textproduct: NWS Wilmington

WHAT HAS CHANGED

Changes between this forecast package and the previous one are minor. Unseasonable heat today and Saturday and severe weather potential Saturday afternoon/evening remain the biggest concerns.

KEY MESSAGES

1) Well above normal temperatures and humidity will bring triple digit heat indices again today and Saturday. A Heat Advisory is in effect today.

2) A cold front will bring 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 again today and Saturday. A Heat Advisory is in effect today.

The powerful mid and upper level ridge will spend one more day anchored over North and South Carolina before retreating westward on Saturday as a trough sweeps across the northeastern quarter of the country. Today's forecast atmospheric parameters are little changed from yesterday and argue for a day just as hot as we saw Thursday:

- 500 mb heights (5920 meters) about 10 meters above the 90th percentile for Greensboro - 850 mb temps peaking at +21 to +22C by late afternoon, about 3C above the 90th percentile for Greensboro

Forecast highs are in the 94-97 range inland with upper 80s to around 90 expected on the beaches.

Although upper level heights should fall on Saturday, westerly 850 mb flow just ahead of the approaching cold front should maintain very hot weather. Saturday may be the hottest day of the week at the coast since westerly flow will restrict the seabreeze and forecast highs are in the 90s everywhere including the beaches. Our forecast for Wilmington, if correct, would break a record set back in 2023.

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

KEY MESSAGE 2...A cold front will bring showers and thunderstorms this weekend, followed by cooler temperatures early next week.

Warm subsidence aloft beneath the upper ridge should maintain dry weather today through early Saturday afternoon. 500 mb heights should fall by 30-40 meters between 5 PM today and 5 PM Saturday, accompanied by a 1.5 to 2C fall in 700 mb temps as the subsidence inversion fades. While these changes occur aloft, the surface cold front should advance farther south through North Carolina, likely igniting multiple clusters of thunderstorms during the afternoon. Mid level flow should tend to push these storms southeastward, impacting our area during the late afternoon and evening hours.

Bulk shear 0-6 km increasing to 25 knots, CAPE exceeding 3000 J/kg, and steep 0-3 km lapse rates argue for damaging winds to be the primary risk with Saturday's storms. I envision multiple clusters of storms moving across the area with bowing line segments producing strong, possibly severe, wind gusts.

The front should stall across South Carolina on Sunday, likely serving as the focus for additional showers and thunderstorms. Canadian high pressure pushing southward on Monday should nudge the front into northern Florida, but the low level E/NE wind crossing water temps in the mid 80s offshore won't necessarily feel refreshing or even like an airmass change.

AVIATION /06Z FRIDAY THROUGH TUESDAY/

The most significant aviation weather concern in the near-term is the development of ground fog inland affecting the KLBT and KFLO airports. Fog has a good potential to become dense at KFLO before daybreak. This fog layer should remain very thin and will likely burn off completely before 13z. Of lesser concern, shortwave IR satellite shows bands of low cumulus clouds moving NW toward the South Carolina beaches. These clouds have a moderate potential to bring periodic MVFR ceilings and maybe even some sprinkles of rain to KCRE and KMYR through 09z.

VFR conditions are expected throughout the day and into tonight. Southerly seabreeze winds along the coast could increase to near 12 knots this afternoon.

Extended Outlook...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 and briefly strong winds is expected Saturday evening. Prevailing VFR conditions should return by Monday and Tuesday.

MARINE

Through Tuesday...The Bermuda High has provided very light winds across the Carolinas for most of the week. Falling pressures in the vicinity of a cold front dipping south across PA and the southern Great Lakes will begin to erode the northern portion of the Bermuda High today and tonight. The high should weaken substantially on Saturday as the front drops into North Carolina.

The net effect of this will be increasing wind speeds this afternoon, then directions veering more westerly in advance of the front Saturday. A line of rather hefty thunderstorms may develop along the front late Saturday afternoon into Saturday evening. Gusty winds and frequent lightning are possible. Scattered showers and maybe a few more thunderstorms could linger behind the front Sunday.

Sunday night and Monday should feature increasing easterly winds as Canadian high pressure builds south along the U.S. East Coast. Wind speeds should increase to 15-20 knots with seas peaking at 6 feet in the 20-60 mile offshore waters, and 4-6 feet inside 20 miles Monday afternoon into Monday evening.

ILM WATCHES/WARNINGS/ADVISORIES

NC...Heat Advisory from 11 AM this morning to 8 PM EDT this evening for NCZ087-096-099-105>110. SC...Heat Advisory from 11 AM this morning to 8 PM EDT this evening for SCZ017-023-024-032-033-039-054>056-058-059. MARINE...None.