El Niño Map

The live storms are Here’s: a storm is listed when its official forecast comes within 1,500 km of this point, or, with no forecast this run, it is that close now, or the point is in its peak storm surge area or within 300 km of a coast under its watch or warning. When its wind reaches here is worked out from the official forecast hour by hour, centre, wind and wind radii interpolated linearly between forecast times, as the exposure table does, so a radius the forecast does not give is not forecast, never zero; this is not an official product. Distances are great-circle; every time is UTC.

The replay plays a live storm’s official forecast hour by hour as Here reads it, or a past storm’s best track from HURDAT2 since 2004, the first season it gives wind radii, made hourly by the same rules: the centre and its wind interpolated linearly between fixes, a radius known where the file gives one, zero where the wind is under its threshold and unknown otherwise, interpolated only between two known ends. A past storm is replayed over the hours its centre is within 1,000 km of here or its 34-kt wind is over here, six hours either side. Each hour the point’s band is the strongest wind it is inside, the next said not forecast (not known, for a past storm) where no radius gives it. A wind radius is the furthest that wind reaches anywhere in its quadrant, so the band here is the most the forecast or the analysis allows; the wind at the point may be lower.

Where the wind comes from is worked out here, not forecast: it blows round the centre, anticlockwise north of the equator and clockwise south of it, and 20 degrees in towards it, a typical inflow angle near the surface over the sea; over land the angle is larger, so the wind there blows more nearly towards the centre than shown; within 10 km of the centre it is not given. The streaks over the panorama illustrate the band; they are not a rain forecast, and they do not turn when Google’s view is turned, which the page cannot see.