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AGUS74 KWCO 261149
HMDNWC

National Hydrologic Discussion - EXPERIMENTAL
NWS National Water Center - Tuscaloosa AL
700 AM CDT SAT SEP 26 2026

.Update...
For this mornings issuance of the Flood Hazard Outlook (FHO), the only
notable change made was to the Days 1-3 Limited selection in the Desert
Southwest, which is now a Days 1-7 Limited to account for possible
lingering QPF in the medium range.

No other significant changes were made to the FHO.

//Ducre

Previous discussion is as follows

...Considerable to locally catastrophic flash flooding possible in Hawaii...
Flash flooding impacts remain possible across portions of the Southwest...
Flash and urban flooding possible in the Northeast... Moderate to major
coastal flooding expected along the Coastal Mid-Atlantic... Flash and river
flooding impacts possible for the Central Plains into the Middle
Mississippi Valley...

.Hawaii...
Locally catastrophic flooding impacts remain possible for the southern and
eastern portions of the Big Island today through Saturday with considerable
impacts remaining possible through the weekend as Hurricane Nolo is
forecast to produce 10 - 15" with a maximum of 25" possible. Previous days
of heavy rainfall have continued to increase the hydrologic sensitivity of
these areas, supporting increased confidence in considerable impacts,
including life-threatening flash flooding along with mudslides in areas of
steep terrain. The rest of the Big Island and Maui County remain in a
Limited selection due to the possibility of locally considerable impacts
through the weekend. Hurricane Nolo is forecast to produce 2 - 4" with
isolated 8" possible for the western and northern portions of the Big
Island, while forecast totals for Maui County are 4 - 6" with isolated 10"
possible. No changes were made to the existing Limited and Considerable
areas across the Big Island and Maui County for the afternoon issuance.

.Southwest...
Flash flooding impacts remain possible for portions of southern and eastern
New Mexico as well as portions of far west Texas into the Texas and
Oklahoma Panhandles through Saturday morning as yet another surge of
monsoonal moisture brings repeated thunderstorms and heavy rainfall.
Portions of southeastern New Mexico have already seen multiple days of
heavy rainfall this week, which has greatly increased the hydrologic
sensitivity of these basins. The greatest forecast rainfall amounts remain
along and east of the Sacramento Mountains, where soil moisture has not had
much time to recover from rainfall during the last 24 hours. The wetter
soils conditions across the majority of the area of concern continue to
support the likelihood of stronger hydrologic responses including rapid
response runoff. Rapid runoff remains possible in small creeks, streams,
dry washes, along with debris flows near burned areas and steep terrain.
Antecedent conditions are only slightly drier in far west Texas, but
successive days of rainfall have increased soil moisture and also decreased
the time it could take for soils to become overwhelmed and initiate
efficient runoff and quick rises on small streams. The GFS and NBM-forced
National Water Model are in agreement with possible rapid onset flooding
impacts across the area of concern, particularly in eastern New Mexico, but
the isolated nature of signals has lowered confidence on exact placement of
greatest impacts.

After a short break in precipitation over the weekend, rain chances return
early next week with another substantial surge of monsoonal moisture. Given
the increased hydrologic sensitivity of the area, particularly in southern
and eastern New Mexico, the situation will continue to be monitored over
the weekend for changes in the forecast.

.Coastal Mid-Atlantic...
Moderate to major coastal flooding is expected to continue along portions
of the Mid-Atlantic coastline from North Carolina to Connecticut into this
weekend as a result of astronomical high tides and the Noreaster
generating onshore flow to the region.

.Northeast...
Flash and urban flooding is possible this weekend and into early next week
as the Nor`easter moves into the region. Widespread rainfall totals of 3 -
5" are expected with locally higher amounts possible, and models generally
agree on rainfall placement and magnitude which increases confidence in
flooding impacts in the region. Isolated river flooding is also possible
over portions of New Jersey and eastern Pennsylvania.

.Central Plains and the Middle Mississippi Valley...
Flash and river flooding impacts are possible starting next week as the
region receives several rounds of heavy rainfall over the next several
days. Antecedent conditions in eastern Nebraska and western Iowa are fairly
saturated, so the repeated rounds of rainfall are more likely to generate
rapid runoff. This cumulative rainfall also increases the river flood
threat later in the forecast period. Additionally, models generally agree
on placement of the greatest rainfall totals. Guidance from both the GFS
and NBM-forced NWM shows probabilities of rapid onset flooding within the
next 10 days. The NWM also shows widespread annual exceedance probabilities
of 50-20%, with some areas in Kansas seeing 10-2% probabilities, suggesting
the potential for out of bank flows.

//Cordak/EAS

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