Hurricane Harvey the Name Says It All

Hurricane Harvey came ashore near Rockport, Texas around 0300 UTC 26 August 2017 as a category 4 storm. Winds in Rockport reached 130 mph. Most of the wind damage was focused close to the storm center. As the storm moved inland and then re-entered the Gulf of Mexico the extreme rainfall associated with the storm system became the most critical issue.

The rainfall associated with Harvey exceeded 1000 mm (50 inches) with a large swath of eastern Texas receiving over 300 mm of rainfall. The extremely heavy rainfall resulted in record flooding over most of northeastern Texas and the Houston metropolitan area. The damage to infrastructure and flooded automobiles will likely make Harvey one of, if not the most costly weather disasters in United States.

This paper will document the rainfall associated with Harvey and show forecasts of the rainfall. It will be shown that the NCEP GEFS produced extreme rainfall amounts. Operational GEFS forecasts of QPF verse the internal model QPF climatology (M-Climate) showed that the GEFS consistently forecast record rainfall within the modelling system for several days prior to the flooding and at nearly all 6,12,24,36, 48, and 72 hour forecasts lengths. This historic rainfall event demonstrates the need for model climatology to gage both the meteorological and climatological significance of an event.

Despite the success of these forecasts, there was considerable uncertainty as to where the heaviest rain would fall. Predictability diagrams are used to show how well the GEFS forecast the event but also how some of the details were harder to predict.

A brief summary of high resolution ensemble data is used to show how valuable these data are in refining the threat for extreme rainfall and show where extreme rainfall is most likely to occur. For DSS activities, these high resolution tools show great potential to improve short range DSS activates.