textproduct: NWS Wilmington

WHAT HAS CHANGED

Updated 12Z TAF discussion.

Overnight Update: Minor tweaks have been made to forecast highs over the next few days in-line with the latest NBM. Heat Advisory criteria should still be reached for many areas across eastern North and South Carolina over the next few days.

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.

An anomalously strong 500 mb ridge currently centered over the TN mountains should slide a bit eastward over the next 48 hours. Forecast 500 mb heights of 5940-5950 meters are 20-30 meters above the climatological 90th percentile for the Morehead City and Charleston upper air sites and could approach daily record observed values. Beneath this powerful ridge aloft, subsidence will warm and dry the mid levels out producing a convective cap above the hot and humid boundary layer.

Forecast highs in the mid to upper 90s are only 1-4 degrees below records at many locations for the remainder of this week. When combined with dewpoints in the 70s, heat indices should reach 103 to 108 degrees each day through Saturday.

Daily record highs through Saturday... Location...........Wed 9/2.....Thu 9/3......Fri 9/4......Sat 9/5 Wilmington.......96 in 1912...97 in 2010..100 in 1925...95 in 2023 N Myrtle Beach...98 in 1932...97 in 1944...99 in 1944...98 in 1944 Florence.........99 in 2014...98 in 2010...99 in 1954..100 in 1954 Lumberton.......101 in 1912..100 in 1926..104 in 1925..100 in 1954

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

Relief from the heat should begin to arrive Saturday. An impressive upper trough over the Canadian Maritime provinces should lower heights along the U.S. East Coast, forcing the upper ridge to retrograde to the lower Mississippi Valley on Saturday and the central Plains states by Sunday. Strengthening mid and upper level NW flow along the East Coast should help push a cold front southward and into the Carolinas on Saturday. Models have been rather consistent for the past few days showing the front arriving late in the afternoon or evening hours and accompanied by clusters of showers and thunderstorms.

SPC's current extended outlook does not include severe probabilities for Saturday this far south, however steep lapse rates and 20-25 knots of 0-6 km bulk shear should provide some convective organization along the cold front. NCAR Medium-range AI Convective Hazard Forecasts shows some low-end severe probabilities across portions of North and South Carolina Saturday.

The front should shift farther south into South Carolina on Sunday -- still close enough for scattered showers and thunderstorms to continue. By Monday the weakening front may be south of the Savannah River with drying conditions developing for our area.

AVIATION /10Z WEDNESDAY THROUGH SUNDAY/

VFR outside of possible ground fog early this morning. Dry conditions during the day with possible mist/ground fog again Wednesday night.

Extended Outlook...Areas of ground fog are possible late tonight and again Thursday night. Thunderstorms should become numerous across the area Saturday afternoon into Saturday evening as a cold front arrives from the north.

MARINE

Through Monday...Bermuda high pressure should provide light south to southwesterly winds and dry weather again today and Thursday. By Friday the high will begin to retreat offshore as a cold front advances southward down the East Coast. The increasing pressure gradient between the high and the front should lead to an uptick in wind speeds Friday and the development of choppier seas. On Saturday the front should arrive during the afternoon or evening accompanied by multiple waves of showers and thunderstorms. Gusty winds and frequent lightning are possible.

Models suggest the front should continue to move southward across southern South Carolina on Sunday, still close enough for scattered showers or thunderstorms to continue.

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.