430
AGUS74 KWCO 211158
HMDNWC

National Hydrologic Discussion - EXPERIMENTAL
NWS National Water Center - Tuscaloosa AL
700 AM CDT FRI AUG 21 2026

.Update...

The northern edge of the limited risk area was trimmed to account for
changes in the QPF. Additionally, talking points were adjusted to account
for potential for urban flooding today and Saturday within the
aforementioned area. No other significant changes to the Flood Hazard
Outlook.

//RKursky / GKendrick

Previous Discussion as Follows:

...Flash and urban flooding is possible across the Mid-Atlantic into the
Northeast through tonight and the Carolinas into Virginia tomorrow evening
and afternoon... Isolated moderate and major river flooding is ongoing or
forecast in the Ohio Valley... For Guam and the Northern Mariana Islands,
flash flooding impacts remain possible this weekend into early next week
due to Tropical Storm Saudel and mudslides are possible in areas of steep
terrain... Flooding impacts are becoming increasingly likely on the Big
Island of Hawaii this weekend...

.Mid-Atlantic into the Northeast...
The system that swept across the Ohio Valley last night has made its way
into Pennsylvania, and associated rainfall will continue to work its way
southward along the coast through tonight. Much of central and eastern
Pennsylvania and and the coastal Mid-Atlantic could see flash and urban
flooding impact, and with rainfall totals of 2 - 3" (locally higher), there
is a locally considerable threat for flash and urban flooding along the
Northeast Corridor. Antecedent conditions are not especially primed, but
the heavy urbanization and potential for high rainfall rates leaves the
area vulnerable to flooding impacts. Recent runs of the HRRR-forced
National Water Model (NWM) have been signaling potential for significant
flows across northern New Jersey into Connecticut, with annual exceedance
probabilities (AEPs) in the 20 - 4% range. Rapid-onset flooding (ROF)
probabilities have been ticking upwards with subsequent runs, and that same
area is now in the 25 - 75% range. Timing-wise, most low-order streams
should have peaked by midnight. Signals elsewhere throughout the region are
more muted, but with isolated reaches exceeding the 50% AEP threshold,
flooding impacts cannot be ruled out.

.Carolinas into Virginia...
Flash and urban flooding are possible Friday afternoon and evening. Soils
are very dry and streamflows are well below normal. This combined with the
sandy soils will help to mitigate any widespread impacts however, isolated
instances of flash and urban flooding cannot be ruled out. This is also
reflected in the NWM Medium Range Forecast signals which are currently very
isolated. The NWM Short Range Forecast may provide a clearer picture of
flooding impacts  given its higher resolution once it captures the forecast
QPF tomorrow morning. Nevertheless, this area will have to be monitored
today and tomorrow.

.Ohio Valley...
Moderate river flooding is ongoing along the White and Wabash Rivers in
Indiana and moderate to major river flooding is forecast on the South Fork
Licking and Licking Rivers in Ohio.

.Guam and Northern Mariana Islands...
Flash flooding impacts remain possible this weekend and into next week due
to the northward passage of Tropical Storm Saudel. Mudslides also are
possible in areas of steep terrain.

.Hawaii...
Heavy rainfall from Tropical Depression Two-C is expected to begin over the
Big Island late Saturday. Uncertainty in the magnitude of the rainfall
remains high, but with the area already sensitive due to the recent
flooding from Hurricane Lala, any additional rainfall could lead to
additional flooding and impacts to travel, some of which could be
significant.

//Bliss

Additional National Water Center products are available at
www.weather.gov/owp/operations


$$