textproduct: Charleston

WHAT HAS CHANGED

All sections have been updated.

KEY MESSAGES

- 1) Locally heavy rainfall is possible today as a stalled front remains in the vicinity of the South Carolina Lowcountry.

- 2) Hot and humid conditions return to the South Carolina Lowcountry and Southeast Georgia during the middle of this week.

DISCUSSION

KEY MESSAGE 1: Locally heavy rainfall is possible today as a stalled front remains in the vicinity of the South Carolina Lowcountry. At the surface, a stalled front remains draped across portions of the South Carolina Lowcountry today, oriented from the Charleston county coastline through Summerville and up towards Columbia, SC. Aloft, a h500 trough continues to slowly deepen along the east coast as weak shortwaves move through the northwesterly flow. Moisture remains plentiful across the southeast region, with PWATs remaining above 2.0" through today while pockets of values to near 2.5" are expected. The 12Z CHS observed sounding showed a long and skinny CAPE profile with a PWAT of 2.17", just above the 90th percentile of climatology for the date, with MLCAPE of near 1900 J/kg. Forecast soundings continue to show long and skinny profiles throughout the day, with peak MLCAPE values of 2000-3000 J/kg by early this afternoon.

Throughout the rest of the afternoon hours, expect the ongoing convection across the Charleston quad-county region to continue developing along the aforementioned front, further aided by the shortwaves aloft and an expected afternoon sea-breeze. As a result, locally heavy rainfall will remain possible this afternoon into the evening, as is currently observed across the Mount Pleasant, SC region. Guidance continues to hint that a weak low pressure may form along the front, which would further increase the convergence of moisture, further increasing the heavy rainfall threat. While the latest 12Z HREF rainfall accumulation probabilities have decreased slightly, with 50-70% chances for 1"/3hr and 10-30% for 3"/3hrs, the longer duration of rainfall chances today will keep flooding chances elevated this afternoon, especially for the Charleston quad-county. Compared to what has been observed this afternoon with some spots in Mount Pleasant approaching 4 inches, the HREF probabilities seem to be running a touch on the lower side. The Flash Flood Watch for the Charleston quad-county region will continue into the evening hours, current expected to expire at 10 PM.

In addition to the heavy rainfall threat, steep low-level lapse rates with the high PWATs may enhance downdraft strength, bringing a risk for strong damaging wind gusts of 50 to 60 mph. While the risk for locally heavy rainfall can't be ruled out moving south into southeast Georgia, the current thinking is that the fronts position will remain south of the I-26 corridor but north of the SC/GA state line, which will keep the risk with the risk for locally heavy rainfall along and north of the front.

KEY MESSAGE 2: Hot and humid conditions return to the South Carolina Lowcountry and Southeast Georgia in the middle of this week.

A strong mid-lvl ridge will continue to situate itself over the Rockies and the Plains through the mid-week, while a troughing will be apparent along the Eastern Seaboard. At the surface, weak high pressure will also prevail through the mid-week. This will yield hot and humid conditions throughout the week, with Tuesday and Wednesday being the hottest days of the week. Expect daytime highs to reach into the mid to upper 90s. There is a chance that some spots could reach the 100 degree mark across far inland Georgia. Dewpoints are expected to be in the low 70s far inland, and then increasing into the mid to upper 70s at the coastline with the afternoon sea breeze. This will equate to afternoon heat indices ranging from 100-105F inland, and 108-114F across the coastal counties on Tuesday and Wednesday. If this forecast trend continues, we'll likely need to issue a heat headlines for both days. Thereafter, the heat and humidity will drop near normal values on Thursday with the arrival of another front.

AVIATION /18Z SUNDAY THROUGH FRIDAY/

18Z TAFs - Scattered to numerous showers and thunderstorms have developed across the Charleston tri-county area, with additional development expected throughout the afternoon hours for the area. This will continuing chances for brief MVFR-IFR cigs and visbys during thunderstorm activity. Further south into southeast Georgia, convection will likely be more isolated. Convection coverage decreases throughout the evening into the overnight hours. Winds will remain variable throughout the period as a weak front lingers and meanders around.

Extended Aviation Outlook: Brief flight restrictions are possible Wednesday and Thursday due to showers and thunderstorms.

MARINE

Through tonight: A quasi-stationary front will linger nearby as light southwesterly flow persists across the local waters. This set- up will likely yield isolated to scattered showers and thunderstorms into the afternoon/evening hours. As southeasterly swell continues to surge into the local waters, expect seas to range from from 2 to 3 ft.

Monday though Friday: Light to moderate winds should continue across the local waters on Monday, before a cold front approaches from the region. As this front inches closer, expect wind speeds to increase on Tuesday afternoon with gusts reaching up to 25-27 kts. Therefore, Small Craft Advisories will likely be needed for a portion of the waters on Tuesday and Wednesday. Thereafter, marine conditions will remain rather benign on Thursday and Friday. Seas will range from 2- 3 ft through most of period, except for briefly surging to 3-5 ft (possible 6 footers in the offshore waters) on Tuesday evening through Thursday morning.

CLIMATE

Record High Temperatures:

July 28: KCHS: 101/1949 KCXM: 100/1936 KSAV: 102/1949

July 29: KCHS: 100/1993 KCXM: 99/1999 KSAV: 103/1993

Record High Minimum Temperatures:

July 29: KCHS: 80/2016 KCXM: 85/1999 KSAV: 82/1878

CHS WATCHES/WARNINGS/ADVISORIES

GA...None. SC...Flood Watch until 10 PM EDT this evening for SCZ043>045-149- 150-152. MARINE...None.