textproduct: Charleston

SYNOPSIS

Weak high pressure will extend across the area into early next week.

NEAR TERM /UNTIL 6 AM FRIDAY MORNING/

The region will remain placed between high pressure aloft over the Gulf of America and a longwave trough extending southward from the Great Lakes region. A shortwave trough will ripple across the southern periphery of this longwave trough across the southeastern states today. This shortwave trough will provide some synoptic forcing to aid in convection this afternoon.

This Afternoon: An interesting set up today as thunderstorms this morning across the Charleston Tri-County produced thick cloud cover that is struggling to erode. Thus, there is a temperature gradient across the forecast area as of 2 PM, with upper 70s to around 80 across the Charleston Tri-County and Colleton County in SC, and mid to upper 80s elsewhere. Given the lack of daytime heating, precipitation chances have diminished across the area with thick, lingering cloud cover. Elsewhere, the forecast has changed very little, with showers and thunderstorms possible. The airmass remains very moist and unstable with SPC Mesoanalysis showing PWATs 2.0-2.1 inches and upwards of 2500 J/kg of ML CAPE. While CAPE values will be supportive of convection, SPC Mesoanalysis shows little to no shear to speak of. Therefore the severe risk remains marginal this afternoon. Damaging wind gusts will be the main hazard with any strong to severe storm that is able to form. Hail is also possible, given a freezing level slightly lower than previous days. Heavy rainfall is also possible this afternoon, with the HREF showing a >50% probability of greater than an inch of rainfall across most of the local area.

Overnight: Convection will gradually wind down through the night, although a risk for at least isolated showers/tstms will linger, especially at the coast. Lows will range from the lower 70s well inland to the upper 70s/near 80 at the beaches.

SHORT TERM /6 AM FRIDAY MORNING THROUGH SUNDAY/

Aloft, mid-lvl vort energy associated with an h5 shortwave will slowly traverse the Carolinas this weekend, the bulk of which interacts with a moderately unstable environment locally on Friday, before shifting offshore and/or departing to the north this weekend. Although shear is rather weak on Friday (0-6 km Bulk Shear between 15-20 kt), it should remain sufficient for maintaining thunderstorm clusters within a moist and moderately unstable environment marked by PWATs around 2 inches, SBCAPE around 1500-2000 J/kg, mid-lvl lapse rates between -7.5 to -8.5 C/km and modest DCAPE, suggesting the potential for a few stronger thunderstorms and/or perhaps a marginally severe thunderstorm Friday afternoon/evening. By Saturday, shear and mid-lvl forcing become weaker, suggesting slightly less precip coverage and more "general" type thunderstorms during peak diurnal heating hours as the pattern becomes more typical of summertime. However, a stronger thunderstorm can not be ruled out with ample moisture and heating in place, perhaps near an inland moving sea breeze. Afternoon highs should remain in the low- mid 90s, while overnight lows are mild, only dipping into the low- mid 70s inland to upper 70s/around 80 near the beaches and across Downtown Charleston.

On Sunday, convective activity resembles a summertime pattern with scattered afternoon/evening showers and thunderstorms that mostly remain sub-severe, but with a limited potential to become strong. The main issue will be warmer temps as the large-scale ridging expands across the Southeast United States. Afternoon highs should approach the mid 90s away from the beaches, and when combined with sfc dewpts in the low-mid 70s, support heat index values around 105 degrees. A downslope wind should help mix out dewpts sufficiently to keep heat index values just below Heat Advisory levels, but a few spots could touch 108 degrees during peak heating hours.

LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/

Ridging will continue to build over the Deep South early next week, while an upper level low could develop across the Caribbean and move toward the Southeast Coast by the middle of next week. Typical diurnal convection will continue Monday with scattered showers and thunderstorms forecast, before an increase in precip coverage is possible by the middle of next week as the mid-upper lvl disturbance arrives. Monday will display above normal temps with highs largely in the mid-upper 90s. These temps along with sfc dewpts in the mid 70s could support marginal Heat Advisory conditions during peak heating hours Monday afternoon. Thereafter, precip coverage could play a role in maintaining heat index values below Heat Advisory conditions mid week.

AVIATION /00Z FRIDAY THROUGH TUESDAY/

KCHS/KJZI/KSAV: The bulk of the thunderstorm activity has moved offshore as of 00Z, with lingering stratiform rain impacting all three terminals through the next few hours. Instability remains plentiful across southeastern GA so TSRA has been maintained at KSAV through 02Z, with -RA at KCHS and KJZI. Rainfall will taper off after 02Z with prevailing VFR prevailing through the remainder of the 00Z TAF period. Afternoon showers and thunderstorms will be possible again tomorrow, however the timing of any impacts is uncertain and confidence is low. Therefore only VCTS has been included near the end of the 00Z TAF period.

Extended Aviation Outlook: Periods of flight restrictions are likely at CHS/JZI/SAV terminals Friday afternoon/evening due to shower and thunderstorm activity. Precip coverage becomes more typical of a summertime pattern late weekend and into early next week, with TEMPO flight restrictions possible due to shower/thunderstorm activity each day at all terminals.

MARINE

Through Tonight: A S to SW flow will prevail through tonight as surface high pressure holds strong offshore. Winds will generally remain 15 kt or less, but some gusts to 20 kt are possible near the land/sea interface and Charleston Harbor this afternoon as the sea breeze moves inland. Seas will average 2-3 ft. Clusters of strong to severe tstms may move offshore this evening and pose a risk for wind gusts in excess of 34 kt, frequent cloud- to- ground lightning and vsbys less than 1 NM in locally heavy rainfall. Special Marine Warnings may be needed.

Friday through Tuesday: Weak mid-lvl energy departing the region early weekend could result in scattered shower/thunderstorm activity across local waters, and perhaps a strong and/or isolated severe thunderstorm. Outside convection, a typical summertime pattern will return late weekend and persist into early next week with Atlantic high pressure centered offshore and weak sfc troughing developing inland each day. This should result in relatively benign conditions across local waters, with south to southwest winds around 15 kt or less each day and seas between 2-4 ft early weekend, subsiding to 1- 3 ft heading into next week. A few gusts up to 20 kt are possible, highest along the coast and in the Charleston Harbor due to sea breeze influences each afternoon.

CHS WATCHES/WARNINGS/ADVISORIES

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