


Hydrometeorological Discussion
Issued by NWS Tuscaloosa, AL
Issued by NWS Tuscaloosa, AL
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 $$