813
AGUS74 KWCO 171519
HMDNWC

National Hydrologic Discussion - EXPERIMENTAL
NWS National Water Center - Tuscaloosa AL
1015 AM CDT FRI OCT 17 2025

.Synopsis...
Heavy rainfall may cause flash flooding and landslides this weekend across
American Samoa...Flash, urban, and small stream flooding is possible
through this afternoon across portions of Hawaii...Periods of isolated
flooding are possible this weekend for the Lower Mississippi into the Great
Lakes...A series of atmospheric rivers are forecast in the Pacific
Northwest and may elicit hydrologic responses late next week...Afternoon
showers may elicit flooding through early next week in Puerto Rico...

.American Samoa...
An active trough is forecast to bring heavy rainfall to all the islands
through the weekend which may cause instances of flash flooding and
landslides.

.Hawaii...
Heavy rainfall across the Kauai and Niihau islands may cause flash, urban,
and small stream flooding through this afternoon. Typical flood prone and
low-lying areas may experience closures due to rapid runoff.

.Lower Mississippi into the Great Lakes...
Showers and severe thunderstorms are forecast across the region this
weekend which may bring the threat for isolated flash flooding. These area
soils remain dry and as such much of this rainfall is likely to be
beneficial. However, pockets of intense or training rainfall can overwhelm
dry soils, and therefore, lead to enhanced overland flow and flash flooding
potential. Regardless, the concern for widespread flooding concerns remains
low due to the progressive nature of the system. Furthermore, river
ensembles and the National Water Model have yet to pick up on any discreet
river threats as the aforementioned dry summer has created an environment
with ample in-channel storage.

.Pacific Northwest...
A series of atmospheric rivers is forecast late in the period which may
bring isolated urban and small stream flooding through late next week.
While there are a few pulses expected to occur over the coming few days,
the overlapping effect of rainfall will serve to prime soils and enhance
basin vulnerability to additional input. The highest forecast QPF is
expected to begin by Fri (day 7) with a full 7-day rainfall total forecast
of 7 - 10" in basins that include the Olympic and Cascade Mountains in
Washington. While the extended range typically is associated with reduced
confidence in the forecast much of the model guidance has been showing
consistency in some appreciable rainfall possible along with ensemble river
guidance beginning to pick up increasing chances of potential river
flooding. Furthermore, as these rounds of heavy rainfall begin they may
cause urban and nuisance flooding due to leaves beginning to fill culverts
and drainage areas. While it is still too early for exact magnitude and
placement of impacts many signs point to some level of hydrologic
responses, and as such this area will need to be monitored closely as this
event continues to evolve.

.Puerto Rico...
Afternoon showers and thunderstorms will continue across the island through
the weekend into early next week which may bring an elevated risk of
flooding. While there is a low chance of flash flooding, some isolated
areas of urban and small stream flooding are possible.

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

This product will begin to be issued twice daily, with new issuance times,
beginning approximately 3 November 2025. The routine primary issuance time
of the product will be at 20 UTC, with routine daily updates to the
discussion being completed around 7 AM Central Time.

//JAC



$$