Tropical Storm Isaac will ease but not end drought

(CBS News) Tropical Storm Isaac is currently on track to barrel over New Orleans and right up the Mississippi River, dumping up to 10 inches of rain on parts of the U.S.

With a record drought choking a majority of U.S. counties, especially in the Midwest, Isaac will bring some much-needed relief. For the worst-hit parts of the country however, a torrent of rain accompanied by driving winds could make things worse.

"A lot of that rain comes so fast and furious that it's not effective. It doesn't work its way into the groundwater, helping with soil moisture," said Mark Svoboda, a climatologist at the University of Nebraska at Lincoln's National Drought Mitigation Center, in a telephone interview with CBS News. "It depends where and how fast and how furious."

Some of the worst hit parts of the country for the drought - the central plains around Nebraska and Arkansas - are going to be too far west to benefit from Isaac's rains, Svoboda said. However, places like Georgia and Alabama, as well as Illinois and Missouri further upriver, will get a lot of help on Isaac's current path.

"It could improve their situation. That's a two-year drought (in the Georgia and Alabama region.) A lot of that is due to the quiet tropical storm season the last two years now," Svoboda said.

When heavy storms unleash lots of water in a short period of time on parched land, much of it ends up as runoff because the soil can't absorb it in time. Additionally, the rain from Isaac will come too late for crops like corn and soybeans, but just in time to help with late season wheat and hay crops, as well as to help with getting the grass on parts of the plains moist enough to build up strength for the coming winter.

Kansas farmer Tyler Alpers told Reuters: "It's too late for fall crops and pasture but it will really help with fall planting of wheat in about a month."

Experts and farmers are quick to point out that the potential ten inches of rain Isaac is expected to drop along its path will not make up for the ten-inch rain deficit much of the country is experiencing.

"It will be helpful for those areas that have been in drought just this year because the drought has not been as long-lived there," said Svoboda, adding that it would take several Isaacs to fully ease the effects of the nationwide drought. Still, "Certainly this is what we need to replenish ground water."