2 tropical storms bring flooding, drought relief

How quickly things can change. In just 3 weeks, North Carolina was impacted by Tropical Storm Hanna and the remnants of Tropical Storm Fay.

Fay brought rainfall to central and western North Carolina in late August, including nearly 12 inches to parts of Mecklenburg and Cabarrus Counties. This rain brought substantial flooding to these areas, but also provided needed drought relief. Just goes to show - you don't need a Category 3 hurricane to bring damaging floods.

Map of estimated rainfall between August 25, 2008 and August 31, 2008 – the period when the remnants of Tropical Storm Fay impacted North Carolina.

Tropical Storm Hanna made landfall near the NC-SC border during the evening of Sept 5, and brought 3-7 inches to central and southeastern NC. Flooding from Hanna was much more limited, but also provided the second punch to drought conditions in central NC.

Map of estimated rainfall between September 6, 2008 and September 9, 2008 – the period when Tropical Storm Hanna impacted North Carolina.

Much of central NC, including parts the Triangle area, have received more than 10 inches of rainfall in less than 20 days. This equates to approximately a 5-year event based on precipitation frequency statistic from the National Weather Service.

And a big shout out to all those dedicated Coop and CoCoRaHS observers - the rainfall reports from all the volunteer observers makes analysis of these storms SOOOOO much easier and accurate. The map above shows CoCoRaHS observations from September 6, 2008.

So there's no drought anymore in NC, right? Well...

Conditions in central NC are certainly much improved, and one is hard pressed to find any drought impacts in this region. However, you don't have to go too far west or too far east to find impacts. Indeed, D3 conditions are still widespread in the far western counties, and the counties north of the Albemarle Sound are still showing severe (D2) drought impacts. But most of central NC is D0 or D-nothing - so no drought impacts.

What?!! You mean we've had 2 tropical storms, lots of flooding, and there's still drought? Yup - here's why. Drought emerges slowly, over many weeks to months. Rain from tropical storms falls in days. The ground just can't absorb it all that fast. What doesn't get absorbed goes to runoff. Runoff is great if you have a surface reservoir to capture it, but 7 inches of rainfall doesn't provide as much benefit for groundwater. And groundwater provides the base flow for streams and water supplies for many smaller communities. Indeed, groundwater levels in western NC and northeastern parts of the state are still very low for this time of year. 7 inches of rain spread out evening over 2 weeks would provide much more drought relief than 7 inches in 2 days.

State Climate Office moves to new location

For all you readers out there who have followed the climate office activities over the past decade or so remember the great move of 2001, the squeeze move of 2003, and the expansion move of 2007. Well, we're at it again. We've moved everyone down to the first floor of the Research III Building on the Centennial Campus of NC State University. Same building and little less space, but hey - we got new paint and carpet in the process. Our phone numbers, website, and e-mail addresses remain unchanged.