textproduct: Charleston

WHAT HAS CHANGED

All sections and Key Messages have been updated.

KEY MESSAGES

- 1) A fairly typical summertime pattern is forecast with daily shower and thunderstorm chances through the weekend.

DISCUSSION

KEY MESSAGE 1: A fairly typical summertime pattern is forecast with daily shower and thunderstorm chances through the weekend.

Through tonight, the synoptic pattern has changed little since Sunday with the region will positioned along the western flanks of Atlantic high pressure centered well offshore. The flow aloft will be bit more westerly compared to 24 hours ago which will tend to keep the sea breeze pinned to the immediate coast for much of the day with it possibly beginning a extremely slow inland trek closer to late afternoon, especially along the lower South Carolina coast. Warm and moist conditions will remain place today with dewpoints likely to hold in the lower-mid 70s except over parts of the Charleston Tri-County into Colleton County where the moisture depth is a bit more shallow and more vigorous vertical mixing could allow dewpoints to mix out in the upper 60s in spots. Highs are poised to warm into the lower- mid 90s for many spots with heat indices peaking in the 100-106F range which is below the local Heat Advisory criteria of 108F. Similar to yesterday, the airmass will remain supportive of pulse convection in the absence of any meaningful synoptic forcing mechanisms. The convective pattern will likely be augmented on the mesoscale at times with an isolated strong or severe tstm becoming possible where updrafts can be locally enhanced by boundary collisions near the sea breeze or other convective outflows. Wind gusts 40-60 mph, frequent cloud-to- ground lightning and locally heavy rainfall will be the primary hazards. Pops 20-30% look reasonable for most areas this afternoon with convection winding down during the evening hours. Will have to watch for some nocturnal convection approaching interior Southeast Georgia from the west closer to the midnight, but most of this should dissipate prior to reaching this far east as diurnal instability wanes.

A southwesterly flow ahead of approaching cold front will likely keep the boundary well mixed for many areas overnight. This will tend to keep temperatures up through sunrise with lows likely only bottoming out in the lower-mid 70s west of I-95 with upper 70s/near 80 elsewhere. The record high minimums at all three climate sites could be challenged, assuming convection during the day Tuesday does not drive temperatures below record levels prior to 1 AM Wednesday. See the climate section below for additional details.

Guidance suggests a weak cold front will move toward the Carolina coast and across central Georgia Tuesday and then stall, remaining nearly through the end of the week. Isolated to scattered showers and thunderstorms are possible Tuesday, owing to the front in the vicinity. but deep westerly flow advecting drier air into the area will limit convection. Then a seasonable combination of offshore ridging/inland troughing reestablishes through the day Wednesday and persists into the weekend, with weak subsidence aloft maintaining mainly isolated to scattered diurnal daily convection. A few stronger storms are possible each afternoon, but there is no apparent significant severe threat at this time.

AVIATION /06Z MONDAY THROUGH FRIDAY/

22/06z TAF Discussion: KCHS/KJZI/KSAV: VFR for much of the period. An area of expanding MVFR cigs over interior Southeast Georgia could make a run for mainly KCHS and KSAV prior to daybreak. TEMPO groups for MVFR cigs were introduced 09-12z at those terminals for now. Amendments may be needed if the risk for prevailing MVFR cigs become more apparent. Isolated shower/tstms are expected this afternoon. Impact probabilities are too low to justify a mention of TSRA at any of the terminals at this time. The need to mention TSRA will be reevaluated for the 12z TAF cycle.

Extended Aviation Outlook: Brief flight restrictions are possible with mainly afternoon showers and thunderstorms.

MARINE

Today: A broad southerly flow regime will persist across the waters today as high pressure holds well offshore. A westerly flow aloft will delay the development of the sea breeze, but one should eventually develop, but remained pinned to/near the coast until late. West winds 10-15 kt will back to the southwest later in the day, but increase to 15-20 kt with gusts to 25 kt across the South Santee-Edisto Beach nearshore and offshore legs later this afternoon. Seas will build to 2-4 ft.

Tonight: The pattern looks to favor a classic summer nocturnal surge tonight as high pressure remains well offshore and a cold front approaches from the northwest. The highest overnight winds look to center across the South Carolina nearshore and offshore waters with the risk for reaching frequent gusts 25-30 kt peaking over the South Santee-Edisto Beach nearshore and offshore legs. HREF probabilities for frequent gusts >25 kt surge as high as 30-65% by 4 PM this afternoon across these waters and peak 70-100% a few hours prior to daybreak Tuesday. Given these trends and the pattern setup, a Small Craft Advisory has been issued for the South Santee-Edisto Beach nearshore leg from 4 PM until 6 AM Tuesday. The advisory may need to be expanded south into the Edisto Beach-Savannah nearshore leg later today, but the situation looks a bit too marginal to hoist an advisory at this time. Although advisory thresholds will be met over both South Carolina offshore zones, Small Craft Advisories are not currently being issued for these waters. Seas will average 2-4 ft, except build to 4-5 ft over the South Santee-Edisto Beach offshore leg after midnight.

Tuesday through Saturday: A weak cold front will approach the Carolina Coast Tuesday and stall through the end of the week. A pinched pressure gradient from offshore high pressure and low pressure in the Mid Atlantic will result in gusts approaching 25 knots at times Tuesday, especially across the Charleston County nearshore waters. A brief Small Craft Advisory could be needed, mainly between the afternoon and evening hours. Thereafter, the pressure gradient will relax as high pressure gradually rebuilds over land. There are no additional marine concerns through the remainder of the period.

CLIMATE

Record High Minimum Temperatures:

June 23: KCHS: 78/2024 KCXM: 82/1998 KSAV: 77/2017

CHS WATCHES/WARNINGS/ADVISORIES

GA...None. SC...None. MARINE...Small Craft Advisory from 4 PM this afternoon to 6 AM EDT Tuesday for AMZ360.