textproduct: Charleston

WHAT HAS CHANGED

All Key Messages and sections were updated.

KEY MESSAGES

- 1) Breezy conditions with summer-like temperatures today across the South Carolina Lowcountry and Southeast Georgia. Record low maximum records will be challenged this morning.

- 2) Above-normal temperatures and below-normal rain chances are expected through the upcoming weekend. Temperatures could approach the triple digits this weekend.

DISCUSSION

KEY MESSAGE 1: Breezy conditions with summer-like temperatures today across the South Carolina Lowcountry and Southeast Georgia. Record low maximum records will be challenged this morning.

This Morning: Regional VAD wind profiles show a modest low- level jet (LLJ) is strengthening across the area early this morning as the region remains pinned between high pressure centered well offshore and an approaching cold front. Near term guidance shows the intensity of the LLJ peaking near to just after daybreak which will help keep the atmosphere very well mixed through the diurnal minimum as the low-level wind field starts to increase. Low temperatures are on track to bottom out in the mid 70s west of the I-95 corridor with upper 70s/lower 80s east of there to the beaches including Downtown Charleston. The record high minimums at all three climate sites will be challenged. See the climate section below for more details. Patchy upstream convection over western Georgia should dissipate prior to reaching this far to the east.

Today and Tonight: Breezy west winds (15-25 mph with gusts to 30 mph) and hot conditions will prevail as the combination of increasing low-level warm air advection, a modest westerly flow aloft and broad subsidence ahead of an approaching cold front help to push highs in the lower-mid 90s for many locales this afternoon. The westerly flow aloft will help pin the sea breeze along or even just offshore of the beaches through the day. This should allow very warm temperatures to reach all the way to the beaches with upper 80s/lower 90s possible. A blend of the various high resolution data sets also suggests a pocket of mid 90s could even infiltrate much of the Charleston peninsula-- something that is not observed but just a few times a year with the sea breeze holding to the east. The record highs at the climate sites are in the 100-102 range and look safe. The westerly flow and building subsidence/mid-level drying aloft will help mix out dewpoints into the upper 60/lower 70s during peak heating, but some mid 70s are likely to linger across parts of Long, McIntosh and coastal Liberty Counties before the impacts of drying aloft reach that far south. So, while heat indices are poised to peak in the mid-upper 90s inland with 98-102 across much of the coastal corridor, values as high as 105-107 could occur for a few hours in areas such as Darien, Townsend, Eulonia, Halfmoon Landing and Shellman Bluff. While some isolated spots could reach as high 108-109 at times, the situation just looks too marginal for a Heat Advisory at this time.

The prospects for diurnal convection developing this afternoon is poor. Drying mid-levels and subsidence aloft ahead of the cold front will keep the atmosphere fairly well capped. The only exception is over the counties bordering the Altamaha River where the impacts of mid-level drying will not arrive until later in the afternoon/early evening. Forecast soundings at KJES and KLHW suggest the cap will mix out by mid-afternoon, but just barely. 20-30% pops were highlighted across the far south closer to the Altamaha River with pops <10% elsewhere. Any convection that is able to develop will quickly dissipate just after sunset with rain-free conditions prevailing overnight.

Lake Winds: Deep mixing will support winds 15-20 kt with frequent gusts to 25 kt over Lake Moultrie today with waves 1-2 ft. A Lake Wind Advisory is in effect from 8 AM until 5 PM.

KEY MESSAGE 2: Above-normal temperatures and below-normal rain chances are expected through the upcoming weekend. Temperatures could approach the triple digits this weekend.

A weak cold front will push offshore Wednesday as Atlantic high pressure extends westward across the forecast area. Aloft, broad troughing will transition to a building ridge and increasing subsidence, limiting convection through the weekend. Additionally, relatively dry low and mid-level air will persist through most of the week, further suppressing convection, with no more than isolated shower or thunderstorm activity expected.

Despite near-normal temperatures forecast Wednesday with the recent passage of a weak cold front, a gradual warming trend is forecast through the remainder of the week and into the weekend. High temperatures are expected to reach the mid to upper 90s Friday, with upper 90s becoming common across much of the area Saturday and Sunday. A few locations could even exceed 100 degrees this weekend. Combined with dew points in the 70s, heat index values could reach 108-112F, especially across the coastal counties. Additionally, being that convection is forecast to be isolated, we do not expect much relief from showers. While confidence in the magnitude of the heat 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.

AVIATION /06Z TUESDAY THROUGH SATURDAY/

23/06z TAF Discussion: KCHS/KJZI/KSAV: VFR through the entire TAF period. Westerly winds will increase closer to daybreak and become gusty. Gusts should peak in the 24-28 kt range from mid-morning through late afternoon. Conditions could get close to low-level wind shear (LLWS) criteria through about 10z as the low-level jet intensifies. The situation looks a bit marginal, so any mention of LLWS was withheld at this time. If winds on regional radar VAD wind profiles increase more than expected, then amendments to include LLWS may be issued.

Extended Aviation Outlook: No high confidence concerns.

MARINE

Through Tonight: A modest nocturnal surge is ongoing across the waters early this morning with the highest winds (15-20 kt with frequent gusts 25-28 kt) being observed off the Charleston County coast. Winds will holding steady if not increase a tad more through daybreak as the low-level jet peaks. Winds may diminish some this morning, but will then pick back up this afternoon reaching 20-25 kt with gusts to 30 kt over the South Santee-Edisto Beach nearshore and offshore legs with 15-20 kt with gusts to 25 kt across Charleston Harbor and the Edisto Beach-Savannah nearshore and offshore legs. Small Craft Advisories are posted for these areas. Winds over the Savannah- Altamaha River nearshore and offshore legs look to remain below frequent 25 kt gusts, but it may be close for the northern portions of the offshore leg. Winds will begin to diminish late this afternoon and diminish further overnight as the low-level jet propagates east and a weak cold front drop south through the waters. Seas 2-4 ft nearshore, 3-5 ft offshore will build to 3-5 ft, except 4-6 ft over the South Santee-Edisto Beach nearshore and offshore legs late this afternoon/evening before diminishing overnight.

Wednesday through Sunday: Favorable marine conditions are expected across the local waters through the weekend. A weak front located offshore Wednesday will dissipate by Thursday as Atlantic high pressure extends westward over the region. Expect an increase in winds along the coast during the afternoon and evening periods associated with the daily sea breeze circulation. Otherwise, no marine hazards are anticipated through the forecast period.

Rip Currents: Breezy southwest winds along the Charleston County beaches will support a moderate risk for rip currents through this evening. Conditions look to remain in the low risk category for all remaining beaches.

CLIMATE

Record High Temperatures:

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

Record High Minimum Temperatures:

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

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

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

CHS WATCHES/WARNINGS/ADVISORIES

GA...None. SC...Lake Wind Advisory from 8 AM this morning to 5 PM EDT this afternoon for SCZ045. MARINE...Small Craft Advisory from 8 AM this morning to 5 PM EDT this afternoon for AMZ340-362. Small Craft Advisory until 8 PM EDT this evening for AMZ360.