Historical Hurricanes

A total of 143 hurricanes over the period 1508-1997 were investigated, including all hurricanes since 1851 that passed within 500 km of Puerto Rico according to HURDAT and all earlier hurricanes that impacted the island according to Salivia (1950), Millas (1968), and other scholars. Of these, a total of 85 hurricanes for which we found historical evidence of wind damage (F0+) in Puerto Rico were selected for detailed analysis. A wide range of Puerto Rican newspapers have provided direct accounts of hurricane impacts since 1876, and Salivia (1950) provided valuable secondary information. Evidence for earlier hurricanes was drawn from secondary studies by Salivia (1950), Millas (1968), and other scholars. Wherever possible these works were supplemented by primary sources (letters and other documents) from the University of Puerto Rico and the General Archives of Puerto Rico in San Juan.

Our analysis of temporal variation in Puerto Rican hurricanes was based on 73 hurricanes whose dates are known and whose maximum reported wind damage in Puerto Rico equaled or exceeded F1. At a seasonal scale, 84% of these hurricanes occurred during the months of August and September. At an annual scale, there were 7 years with two hurricanes in the same year, though none of these caused F3 damage. At a decadal scale, the number of hurricanes since 1851 varied from a minimum of 0 storms in the 1850s to a maximum of 7 storms in the 1890s, and evidence suggests that such multidecadal variation was present over the entire historical period (figure 2.2b). At a centennial scale, the number of F3 hurricanes was fairly constant during the historical period, with the greatest number in the nineteenth and twentieth centuries and the smallest number in the eighteenth century. At lower levels of damage, the number of F2 hurricanes increased steadily over time and the number of F1 hurricanes increased steadily until the nineteenth century. These trends are probably the result of improvements in meteorological observations and records over time.

Our analysis of spatial variation in hurricane impacts was based on meteorological reconstructions of storms since 1851 with the HURRECON model. The frequency of F0 events was probably underestimated, since F0 damage could result from storms not covered in this study. At a regional scale, the frequency of higher levels of wind damage decreased from east to west across the island, though the entire region was occasionally subject to F3 damage (figure 2.3b). These gradients result from the consistent direction of the storm tracks and the tendency for hurricanes to weaken as they pass over the island. At a site scale, estimated mean return intervals for F0+, F1+, F2+, and F3 damage in the LUQ were 4 years, 5 years, 20 years, and 50 years, respectively (figure 2.4b), with the highest winds from the northeast. At the landscape scale, the steep mountain topography produced striking differences in predicted impacts on the north and south slopes of the Luquillo mountains, with greatly reduced impacts on the south slopes.

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