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AGUS74 KWCO 181452

HMDNWC



National Hydrologic Discussion - EXPERIMENTAL

NWS National Water Center - Tuscaloosa AL

0952 AM CDT SAT MAY 18 2024



.Synopsis...

Widespread river flooding impacts continue across East Texas and Southwest  

Louisiana... Considerable flooding impacts remain possible for portions of  

Hawaii this weekend... Locally considerable flooding impacts possible today  

across portions of the Southeast... Multiple days of rain introducing a  

localized flooding threat for the Central Plains into the Upper Midwest...  

A rainy week ahead for Puerto Rico and USVI will reintroduce the potential  

for flooding impacts across the wet islands...



.Discussion...



.East Texas and Southwest Louisiana...

Moderate-to-major river flooding is ongoing in response to all of the  

recent heavy rainfall, with many rivers still rising. Crests are expected  

to begin this weekend into next week, with flooding impacts lingering well  

into next week. There is potential for additional rainfall mid-to-late next  

week, but confidence is very low on if this will cause any hydrologic  

impacts to the region.



.Hawaii...

Considerable flash, urban, and small stream flooding impacts remain  

possible for Niihau and Kauai into Sunday morning as a slow-moving band of  

heavy rainfall moves across the island. Landslides are also possible in  

areas of steep terrain.



.Southeast...

Flash, urban, and small stream flooding impacts, some locally considerable,  

are possible through day 1 (Sat), primarily along central Gulf Coast and FL  

Panhandle, as areas of heavy rainfall progress across the region. Rainfall  

over the past 24 hours has moistened top layer soil columns (65 -75% RSM,  

NASA SPoRT) and elevated streamflows across the region (USGS) ahead of the  

additional rainfall (1 - 2"+), creating efficient runoff conditions and  

potential for rapid rises on smaller tributary rivers across the region.  

The primary flooding threat will likely be across urban areas, but small  

stream flooding impacts cannot be ruled out. The National Water Model (NWM)  

Short Range Forecast (SRF) is signaling potential for isolated rapid onset  

flooding this morning into the afternoon across the FL Panhandle into far  

southwest GA, however, high magnitude river responses are not being  

signaled at this time, which is in line with expectations across the  

region. Isolated minor mainstem river flooding impacts will be possible  

over the next couple days as water routes through the slow to respond river  

systems from southern MS through the FL Panhandle/southwest GA.



.Central Plains into the Upper Midwest...

Multiple days of rain and thunderstorms will introduce a localized threat  

for flooding impacts beginning day 2 (Sun) and continuing through day 5  

(Wed). Each day, the heaviest rainfall totals (1 - 2") are expected to be  

across different basins, limiting the potential for flooding impacts given  

that there is ample soil infiltration capacity available (35 - 60% RSM 0 -  

10cm, NASA SPoRT) and time for recovery between each round of rainfall.  

Nonetheless, streamflows are above climatological normal (USGS), and  

isolated river flooding impacts will be possible across IA, southern MN,  

and WI by mid next week. The GFS and NBM forced NWM Medium Range Forecasts  

suggest potential for isolated small stream flooding impacts across the  

region, but there are not robust forecast signals for widespread riverine  

responses.



.Puerto Rico and USVI...

Periods of heavy rainfall are expected through at least the middle of next  

week across the islands, increasing the potential for flooding impacts.  

Soils across the islands are already very wet given the recent rainfall,  

increasing runoff efficiency, the potential for rapid rises on creeks and  

streams, and landslides in areas of steep terrain. Urban flooding is  

expected.



//JEC



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