textproduct: Charleston

WHAT HAS CHANGED

All sections have been updated.

KEY MESSAGES

- 1) Increased chances for showers and thunderstorms through the weekend, with isolated strong/severe storms possible across the interior late this afternoon into early evening.

DISCUSSION

KEY MESSAGE 1: Increased chances for showers and thunderstorms through the weekend, with isolated strong/severe storms possible across the interior late this afternoon into early evening.

Aloft, h5 vort energy will ripple across the Deep South and Southeast United States today along the western periphery of an Atlantic ridge, encountering a moist (PWATs ~1.75 to 2.0 inches) and increasingly warming environment this afternoon, which will result in a period of scattered to numerous showers along with embedded thunderstorms mid-late afternoon into early evening.

Latest mesoanalysis suggests a worked over atmosphere earlier this morning recovering with sunshine and a southerly flow this afternoon. Afternoon highs in the mid-upper 80s combined with sfc dewpts in the low-mid 70s support sufficient instability for afternoon convection with an axis of MLCAPE near 2000-2500 J/kg across Southeast Georgia where strongest sfc heating has taken place with breaks in cloud cover. Deep-layered shear remains somewhat modest (20-25 kt) today, suggesting unorganized shower/thunderstorm activity for most areas. However, shear is strongest well inland and coincides with highest instability, and when combined with forcing associated with h5 vort energy and an inland progressing sea breeze could support a few strong/severe storms within multicellular thunderstorm clusters mid afternoon into early evening (mainly along and west of the I-95 corridor in Southeast Georgia and Southeast South Carolina). Most activity should then weaken/erode as instability wanes due to the loss of daytime heating by mid evening. The latest 12Z HREF ensemble paintball does highlight a few spots of updraft helicity (>75 m2/s2) in the noted area above. Low-lvl lapse rates around 7-7.5 C/km and DCAPE near 500-750 J/kg also suggest mainly a damaging wind concern should a severe thunderstorm occur. The Storm Prediction Center continues to highlight the noted area in a Marginal Risk for severe weather today.

Another concern with convective activity mid afternoon into early evening is the potential for localized heavy rainfall/minor flooding. Hires guidance continues to suggest a corridor of heavy rainfall from Tattnall County, GA to Allendale County, SC, likely due to northerly storm motions running parallel to a sea breeze boundary, and therefore prolonging rainfall from multiple rounds of shower and thunderstorm activity over the noted area. The 12Z HREF highlights this area with 1-2 inches of rainfall accumulation with localized amounts of 2+ inches this afternoon through tonight. Although this will be considered a mostly beneficial rain event in an area experiencing Exceptional to Extreme Drought, rainfall rates could become locally excessive during thunderstorms late afternoon into early evening, and if so could lead to minor flooding issues. The Weather Prediction Center continues to highlight the noted area above in a Marginal Risk for excessive rainfall.

On Sunday, conditions are not expected to change much from today, with comparable temperatures and moisture content. The sea breeze will again be the focus the initial thunderstorms, then coverage should expand across inland areas. Locally heavy rainfall is possible generally along and west of I-95.

Next week, warm and moist conditions persist as the upper ridge shifts back towards the southeast United States, which should support a more summer-like pattern with diurnally driven convection each day, initially along a sea breeze before expanding across inland areas mid-late afternoon into evening hours. Temps will remain above normal, with daily highs in the upper 80s/lower 90s and overnight lows only in the mid 60s to mid 70s, possibly resulting in record high minimum temperatures.

AVIATION /18Z SATURDAY THROUGH THURSDAY/

VFR conditions should prevail at CHS/JZI/SAV early afternoon with a southeast wind gusting up to 10-15 kt behind a sea breeze shifting inland. Chances for showers and thunderstorms increase late afternoon to early evening timeframe, with the higher chances occurring at the SAV terminal where TEMPO -TSRA remains between 23Z Saturday to 03Z Sunday. PROB30 groups have been shortened at CHS/JZI early evening based on radar and model trends. VFR conditions should prevail for much of the night and into late morning hours Sunday. PROB30 groups have been introduced at all terminals between 16-18Z Sunday for isolated thunderstorms developing along a sea breeze.

Extended Aviation Outlook: TEMPO flight restrictions possible with showers and thunderstorms at CHS/JZI/SAV terminals during the afternoon hours Sunday into the middle of next week.

MARINE

This Afternoon and Tonight: Onshore flow will prevail along the western periphery of Atlantic high pressure, with some local enhancement to southeasterly winds (~15 kt) along the land/sea interface today, including the Charleston Harbor. Southerly winds in the 10-15 kt range are likely overnight. Seas will generally range between 3-4 ft, although could slightly build about a ft during the night.

Sunday through Thursday: Conditions are forecast to remain below Small Craft Advisory criteria through at least the middle of next week, with daily chances for showers and thunderstorms. High pressure to the east will drive onshore ESE flow each day, with wind speeds averaging in the 10-15 knot range. Each afternoon and evening there could be some local enhancement along the land/sea interface with the diurnal sea breeze. Seas will average 2-4 feet through the period.

Rip Currents: A modest easterly swell around 3ft/8s and sea breeze influences each afternoon will keep the rip current risk in the moderate category at all area beaches through Monday.

CHS WATCHES/WARNINGS/ADVISORIES

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