A parametric reconstruction fills in the 1926 Miami hurricane's missing wind field

A parametric model does not simulate the atmosphere. It takes a short list of numbers about a storm, including intensity, the radius of maximum wind, the radii of tropical-storm-force winds and the track, and draws the surface wind swath those numbers imply, colored to the Saffir-Simpson categories ^[8]. For 1926, most of those numbers were never entered into the official record ^[7].

McNoldy started where there was something to anchor to. "Filling in the many gaps began with some estimates of the symmetric extent of the tropical-storm-force winds when environmental surface pressures were known in addition to the storm's central pressure," he said ^[9]. He worked with John Knaff, a NOAA meteorologist who specializes in tropical cyclone size estimation and whom he has known for nearly 30 years ^[11].

Eleven days at six-hour spacing is 44 intervals, or 45 time points, and each point needs a tropical-storm-force wind radius in four quadrants plus an eyewall size ^[13]. That is five numbers per step, roughly 225 in all ^[19]. McNoldy said: "The new information is a best guess of the quadrant-specific extent of tropical-storm-force winds and the eyewall size every six hours for 11 days" ^[13]. He also said: "Recognizing the uncertainties surrounding the storm size estimates, it fits our sparse observations rather well" ^[14].

Wind speeds of the kind quoted for 1926 are not the winds a city feels. "The wind speeds we hear on television and on the internet are calibrated for over the ocean, where the surface is fairly smooth compared with land surfaces. As hurricanes move over land, the wind near the ground is reduced substantially. So, I provided Brian with a formula to convert the over-ocean wind speeds to something more accurate over land," said David Nolan, a professor in the Rosenstiel School's Department of Atmospheric Sciences ^[16][15]. The formula needs a roughness value for each kind of surface: farmland, suburban homes, thick trees or tall buildings ^[17].

The 1926 storm stands alone in Miami's record. "There is nothing like the 1926 hurricane in the historical record for Miami," McNoldy said, adding that it "was very intense, very large and passed directly over downtown. It came at a time when forecasts were primitive, warnings were insufficient and people were inexperienced" ^[3][4]. The first warning for the Miami area came only a few hours before landfall ^[1].

So the benchmark storm for downtown Miami is also the one with the fewest observations behind it. The phys.org report does not say where the maps were published, what the numerical bounds on the quadrant radii are, or whether any risk or surge model has used the swath as an input ^[20]. On footprint the reconstruction is definite: McNoldy said the storm was "very large, in contrast to something like Hurricane Andrew, which was extremely small" ^[14].