textproduct: Charleston

WHAT HAS CHANGED

The Aviation section was updated for the 12z TAF issuance.

KEY MESSAGES

- 1) Hot and humid conditions will continue through Monday, with Sunday temperatures near 100 degrees in some locations. A Heat Advisory is in effect for portions of the area today, and another advisory could be needed Monday.

- 2) A few strong to severe thunderstorms will be possible Sunday evening, with the primary threat area across southeast SC.

- 3) High temperatures will be slightly above normal on Tuesday, then gradually rising through the holiday weekend. Extreme heat is possible during the holiday weekend.

DISCUSSION

KEY MESSAGE 1: Hot and humid conditions will continue through Monday, with Sunday temperatures near 100 degrees in some locations. A Heat Advisory is in effect for portions of the area today, and another advisory could be needed Monday.

Heat and humidity will remain the primary concern across the forecast area through Monday. Sunday continues to look like it will bring the highest temperatures, with widespread upper 90s and a few locations likely reaching 100. Monday is also expected to bring widespread upper 90s. We did make adjustments to dewpoints to blend in some lower values for both days. For Sunday, surface winds should have more of a westerly component than previous days which will have a couple of effects. First, this direction should allow dewpoints inland of the coastal corridor to mix out just a bit more, yielding values in the 69-71 degree range. Also, this westerly component will pin the sea breeze closer to the coast and delay its inland push. Along the coastal counties, dewpoints will remain in the mid and even upper 70s which will result in more coverage of heat indices in the 108-110 degree range. Therefore, we will go with a Heat Advisory for the entire coast. It is a bit marginal concerning the strict 108 degree heat index threshold, but it will certainly be hot and uncomfortable. Looking ahead to Monday, we could need another Heat Advisory and it looks as though the higher heat indices will be a bit further south across southeast GA. Still plenty of time to see how things work out today and make decisions about Monday.

KEY MESSAGE 2: A few strong to severe thunderstorms will be possible Sunday evening, with the primary threat area across southeast SC.

Aloft, the ridge will be centered to the west with a well defined shortwave progged to drop southeastward around the periphery and approach the forecast area. Also, there will likely be an MCV driving morning convection across KY and TN that will track across western NC and into SC in the afternoon hours. Ahead of this feature, model consensus is for little to no development in the absence of any real triggering mechanism. Instead, we will likely have to wait for the evening hours to see any development. When these aforementioned features arrive, the environment should be moderately unstable following temperatures in the upper 90s. Model soundings show mid-level flow as pretty modest in the 20-25 kt range with DCAPE values up to around 1,000 J/kg. So, there will be a risk of damaging wind gusts. The main area of concern looks to be southeast SC and this matches well with SPC's Day 1 Marginal Risk area. The time period of most concern is roughly from 6pm-12am, with some uncertainty on either end of that range.

KEY MESSAGE 3: High temperatures will be slightly above normal on Tuesday, then gradually rising through the holiday weekend. Extreme heat is possible during the holiday weekend.

Strong ridging will persist over the eastern half of the country, with a roughly 596 dam 500 mb High over the TN Valley on Tuesday. It'll shift to our north Wednesday and Thursday, while strengthening slightly. Then, it'll remain in place and gradually weaken Friday through the holiday weekend.

As for temperatures, they'll 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, when they peak in the upper 90s to possibly 100 degrees across our area. Even the beaches should be in the 90s that day. 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, so we may need Heat Advisories for portions of our area.

As for the convective potential, the pattern will only support chance POPs along our GA coast on Tuesday, then dry conditions Wednesday and Thursday, followed by slight chance POPs for portions of our area 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 SUNDAY THROUGH THURSDAY/

The 12z TAF period begins with VFR conditions at KCHS, KJZI, and KSAV. West winds will prevail for much of the day, keeping the sea breeze pinned close to the coast. The sea breeze will first clear KJZI in the early afternoon but will be much later to arrive at KCHS and especially at KSAV. Attention then turns to the potential for thunderstorms this evening. The best chances for direct impacts should be around KCHS and KJZI, but could also extend to KSAV as well. We have maintained the PROB30 for TSRA at KCHS and KJZI and VCSH at KSAV for now. It remains unclear just how far to the southwest storms will extend. Shower and thunderstorm activity should come to an end by the early morning hours.

Extended Aviation Outlook: Brief flight restrictions are possible due to showers and thunderstorms Monday afternoon and maybe Tuesday afternoon.

MARINE

Today through tonight: Southwest flow will mostly prevail today, turning a bit more southerly this afternoon and into the evening with the development of the sea breeze. Winds will surge into the 15-20 knot range this afternoon and evening, with a few 25 knot gusts possible in the Charleston County waters. Through the overnight, southwest flow will remain somewhat elevated through the early morning hours. Seas are expected to be mostly 2-3 feet across most of the waters. Slightly higher seas up to 4 feet will be possible in the Charleston County waters this evening through the early morning hours. Also of note, thunderstorms could develop inland during the evening hours and impact the coast and the coastal waters through the early morning hours with gusty winds and lightning. The best thunderstorm coverage will be possible across the SC waters.

Extended Marine: Expect weak winds on Monday as a front approaches from the north. The front will move south through our area Monday night, causing winds to shift to the NE by Tuesday morning. Then, the synoptic pattern will generally support winds from the NE or E through Thursday. Seas should stay 4 ft or less. No Small Craft Advisories are expected.

Rip Currents: The combination of gusty winds with the afternoon sea breeze and 2-3 ft swell every 8-9 seconds will result in a Moderate Risk of rip currents at all beaches today.

CLIMATE

Record High Temperatures:

June 28: KCHS: 99/1998 KSAV: 100/1998

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

July 3: KCHS: 98/2019

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

Record High Minimum Temperatures:

June 28: KCHS: 78/2013 KCXM: 81/1998

June 29: KCHS: 79/1977 KSAV: 80/1885

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 GAZ137-216>219-238>241. SC...Heat Advisory from noon today to 6 PM EDT this evening for SCZ045-147>152. MARINE...None.