Using Precipitable Water and Showalter Index Sounding Climatologies to Better Predict Heavy Rainfall Events in American Samoa and Developing a Flash Flood Threshold Based on Observed Gauge and Sounding Data

Scientific flash flooding research hasn’t been performed on the island of American Samoa
since the mid-1960s. The National Centers for Environmental Information (NCEI) and the
University of Wyoming’s Meteorological Department provides historical observational
sounding data for the entire world. These databases are used in research and to support
operational forecasting. A climatology of precipitable water (PWAT) and Showalter index (SI)
was completed for the Weather Service Office in Pago Pago, American Samoa, which was
important for this research project as a sounding climatology had not been available to the
forecasters in Pago Pago. Additionally, rain gauge data was compared to the NWS storm
events database to assess where the current thresholds were.

A discussion of the methods and programming used and the forecasting applications will be
presented. In addition, a potential rainfall index will be developed from previous literature and
findings from this research to assist in operational forecasting and issuance of flood products
to better protect life and property. Additional uses and data will be discussed further with
examples of applications to operational forecasting and verification of the research