textproduct: NWS Wilmington

WHAT HAS CHANGED

Forecast shower and thunderstorm chances have decreased today north of Georgetown and Williamsburg counties.

KEY MESSAGES

1) Shower and thunderstorm chances will shift from the SC Lowcountry today back into northeastern South Carolina and southeastern North Carolina Sunday into Monday.

2) Drier weather is expected from Tuesday through Thursday, but with increasing temperatures and potential for the heat index to exceed 105 degrees.

DISCUSSION

KEY MESSAGE 1...Shower and thunderstorm chances will shift from the SC Lowcountry today back into northeastern South Carolina and southeastern North Carolina Sunday into Monday.

A slug of dry mid level air associated with the Bermuda ridge offshore should lead to a lower potential for showers and thunderstorms across our portion of the eastern Carolinas today. This dry air shows up quite well in model precipitable water plots which have PW values falling as low as 1.4 inches today. This is near the 25th percentile for early August and is as much as 1.0 inches lower than we saw just a few days ago.

Just to the south of this ribbon of dry mid level air will be much richer moisture values extending across Florida, Georgia, and into southern South Carolina. HREF PoP/QPF plots show the northern edge of this moisture could draw close enough to the Santee River for some scattered showers and storms to develop there today, potentially affecting Georgetown and Kingstree but likely remaining south of Myrtle Beach. Forecast PoPs range from 20-40 percent today across Georgetown and Williamsburg counties, but generally 0-10 percent across the Cape Fear area and northern Pee Dee regions.

The center of the Bermuda ridge should sink south Sunday into Monday, allowing veering mid level wind directions and increasing Gulf moisture across the area. Precipitable water values should climb back toward 2.0 inches by late Sunday and should rise even further on Monday. This should set the stage for increasing coverage of showers and thunderstorms, especially Monday.

KEY MESSAGE 2...Drier weather is expected from Tuesday through Thursday, but with increasing temperatures and potential for the heat index to exceed 105 degrees.

The mid and upper level ridge will begin to retrograde westward across Florida and into the eastern Gulf by the middle of next week. Westerly downsloping flow over the southern Appalachians should push our 850 mb temps above +20C each day beginning Tuesday. This should equate to highs in the 93-97 degree range. Add in seasonably high dewpoints well into the 70s and it's possible heat indices will exceed 105 degrees beginning Tuesday. A Heat Advisory may be needed each day.

AVIATION /06Z SATURDAY THROUGH WEDNESDAY/

Early morning fog and low ceilings is the primary weather concern. Calm surface winds, seasonably high dewpoints, and mainly clear skies aloft have set the stage for fog. Recent hourly statistical models suggest visibility should begin to drop at KFLO between 08-10z, with IFR vis and/or ceilings possible between 10-13z. Confidence in impacts is high, although confidence in timing is only moderate. KLBT should have largely the same conditions, although statistical guidance is not as bullish about IFR impacts as they are at KFLO.

Ceiling and visibility should both become VFR after 13z. Afternoon convection appears it may be more limited in coverage today than we've seen over the past several days, mainly due to dry mid level conditions courtesy of the Bermuda high offshore. There is a low potential convection may develop in the vicinity of KMYR or KFLO during the daylight hours, but not enough confidence for any mention in the TAFs.

Extended Forecast...Increasing moisture should fuel scattered showers and thunderstorms Sunday, with an even larger coverage of storms expected Monday. Hotter weather is expected for the middle of next week with isolated showers and thunderstorms still possible. Late night/early morning low ceilings are possible day, especially inland, affecting the KFLO and KLBT airports.

MARINE

Bermuda high pressure offshore should remain the dominant weather maker for us over the next five days. The center of the high is currently between Bermuda and Cape Fear, close enough to limit today's coverage of showers and thunderstorms for areas north of Myrtle Beach. The high should sink south next week, leading to winds veering more westerly and increasing in speed. We also should experience a larger number of showers and thunderstorms Sunday and especially Monday.

ILM WATCHES/WARNINGS/ADVISORIES

NC...None. SC...None. MARINE...None.