textproduct: Charleston

WHAT HAS CHANGED

The aviation section was updated for the 12z TAFs

KEY MESSAGES

- 1) Above-normal temperatures and below-normal rain chances are expected through the upcoming weekend.

- 2) Temperatures likely to approach the triple digits this weekend. Heat Advisories could be needed.

DISCUSSION

KEY MESSAGE 1: Above-normal temperatures and below-normal rain chances are expected through the upcoming weekend.

Early morning surface observations and stability analysis shows a backdoor cold front has pushed south of the Santee River and will continue to meander south through the South Carolina Lowcountry and into Southeast Georgia this morning. The front is expected to stall out somewhere in the vicinity of the Altamaha River by noon with relatively cooler and drier air advecting into the region. Guidance is similar in showing a modest pure sea breeze circulation developing later today which will propagate steadily inland through the afternoon. While modified soundings show a pronounced capping inversion holding in place away from the coast through the day, weak to modest instability (MLCAPE 1000-1400 J/kg, lifted indices -2C to -4C) is progged to develop by mid-late afternoon along the Georgia and far southern South Carolina coast as dewpoints surge with the passage of the sea breeze. Despite the dry mid-levels, there looks to be enough low-level theta-e advection and boundary layer convergence within the sea breeze circulation itself to support pockets of isolated convection, roughly aligned along a Beaufort-Savannah-Hinesville-Ludowici corridor. The presence of extensive mid-level dry air will keep updrafts weak and fairly transient due to dry air entrainment, but there is a reasonable signal for some measurable rainfall within the noted corridor. Pops 20-30% were introduced into these areas with pops <10% elsewhere. Temperatures this afternoon will warm into the upper 80s/lower 90s away from the coast with lower-mid 80s at the beaches. Quiet, rain-free conditions will prevail overnight with lows from the upper 60s/lower 70s inland to the upper 70s at the beaches.

Atlantic high pressure will extend westward across the forecast area and into the Gulf. Aloft, a building ridge and increasing subsidence will limit convection through the weekend. Relatively dry low and mid-level air will persist through Thursday, further suppressing convection, with only the potential for a stray shower or two south of the Savannah River. Otherwise, no more than isolated shower or thunderstorm activity expected Friday through Sunday.

KEY MESSAGE 2: Temperatures likely to approach the triple digits this weekend. Heat Advisories could be needed.

A gradual warming trend is forecast through the remainder of the week and into the weekend. High temperatures in the lower 90s Wednesday will rise a couple of degrees each day, with upper 90s common across much of the area Saturday and Sunday. A few locations could even exceed 100 degrees on Sunday. Combined with dew points in the 70s, heat index values could reach 108-113F Sunday, especially across the coastal counties. Additionally, being that convection is forecast to be isolated, we do not expect much cooling/relief from showers/storms. While confidence in the magnitude of the heat as well as the convective coverage remains limited given the forecast range, the combination of extreme heat, high humidity, and limited cooling could necessitate Heat Advisories where heat indices meet or exceed our local criteria of 108F degrees. Forecast trends will continue to be monitored over the coming days.

Additionally, records will be challenged this weekend, mainly the high minimum temperatures. Although, on Sunday record highs could be reached. See the Climate section below for details.

AVIATION /12Z WEDNESDAY THROUGH SUNDAY/

24/12z TAF Discussion: KCHS/KJZI/KSAV: VFR through 25/12z. There is a low-end risk for tstm impacts at KSAV by late afternoon as isolated shower/tstms possibly form near/behind the inland moving sea breeze. Near term high-res runs over the past 8 hours have been pretty consistent in showing convection near the terminal. A PROB30 for TSRA was included 20-00z to account for this isolated activity.

Extended Aviation Outlook: No high confidence concerns.

MARINE

Through Tonight: A cold front will cross the waters today, likely becoming stationary just to the south. Northeast winds with a bit of post frontal surge will veer more easterly this afternoon as the sea breeze develops and moves inland. A lighter southerly flow will return tonight. Seas will average 1-3 ft through the period, highest over the South Carolina offshore legs.

Thursday through Monday: Mostly favorable marine conditions are expected through the weekend as Atlantic high pressure extends westward across the area and into the Gulf. Expect an increase in winds along the coast during the afternoon and evening periods associated with the daily sea breeze circulation. Friday night into Saturday night the pressure gradient will tighten as an area of low pressure passes north of the area. Winds could gust 20-25 kt across the Charleston County waters. Otherwise, no marine hazards are anticipated through the forecast period.

CLIMATE

Record High Temperatures:

June 28: KCHS: 99/1998 KCXM: 100/1959 KSAV: 100/1998

Record High Minimum Temperatures:

June 27: KCHS: 77/2015 KSAV: 79/1952

June 28: KCHS: 78/2013 KCXM: 81/1998 KSAV: 80/1880

June 29: KCHS: 79/1977 KCXM: 83/1998 KSAV: 80/1885

CHS WATCHES/WARNINGS/ADVISORIES

GA...None. SC...None. MARINE...None.