Tropical Storm Cristobal could soon renew its strength by merging with another storm system to form a large cyclone. After drenching much of the South, forecasters now expect the storm to bring fierce winds and heavy rain to much of the Midwest by Tuesday.

Forecasters say significant river flooding is possible in the upper Mississippi River valley. The storm weakened to a depression on Monday after inundating parts of the U.S. Gulf Coast.

All that water will pose challenges downstream, with smaller rivers and creeks expected to crest mid-week.