textproduct: Charleston

WHAT HAS CHANGED

All sections have been updated.

KEY MESSAGES

- 1) Periods of showers and thunderstorms this week through the weekend could bring locally heavy rainfall. The threat for organized severe weather is low at this time.

DISCUSSION

KEY MESSAGE 1: Periods of showers and thunderstorms this week through the weekend could bring locally heavy rainfall. The threat for organized severe weather is low at this time.

Satellite water vapor indicates that a some drier air is starting to push onshore along the coast of GA/SC. Near-term guidance indicates that H5 heights associated with a 593 dm ridge centered over the western Atlantic will build over the coastal counties. In fact, recent runs of the HRRR forecast soundings indicate a significant subsidence inversion centered around H7 near the coast. Further inland, PW values should remain a bit greater, generally between 1.8- 1.9". In addition, the H7 inversion appears a degree or two weaker than near the coast. Once the sea breeze develops and pushes inland, showers and thunderstorms should develop across inland GA and SC. Some of these storms may develop heavy downpours, however, potential for excessive rainfall appears less than the past several days. Given a bit less coverage of convection, temperatures may range a degree or two warmer than recent days. High temperatures are forecast to range around 90 along the coast to the upper 80s inland. In the wake of the sea breeze, deeper mixing may yield a period of gusts between 20-25 mph this afternoon.

As an upper level trough begins to move out of the northeast on Wednesday, the ridge of high pressure off to our east starts to move off to the south. While that occurs throughout the day, the surface high pressure similarly shifts southwards. Before it moves too far away, the continuation of similar meteorological conditions will result in warm and moist conditions, with chances for showers and thunderstorms continuing. The most widespread coverage is expected during the afternoon and evening hours after the sea breeze initiated the thunderstorms, and given PWATs remaining near 2 inches, locally heavy rainfall will remain possible. Temperatures remain warm, in the mid 80s to lower 90s.

Moving into Thursday, the aforementioned upper level trough has an accompanied surface cold front that moves towards the area from the north. The front will bring additional chances for showers and thunderstorms, mostly starting in the afternoon, with temperatures remaining warmer in the upper 80s to lower/mid.

Rain chances will increase Friday and into the weekend as the front meanders/stalls in the vicinity, bringing a more widespread pattern of showers and thunderstorms. Models continue to hint that a weak surface low pressure (or two) may spawn along the front, though ensemble clustering analysis shows rather poor agreement, lowering confidence a smidge. Moisture convergence along the front and/or surface lows will increase PWATS to around 2.0 - 2.2 inches Friday and into the weekend. Several rounds of rainfall which could be heavy at times, may lead to localized minor flooding, especially in areas that see repeated storms. Current forecast guidance suggests widespread rainfall totals through the weekend remain around 2 to 4 inches. The NBM continues to show a 20-35% probability of 3 inches of rain or greater falling over a 72-hour period between Friday and Monday morning, with the highest chances located along the coast. While confidence is increasing in a wetter pattern later this week and weekend, details on exact rainfall totals and where the heaviest rain sets up will likely change over the coming days.

AVIATION /12Z TUESDAY THROUGH SATURDAY/

Prior to the 12Z TAFs, KCLX detected some patches of showers near KSAV. The terminals will remain under slightly stronger mid-level ridging today. Convection should favor areas west of I-95. KSAV will see the greatest chance for showers around dawn and again late this morning with the onset of the sea breeze, highlighted with VCSH this morning with a TEMPO from 20-23Z. Once the sea breeze passes, south winds should strengthen to 10 to 15kts with gusts into the low 20 kts. South winds are forecast to settle near 10 kts by 23Z.

Extended Aviation Outlook: TEMPO flight restrictions possible with showers and thunderstorms at CHS/JZI/SAV terminals during the afternoon hours into the later half of the week. In addition, patchy overnight fog and/or stratus cannot be ruled out after recent rains.

MARINE

Today and tonight: The marine zones will remain under the influence of broad high pressure through the period. South winds should remain between 10 to 15 kts with some gusts into the low 20s. Wave heights will favor values between 4-5 ft.

Wednesday through Saturday: Conditions are forecast to remain below Small Craft Advisory criteria into the beginning of the weekend, with daily chances for showers and thunderstorms. Thursday and Friday will see a stalled front near the area, keeping winds on the weaker side. There is potential for a weak surface low pressure (or two) to form along the stalled front, which would bring an increase in wind speeds along with wave heights to near/above Small Craft Criteria on Sat/Sun, with confidence low/moderate at this time.

Rip Currents: An elevated rip current risk will remain through the week with a modest easterly swell around 3 to 4 feet every 7 seconds and sea breeze influences. A moderate risk of rip currents is in place for all area beaches through at least Wednesday.

CHS WATCHES/WARNINGS/ADVISORIES

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