extratropical | 425 |
| WV | Tropical wave, of any intensity | 72 |
| DB | Disturbance, of any intensity | 129 |
Meanings from the National Hurricane Center's format description.
One track, line by line: Ivan 2004
Ivan 2004 has 94 lines in HURDAT2, covering 22 days from its first position as a TD to its last. Its peak was 167 mph (145 knots), a Category 5 storm, on 2004-09-11 18:00 UTC at 18.0°N 79.0°W. The table shows the first and last lines, the peak, and every line where its status changed. Its closest pass to a city on this site was directly over Pine Hill, AL, at 68 mph on the track.
| Time | Status | Position | Wind (kt) | Wind (mph) |
|---|---|---|---|---|
| 2004-09-02 18:00 UTC | TD | 9.7°N 27.6°W | 25 | 29 mph |
| 2004-09-03 06:00 UTC | TS | 9.7°N 30.3°W | 35 | 40 mph |
| 2004-09-05 06:00 UTC | HU | 9.5°N 43.4°W | 65 | 75 mph |
| 2004-09-11 18:00 UTC | HU | 18.0°N 79.0°W | 145 | 167 mph |
| 2004-09-16 18:00 UTC | TS | 32.5°N 87.4°W | 50 | 58 mph |
| 2004-09-17 00:00 UTC | TD | 33.8°N 86.5°W | 30 | 35 mph |
| 2004-09-18 18:00 UTC | EX | 38.0°N 75.5°W | 25 | 29 mph |
| 2004-09-21 18:00 UTC | LO | 25.2°N 82.8°W | 25 | 29 mph |
| 2004-09-22 18:00 UTC | TD | 26.5°N 88.6°W | 30 | 35 mph |
| 2004-09-23 00:00 UTC | TS | 27.1°N 89.5°W | 35 | 40 mph |
| 2004-09-24 00:00 UTC | TD | 29.6°N 93.2°W | 30 | 35 mph |
| 2004-09-24 06:00 UTC | TD | 30.1°N 94.2°W | 25 | 29 mph |
A record that keeps changing
HURDAT2 is revised through the Hurricane Center's reanalysis of past seasons and its Best Track Change Committee, so a storm's track or strength can differ between file revisions, and storms can be added, merged or renumbered. The files are dated in their names; this site names the revisions it uses on its methodology page, along with the changes that have moved figures here.
The wind in HURDAT2 is the maximum sustained wind of the whole storm at that time, not the wind at any particular place, and the position is the centre. Both are estimates, and for storms before aircraft reconnaissance and satellites they rest on scattered ship and land reports.