textproduct: NWS Wilmington

WHAT HAS CHANGED

Few changes have been made with regard to heat today through Saturday or with thunderstorm chances Saturday/Saturday night. Uncertainty appears to have increased with regard to how great the chance of post-frontal showers and t-storms will be on Sunday.

KEY MESSAGES

1) Well above normal temperatures and humidity will bring triple digit heat indices through Saturday.

2) A cold front will result in increased chances for showers and thunderstorms this weekend, followed by cooler temperatures early next week.

DISCUSSION

KEY MESSAGE 1...Well above normal temperatures and humidity will bring triple digit heat indices through Saturday.

Models have remained remarkably consistent with their forecast strength of the 500-700 mb ridge centered over the Carolinas. NAEFS climatology suggests 500 mb heights are in excess of the 99.5th percentile across central NC today, a figure largely supported by the SPC Sounding Climatology website.

850 mb temps of +20 to +22C are also well above normal for early September and should support high temps in the mid 90s with some upper 90s possible across Darlington, Hartsville, and Bennettsville. When combined with high dewpoints, many areas will contend with heat indices near or above 105 degrees again today and a Heat Advisory remains in effect.

Unseasonable heat should continue for two more days before a cold front, pushed southward by a trough digging across the northeastern US, brings somewhat cooler air in from the north.

Daily record highs through Saturday... Location...........Thu 9/3......Fri 9/4......Sat 9/5 Wilmington.......97 in 2010..100 in 1925...95 in 2023 N Myrtle Beach...97 in 1944...99 in 1944...98 in 1944 Florence.........98 in 2010...99 in 1954..100 in 1954 Lumberton.......100 in 1926..104 in 1925..100 in 1954

Climate Note: If our forecast verifies Sep 1-5 will all have high temps in Wilmington of 92 degrees or higher. By itself this will move 2026 into 6th place for the most number of 92+ degree September days in Wilmington.

KEY MESSAGE 2...A cold front will result in increased chances for showers and thunderstorms this weekend, followed by cooler temperatures early next week.

The strong mid and upper level ridge across the Carolinas is supporting a deep layer of dry air aloft and a thermodynamically stable subsidence inversion between 7k-10kft. These two factors should keep chances for pop-up convection below 10 percent today through early Saturday afternoon.

Models have been very consistent for several days showing an upper low currently centered across Quebec moving southeastward on Saturday across New Brunswick and Prince Edward Island. As this trough drops in, falling heights along most of the U.S. East Coast will force the upper ridge to retrograde into the central Plains states. With the erosion of the subsidence inversion over the Carolinas, the arrival of a surface cold front, and northwesterly 700 mb flow increasing to 20-25 kt, chances for waves of showers and thunderstorms are growing starting late Saturday afternoon.

SPC is in agreement with latest NCAR-hosted AI/NN hazard outlooks that a chance of severe thunderstorms may exist across our area Saturday. Northwesterly flow aloft and 0-6 km bulk shear around 25 knots argues for a wind threat assuming upstream convection across northern and central North Carolina can organize large cold pools.

Confidence in shower and thunderstorm coverage on Sunday is low given a wider spread in where models show the front. The 00z GFS blows the boundary clear past the Savannah River on Sunday while the Canadian keeps it across South Carolina. NBM ensemble blends favor the slower solution and Sunday's forecast PoPs will remain in the 40-70 percent range. Drier weather should arrive by Monday.

AVIATION /06Z THURSDAY THROUGH MONDAY/

VFR conditions are expected at all local airports over the next 24 hours with the exception of a low-end potential for ground fog between 10-13z.

Extended Outlook...There is a moderate to high potential for ground fog late tonight across most of the area. Showers and thunderstorms should become numerous across the area late Saturday afternoon through Sunday as a cold front arrives from the north. The highest potential for IFR conditions in convection is expected Saturday evening. Prevailing VFR conditions should return by Monday.

MARINE

Through Monday...Today should be our last day of light south to southeast winds under Bermuda High Pressure. On Friday the high will begin to retreat offshore as pressures lower to our north in advance of an approaching cold front. This tightened pressure gradient should lead to increasing south to southwest winds Friday afternoon, likely exceeding 15 knots north of Cape Fear.

Moderate west to southwest winds are expected Saturday up until the cold front arrives during the evening. This front should be accompanied by gusty thunderstorms that may sweep rapidly offshore Saturday night. There are still questions as to how far south the front moves on Sunday, but it appears to remain near enough to the area for good chances for showers or thunderstorms to continue, especially south of Cape Fear. Drier weather should arrive on Monday.

ILM WATCHES/WARNINGS/ADVISORIES

NC...Heat Advisory from 11 AM this morning to 8 PM EDT this evening for NCZ087-096-099-105-107-109. SC...Heat Advisory from 11 AM this morning to 8 PM EDT this evening for SCZ017-023-024-032-033-058-059. MARINE...None.