Tropical Storm Arthur is forecast to inch slowly north northeastward over the southern Mid-Atlantic on Thursday. This system will be situated just to the east of Georgia and South Carolina, and is expected to bring showers and thunderstorms to northeast Florida, eastern Georgia and the Carolinas. Arthur will likely be upgraded to a category 1 hurricane, with wind speeds ranging between 74 to 95 mph (64 to 82 kts).
Meanwhile, a cold frontal boundary will stretch across the southern Plains, the lower Mississippi Valley, the Appalachians and the Northeast. As this system overruns a warm, humid air mass, rain and thunderstorms will develop across New England, the northern Mid-Atlantic, the eastern Ohio Valley, Gulf Coast and the southern Plains. Thunderstorms along the East Coast will interact with Tropical Storm Arthur, which could lead to flash flooding over eastern Virginia, eastern Maryland, Delaware and southern New Jersey. A ridge of high pressure will build behind this frontal boundary, keeping conditions cool and dry across the western Ohio Valley and the upper Midwest.
A separate frontal boundary will extend across the Intermountain West on Thursday. Scattered showers and thunderstorms will develop across the Rockies and the Four Corners as a result of this system. An area of low pressure will also move across the Northwest, ushering rainy weather over parts of Washington. A ridge of high pressure will keep conditions clear across the Southwest.