Hurricane Ike Rainfall

Paul Lewis
NWS Houston/Galveston
Updated - November 25, 2008

NOTE: This is a preliminary discussion based on available rainfall data. This discussion will be updated as other data sources become available.

Hurricane Ike produced heavy rainfall across portions of southeastern Texas September 12-13, 2008. A cold front then moved across these same locations on the 14th and heavy rainfall developed as moisture feeding into the remnants of Ike was focused along the front. Rainfall totals on the 14th equaled or exceeded those associated with Ike and some locations experienced flooding during both events.

The National Hurricane Center estimated that Ike moved northwest between 12 and 18 mph across southeastern Texas. The general rainfall estimate rule-of-thumb for a landfalling tropical cyclone is to divide the speed of the storm's movement into 100. When utilizing an average speed of 15 mph for Ike, this calculation gives an estimate of close to 7 inches. Actual rainfall recorded for Ike was between 5 and 10 inches across the 9 county area that ranges roughly between Livingston and Navasota south to the coast. Rainfall ahead of the cold front totaled another 5 to 8 inches. By the evening of the 14th, rainfall maximums of near 15 inches had fallen across portions of Houston, Liberty, and Montgomery Counties. In the uptown area of Houston, isolated observations of around 18 inches were recorded.

Moderate to heavy rainfall began as Ike's rain bands moved into the upper Texas coastal areas during the afternoon and evening of the 12th. These rain bands intensified as Ike made landfall at Galveston around 2:10 AM CDT of the 13th. The radar data then showed that the heaviest rain fell on the northern and western sides of the eye of the storm as it moved northwest up Galveston Bay and into the eastern portions of metropolitan Houston during the pre-dawn hours. The heaviest rainfall area then shifted to over the southern half of Ike as the storm moved north of Houston. Because of this, portions of Harris, Montgomery, and Liberty Counties experienced moderate to heavy rainfall for about a 12-hour period.

Figures 1 and 2 give the rainfall amounts measured by the Harris County Flood Control District for the 24-hour periods ending at 6:00 PM CDT on September 13 and September 14 respectively. Figure 3 presents the total rainfall for the 2-day period.

Figure 1 - September 12-13, 2008 24-Hour Rainfall for Harris County

Figure 2 - September 13-14, 2008 24-Hour Rainfall for Harris County

Figure 3 - September 12-14, 2008 48-Hour Rainfall for Harris County

The West Gulf River Forecast Center (WGRFC) in Fort Worth made corrections to the KHGZ radar precipitation due to the radar bias and that recorded by rainfall gages. These graphics with the gage data incorporated are shown in figures 4 - 7. Figure 4 presents the rainfall associated with landfall of Ike through 7:00 AM CDT September 13, 2008. Rainfall that fell during the next 24-hour period ahead of the cold front is shown in Figure 5 while residual rainfall behind the cold front is given in Figure 6. The total rainfall for the 3-day period is presented in figure 7.

Figure 4 - Hurricane Ike 24-hour RFC Corrected Rainfall Ending 7:00 AM CDT September 13, 2008

Figure 5 - Prefrontal 24-hour RFC Corrected Rainfall Ending 7:00 AM CDT September 14, 2008

Figure 6 - Post Frontal 24-hour RFC Corrected Rainfall Ending 7:00 AM CDT September 15, 2008

Figure 7 - Hurricane Ike RFC Corrected Rainfall 3-Day Total Ending 7:00 AM CDT September 15, 2008

Thanks to the West Gulf River Forecast Center for their help in providing rainfall graphics and to Dave Schwertz, the WFO Houston Service Hydrologist, for his expertise and help with the graphics.