The flood threat will continue for yet another day along the East Coast as a persistent firehose of tropical moisture from the Gulf of Mexico provides a conducive environment for heavy rain, possibly leading to flash flooding because of the already saturated soil.
The Weather Prediction Center has placed western Maine through the coastal Carolinas down to the northern Georgia coast on a Slight Risk for excessive rainfall through tonight. This indicates a 10 to 20 percent chance for the occurrence of flash flooding within 25 miles of a location.
This outlook correlates very well with where the highest predictable water will be located. Most areas can expect values at some point this Friday to exceed 2 inches, indicating a highly moist atmosphere. In New England this high moisture content is somewhat unusual, and as a consequence it will likely feel like the tropics as the moisture hangs around.
This morning, there is a line of light showers extending from northern New England through central portions of New York and Pennsylvania. As the day progresses, lines of rain and thunderstorms are expected to develop across these same areas while numerous hit or miss storms form ahead of it, threatening much of the I-95 corridor. The only part of the Northeast that can expect a dry day is southeastern New England due to the close proximity of the strong, 1025 millibar Bermuda High.
Now while some storms in the Northeast may bring flooding, the risk is more concerning in the Southeast, especially this morning in and east of the Appalachian Mountains in North Carolina, Virginia, and West Virginia. Some locations have already received over half a foot of rainfall this week, so the ground is beginning to become too saturated to handle any more rain. Flash flooding can be expected in numerous locales as a result.
Across the remainder of the Southeast this morning, there will continue to be widely scattered showers and storms. Then in the afternoon, the daytime heating will allow for these storms to blossom, becoming more widespread. Some locations, especially in the Carolinas and Virginia, may deal with several consecutive hours of heavy rain.
Tonight, much of the shower and thunderstorm activity is expected to diminish in the Southeast, while rounds of potentially heavy rain and thunderstorms push through much of the Mid-Atlantic and New England.
There may also be a severe component with these storms, both today and tonight, especially from central New England through central Virginia. Damaging winds will be the main risk, but a spin-up tornado or two cannot be ruled out due to the strong low-level winds.
Rainfall will vary given the nature of these storms. While some towns receive possibly no rainfall, other towns will likely pick up over 3 or 4 inches through tonight.