textproduct: Charleston

WHAT HAS CHANGED

The Aviation section has been updated for the 12z TAF issuance.

KEY MESSAGES

- 1) Hot and humid conditions are expected to occur again today. A Heat Advisory is in effect for portions of the area.

- 2) High temperatures will be slightly above normal on Tuesday, then gradually rising through the holiday weekend. Heat Advisories could be needed during the holiday weekend across portions of our area.

DISCUSSION

KEY MESSAGE 1: Hot and humid conditions are expected to occur again today. A Heat Advisory is in effect for portions of the area.

Aloft, the forecast area will continue to sit on the eastern periphery of prominent upper ridging and an anticyclone that will lift into the TN Valley. At the surface, a weak boundary will push southward across the area as high pressure centered off the New England coast attempts to nose southward. The surface flow pattern will be considerably different than it was yesterday, much weaker and beginning the day light and out of the north-northwest. Winds should then remain rather weak and out of the northwest for much of the area, except along the coast where the sea breeze will start to take over in the afternoon. The result is a setup that won't favor as much mixing out of dewpoints and allow for greater coverage of low to mid 70s values, especially along the coast and along and south of I-16. This should crossover well with expected temperatures and provide the best chance of seeing heat index values reaching 108 degrees in these areas. Outside of this area, heat indices to around 105 will be more common.

However, the situation is complex as the model consensus for the greatest coverage of diurnal convection should coincide with this area of highest potential heat index. The plan will be to go with a Heat Advisory for southeast GA south of I-16 as well as Beaufort and coastal Jasper counties. If convection then develops early enough to disrupt peak heating and peak heat index values, the advisory could be cancelled early. Concerning convection, the most likely scenario is for typical pulse summertime thunderstorms that are mostly sub- severe. Model soundings do show some potential for elevated DCAPE values (>1,000 J/kg) is a very weakly sheared environment. A strong to marginally severe storm or two is possible, especially where more significant boundary collisions occur.

KEY MESSAGE 2: High temperatures will be slightly above normal on Tuesday, then gradually rising through the holiday weekend. Heat Advisories could be needed during the holiday weekend across portions of our area.

Strong ridging will persist over the eastern half of the country on Tuesday, with a roughly 596 dam 500 mb High over the TN Valley. This is at least 2 standard deviations above normal per NAEFS. This High will shift to our north Wednesday and Thursday, while strengthening slightly. Then, it'll remain in place and gradually weaken late Friday through the holiday weekend.

The combination of rising heights and increasing 850 mb temperatures will cause very hot and humid conditions to settle over our region. High temperatures will be slightly above normal on Tuesday, generally in the lower to middle 90s. Then, they'll increase about 1-2 degrees each day through the end of the week. It appears the hottest temperatures could be on the 4th of July or Sunday, when they peak in the upper 90s to possibly 100 degrees across our area. Even the beaches should be in the 90s both of those days. Combined with dew points in the 70s near the coast and the upper 60s far inland, and we could have heat indices well into the 100s across our entire area Friday into the holiday weekend. Heat indices could peak in the 105-110 degree range on the 4th of July and Sunday, so we may need Heat Advisories for portions of our area.

As for the convective potential, the pattern will only support slight chance to chance POPs along our GA coast on Tuesday, then dry conditions Wednesday and Thursday, followed by POPs gradually trending higher Friday into the holiday weekend. Even though POPs are not very high, any convection that forms this time of year, especially with these temperatures, will have the potential to be strong to borderline severe, along with having locally heavy rainfall.

AVIATION /12Z MONDAY THROUGH FRIDAY/

The 12z TAF period begins with VFR conditions at KCHS, KJZI, and KSAV. The main forecast concern is the potential for afternoon thunderstorms. Model consensus continues to be for most shower and thunderstorm activity to develop to the southwest of KCHS and KJZI, meaning that KSAV would have the best chance of seeing direct impacts. We have transitioned the PROB30 to a TEMPO group for MVFR conditions in thunder from 20-23z.

Extended Aviation Outlook: VFR.

MARINE

Today through tonight: Overall, quiet conditions expected across the local waters. Northwest flow is expected in the morning, weakening and then taking on the sea breeze circulation in the afternoon and evening. Wind speeds should mostly top out in the 10-15 knot range. Overnight, strengthening northeast flow should spread in with speeds getting up to around 15 knots by sunrise Tuesday. Seas are expected to average 2-3 feet.

Extended Marine: The synoptic pattern will generally support winds from the NE or E through Thursday. Then, they will clock around to the SW by Friday morning. Friday into the holiday weekend, winds will have a typical summertime pattern. This will consist of some backing during the day, with the highest winds along the land/sea interface with the formation of the sea breeze. Gusts could approach 20 kt, especially in Charleston Harbor as the sea breeze moves through. At night, expect winds to veer and possibly ease a few kt. Seas should stay 5 ft or less. No Small Craft Advisories are expected.

CLIMATE

Record High Temperatures:

June 29: KCHS: 99/1998 KSAV: 101/1959

July 4: KCHS: 98/2023 KSAV: 99/1997

Record High Minimum Temperatures:

July 3: KCHS: 78/2016

July 4: KCHS: 79/2016 KSAV: 79/1931

CHS WATCHES/WARNINGS/ADVISORIES

GA...Heat Advisory from noon today to 6 PM EDT this evening for GAZ114-115-137-216>219-238>241. SC...Heat Advisory from noon today to 6 PM EDT this evening for SCZ148-151. MARINE...None.