On the Nuances Associated with Analyzing Historical Rainfall Observations before and during the Great New England Hurricane of 1938

On September 21, 1938, the Great New England Hurricane of 1938 raced through Long Island and New England, leaving behind several hundred casualties and enormous devastation from the coast to the forest. Besides the coastal flooding due to the large storm surge accompanying the storm, there was also widespread, and in some places record-breaking, river flooding. The rainfall accompanying the hurricane was significant, but not extraordinary. A preceding rainfall event, however, had brought great amounts of precipitation that had saturated the terrain, severely limiting the capacity of the ground to absorb the additional rainfall brought by the storm. These water surplus flooded bodies of water and made the soil so soft that countless trees were easily blown down by the hurricane winds.

The purpose of this study is to carefully reevaluate the amounts of precipitation measured throughout the region and recorded in NCDC daily data to determine how much rain fell before and during the Hurricane. In order to do this properly, one must take into account all the nuances resulting from the different timing of the various measurements (some in the morning, some in the afternoon and some midnight-to-midnight). It is also desirable to clearly separate the precipitation from the preceding rain (most likely a predecessor rainfall event or PRE, as recently defined) and the hurricane. The common practice to add the total hurricane rainfall has been to average the September 19 to 22 daily rainfall, but this would include part of the PRE rainfall, therefore artificially increasing totals during the hurricane. In the process, new locations emerge as the ones with the highest rainfall totals.

The author will discuss the difficulties in dealing with the historical precipitation data, present the revised rainfall statistics and maps related to this particular storm and highlight other hydrological measurements available. This study is part of a larger project, a book on the meteorology and history of the Great New England Hurricane of 1938, which will soon be published by the American Meteorological Society.