961
FXUS21 KWNC 231831
PMDTHR
US Hazards Outlook
NWS Climate Prediction Center College Park MD
300 PM EDT September 23 2024

SYNOPSIS: At the beginning of week-2, there are considerable model differences
regarding the remnants of Potential Tropical Cyclone Nine which is forecast to
impact the southeastern contiguous U.S. (CONUS) during week-1. Possibilities
range from dissipation to a more consolidated system lingering near the Eastern
Seaboard. Above-average temperatures and a more tranquil pattern are forecast
elsewhere across the CONUS. Alaska is forecast to be in between significant
weather systems at the beginning of week-2, with chances for hazardous
precipitation and winds potentially increasing across the southern part of the
state by the second half of the period.

HAZARDS

Slight risk of heavy precipitation across portions of the Southeast, Tennessee
Valley, Central and Southern Appalachians, and Mid-Atlantic, Tue-Thu, Oct 1-3.

Flooding possible across portions of the Southeast.

Risk of Rapid Onset Drought across portions of eastern Oklahoma and
northeastern Texas.

DETAILED SUMMARY

FOR THURSDAY SEPTEMBER 26 - MONDAY SEPTEMBER 30:
https://www.wpc.ncep.noaa.gov/threats/threats.php

FOR TUESDAY OCTOBER 01 - MONDAY OCTOBER 07: As of 2pm EDT today, the National
Hurricane Center (NHC) forecasts Potential Tropical Cyclone Nine (PTC-9) to
intensify into a hurricane before striking the Gulf Coast later this week.
While direct coastal impacts are expected to end prior to the start of the
week-2 forecast period, the remnant circulation is forecast to meander inland
across the Southeast. Dynamical models depict differing scenarios, with the 0z
GEFS indicating a faster dissipation of the system with minimal impacts during
week-2 and the 0z ECENS maintaining a more coherent circulation near the
Eastern Seaboard. This is also reflected in the ECENS Probabilistic Extremes
Tool (PET) which depicts a 20 percent chance of 3-day precipitation totals
exceeding the 85th climatological percentile and 1-inch early in week-2 over
parts of the East. Both models also indicate shortwave troughing moving into
the eastern CONUS which may also lead to increased cyclonic flow across the
region. Given the synoptic pattern, more robust precipitation forecast in the
ECENS, and continuity from last week, a slight risk for heavy precipitation is
posted across portions of the Southeast, Central and Southern Appalachians, and
the Mid-Atlantic, Oct 1-3. There is more uncertainty than usual, especially
given any changes to the track forecast of PTC-9 could have implications for
the forecast evolution later in week-1 into week-2.



Flooding is possible across portions of Alabama, Georgia, and Florida in the
wake of PTC-9 and consistent with high week-1 projected rainfall totals from
the Weather Prediction Center (greater than 4-inches over some areas). Heavy
rainfall is also forecast to expand westward toward the Middle Mississippi and
Ozarks, which should mitigate the drought concerns in that region, but may also
need to be monitored for flooding as well. Antecedent heavy rainfall across
western and central portions of Oklahoma also favor decreased chances of
drought development in that area. Therefore, only portions of eastern Oklahoma
and northeastern Texas remain at elevated risk for rapid onset drought
development where precipitation deficits of around 3-inches remain and
below-normal precipitation is forecast during week-2.



A frontal system is forecast to move across the Northern Plains and Upper
Midwest toward the end of week-1, bringing in a period of relatively cooler
temperatures. The GEFS and ECENS PETs indicate at least a 40 percent chance of
minimum temperatures falling below 40 deg F over some areas, and frost cannot
be ruled out over susceptible vegetation. However, since the prevailing
temperatures are still forecast to be above-normal, no related below-normal
temperature hazards are posted. The ECENS PET also depicts at least a 20
percent chance wind speeds exceed the 85th climatological percentile and 20-mph
early in week-2. However, the best synoptic set-up is on day-7 tied to the
frontal passage, and no related wind hazard is highlighted over the region.



Surface low pressure is forecast across the Aleutians and Gulf of Alaska late
in week-1 bringing the potential for high winds and heavy rain across the
southern coast of the state. This system is forecast to weaken at the outset of
week-2, with another area of surface low pressure taking a similar track across
the region toward the middle of the period. Given that Alaska is likely to be
in-between these two weather systems at the start of week-2, no related hazards
are indicated. However, wind and precipitation hazards may need to be
considered related to the second system, but holding off for now given the
weaker depiction of the surface low in the GEFS relative to the ECENS and CMCE.

FORECASTER: Thomas Collow

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