Composite Map Day 8-14

Experimental Probabilistic Outlooks Temperature Hazards Precipitation Hazards Wind Hazards Snow Hazards

Valid Friday September 27, 2024 to Thursday October 03, 2024

US Hazards Outlook
NWS Climate Prediction Center College Park MD
300 PM EDT September 19 2024

Synopsis: Model solutions indicate increasing tropical convection and the potential for tropical cyclone (TC) development over the western Caribbean, resulting in an enhanced chance for heavy precipitation for portions of the Southeast U.S. Mid-level low pressure over the Aleutian Islands and a series of surface low pressure systems bring the potential for episodic heavy precipitation to southeastern Alaska and high winds along the southern and southeast coasts. Large precipitation deficits over the last few weeks, combined with expected warm, dry weather results in the risk for Rapid Onset Drought (ROD) for portions of the Southern Plains and Ozarks.

Hazards

• Moderate risk of heavy precipitation for northern and central Florida, much of Alabama and Georgia, and portions of South Carolina, Fri-Sun, Sep 27-29.
• Slight risk of heavy precipitation for the Southeast U.S. as well as portions of the Tennessee and Lower Mississippi Valleys, Fri-Tue, Sep 27-Oct 1.
• Slight risk of heavy precipitation for portions of southeastern Alaska, Fri-Tue, Sep 27-Oct 1.
• Slight risk of high winds for Florida, coastal portions of Alabama, Mississippi, and eastern Louisiana, as well as portions of southern Georgia, Fri-Sun, Sep 27-29.
• Slight risk of high winds for the southern and southeast coast of Alaska, Fri-Tue, Sep 27-Oct 1.
• Risk of Rapid Onset Drought for portions of the Southern Plains and Ozarks.

Detailed Summary

For Sunday September 22 - Thursday September 26: WPC Days 3-7 U.S. Hazards

For Friday September 27 - Thursday October 03: The highlight for the week-2 hazards outlook continues to be the potential for TC activity in the western Caribbean. Forecast uncertainty remains high regarding the timing and location, but model ensembles continue to show with fairly high confidence that some sort of system is likely to form and affect the Gulf Coast. It is still too early to determine the potential intensity of an emerging storm, but models are consistently depicting the potential for copious precipitation over much of the Southeast U.S. during week-2. The GEFS and ECMWF Probabilistic Extremes Tools (PETs) continue to indicate at least a 20% probability of 3-day precipitation exceeding the 85th percentile and at least 1 inch for much of the Southeast U.S. for much of the forecast period. The ECMWF is especially bullish, extending 3-day 1 inch totals all the way up the Eastern Seaboard and higher probabilities of exceeding the 85th percentile for the Southeast U.S., as well as highlighting the potential for over 2 inches for portions of Florida, Alabama, and Georgia early in week-2. Therefore a moderate risk of heavy precipitation is posted for northern and central Florida, much of Alabama and Georgia, and portions of South Carolina for Sep 27-29, and a larger slight risk of heavy precipitation is posted for the Southeast U.S. as well as portions of the Tennessee and Lower Mississippi Valleys for Sep 27-Oct 1. A slight risk of high winds is also highlighted for Florida, coastal Alabama, and southern Georgia for Sep 27-29.

There is good consensus among multiple model ensembles with regard to an amplified mid-level trough over the Aleutian Islands in place at the start of week-2 and a series of surface low pressure systems moving into the southeastern Alaska coast, bringing periods of heavy precipitation with them. This is supported by the ECMWF and GEFS PETs, which indicate the potential for 3-day precipitation totals to exceed 3 inches for portions of the panhandle of Alaska for much of week-2. Uncertainty increases later in the forecast period so for now a slight risk of heavy precipitation is posted for the southern coast and Panhandle of Alaska for Sep 27-Oct 1. Today’s model solutions feature stronger surface lows moving onshore, bringing enhanced potential for strong winds all along the southern coast of Alaska, including the potential for gap winds along the Alaska Peninsula. Therefore a slight risk of high winds is posted for the southern and southeast coast of Alaska for Sep 27-Oct 1.

A large area of the Southern Plains, including portions of northern Texas, eastern Oklahoma and western Arkansas have been experiencing very dry conditions for the last month, with precipitation deficits exceeding 3 inches in some locations. This has led to drying soils, a situation likely to be exacerbated by above-normal temperatures that are expected for the next few weeks and little precipitation, especially in week-2. Given these conditions the risk for ROD is highlighted for central and eastern Oklahoma, as well as portions of northern Texas and western Arkansas.

Forecaster: Danny Barandiaran

$$ Please consult local NWS Forecast Offices for short range forecasts and region-specific information.

Resources

Week-2 Probabilistic Extremes Tool

GFS Ensemble Forecasts