Case Review: September Heavy Rainfall from Landfalling Hurricane Summary of Hurricane Floyd Rainfall Excessive rainfall associated with Hurricane Floyd occurred on September along the eastern seaboard from coastal South Carolina to New England. Some of the greatest 24-h amounts occurred in the eastern Carolinas on 15 September, and from the Chesapeake Bay northward to western New England on 16 September. Large areas greater than 6 inches in 24 hours occurred, with local amounts exceeding 12 inches in the eastern Carolinas, and over 9 inches in northern New Jersey and the lower Hudson Valley of New York. Matt Kelsch COMET RFC/HPC Hydromet 02-1

Case Review: September Heavy Rainfall from Landfalling Hurricane Summary of Hurricane Floyd Flooding & Impact More than 60 people lost their lives primarily from inland flooding, and mainly in the Carolinas. Historic flooding of main stem rivers occurred in much of eastern North Carolina, with some notable flooding all the way up into New England. However, the region had been in a severe drought, and many watersheds and stream channels in the Northeast were able to handle the excessive rainfall and runoff. Matt Kelsch COMET RFC/HPC Hydromet 02-1

Tar River near Tarboro

HPC Day 1 Verification valid 1200 UTC 17 Sep 99

Case Review: September Heavy Rainfall from Landfalling Hurricane Summary of Hurricane Floyd Rainfall Production Floyd was an example of a hurricane interacting with a mid-latitude baroclinic system to produce excessive rainfall north and west of its track. The primary precipitation processes: Abundant maritime tropical moisture in the low levels, Frontogenesis enhancing the lift in the low levels, which is where rainfall production is concentrated in maritime tropical air masses, Significant isentropic lift of moisture laden air in the low levels, Topography likely played some role in the localized heavy rain in the Northeast, but the meteorological processes would have produced widespread heavy rain anyway. Meteorological processes associated with frontogenesis were most important as seen in the following images.

ETA 1200 UTC 16Sep99 analysis: 300-K sfc Wind and Pressure, with PW image.

ETA 6-h Fcst valid 1800 UTC 16Sep99: 925 mb Wind, Omega, and Frontogenesis Image

Frontal positions at various times, 24-h accumulation (>5” dashed red, ~7” dashed orange).

Case Review: September Heavy Rainfall from Landfalling Hurricane Summary of Hurricane Floyd Rainfall, cont. The low-level precipitation production was typical of maritime tropical air masses. Storm cells were generally low-centroid compared to typical thunderstorms in the mid-latitudes. Thus, the radars were under sampling the precipitation particles at distant ranges, resulting in underestimation of rainfall in those areas. Further inland in the polar air mass, the freezing level was lower causing a prominent bright band in the radar-derived precipitation (KENX).

Albany NY WSR-88D Storm Total Accum.

Case Review: September Heavy Rainfall from Landfalling Hurricane Summary of Hurricane Floyd disaster Despite the media attention to the dangers of storm surge and high wind, Floyd had a much more severe impact from the inland floods. Recent hurricane and tropical storm disasters have demonstrated the serious dangers of inland flooding, sometimes long after the threat of coastal damage is over. This is true even for major hurricanes like Floyd. –Camille 1969 –Agnes 1972 –Alberto 1994 –Fran 1996 –Mitch 1998