textproduct: Charleston

WHAT HAS CHANGED

All sections have been updated.

KEY MESSAGES

- 1) Smoke from the Horse Island Wildfire will impact northeast Berkeley County tonight into Tuesday.

- 2) Hot and humid conditions across coastal South Carolina and Georgia through mid-week. Heat Advisories could be needed.

- 3) A slow-moving cold front may bring greater rainfall chances late this week through this weekend.

DISCUSSION

KEY MESSAGE 1: Smoke from the Horse Island Wildfire will impact northeast Berkeley County tonight into Tuesday.

A Dense Smoke Advisory has been requested by the U.S. Forest Service for northeast portions of Berkeley County in response to the Horse Island Wildfire. Smoke in the vicinity of the fire is significant and conditions will deteriorate overnight as the nocturnal inversion develops. The latest Hysplit output shows the worst of the smoke will remain across northeast Berkeley County and extend across the Santee River into a small area of southwest Georgetown County. Visibilities may drop below 1 mile at times overnight, especially along parts of Highway 45. Road closures are possible. Smoke will likely remain an issue into Tuesday although visibilities should improve some by mid-morning as dispersion increases and mixing heights rise. Another Dense Smoke Advisory may be needed Tuesday night as smoke settles during the overnight hours.

KEY MESSAGE 2: Hot and humid conditions across coastal South Carolina and Georgia through mid-week. Heat Advisories could be needed. The forecast area will remain of the edge of a H5 ridge centered off the Southeast U.S. coast. Sfc high pressure over the western Atlantic will provide the region with south winds Tuesday and Wednesday, with occasional gusts during the afternoon. This pattern should support hot daytime temperatures, with highs generally in the mid 90s. Afternoon dewpoints may range in the mid to upper 70s, especially after the passage of the sea breeze. Heat index values may peak between 105 to 109 degrees right along the coast. It is possible that a Heat Advisory could be needed.

Low temperatures are forecast to range in the upper 70s, with values around 80 degrees along the coast. The mild low temperatures could challenge some record high low temperatures this week, see Climate Section below.

KEY MESSAGE 3: A slow-moving cold front may bring greater rainfall chances late this week through this weekend.

Recent runs of the GFS and ECMWF indicate that a cold front may reach the forecast area by early Thursday. Guidance indicates that the front will slow as it approaches the coast, then possibly remain nearly stationary through this weekend. At H5, a broad trough is forecast to settle over the east coast, possibly amplifying into Sunday. Forecast soundings indicate very moist conditions across the region, with PW values possibly ranging between 2.2 to 2.4 inches on Saturday. Given the deep moisture, synoptic scale forcing, and periods of moderate instability, the forecast will feature at least likely PoPs. The Excessive Rainfall Outlooks Wednesday through Friday indicates a Marginal Risk for the area.

AVIATION /00Z TUESDAY THROUGH SATURDAY/

21/00z Aviation Discussion: KCHS/KJZI/KSAV: VFR through 22/00z.

Extended Aviation Outlook: Prevailing VFR through mid- week. Chances of flight restrictions increase later this week with a greater coverage of showers/thunderstorms.

MARINE

Today and tonight: The gradient will remain pinched between high pressure centered offshore and an inland trough. South to southwest winds could gust up to 20 kt, but should remain below Small Craft Advisory criteria. With little to no swell energy, seas will range from 2 to 3 ft through the evening, before increasing to 3 to 4 ft overnight.

Tuesday through Friday: The pressure gradient will tighten across the coastal waters as a cold front approaches from the north and a east-west sfc ridge remains to the south. This pattern should support increasing south winds on Tuesday, with gusty conditions expected across the marine zones into Wednesday night. In addition, seas will build on Tuesday, with 6 ft sea common across the waters Tuesday night in Wednesday morning. A Small Craft Advisory is in effect from Tuesday afternoon to Wednesday night. As a cold front approaches the region on Thursday and remains into Friday, the pressure gradient across the region will weaken. Thursday and Friday, winds are forecast to remain from the south between 15 to 20 kts with seas around 3 ft.

Rip Currents: A Moderate Risk of rip currents is in effect for the SC and GA beaches through Wednesday, given enhanced winds along the coastline and wave periods up to 6 seconds. Breakers may exceed 4 ft on Wednesday, with wave periods between 6 to 7 seconds. It is possible that a portion of the SC coast may need a high risk if swell waves or wind speeds increase from the current forecast.

CLIMATE

Record High Minimum Temperatures:

July 20: KCHS: 79/2025 KCXM: 83/2000 KSAV: 79/1942

July 21: KCHS: 80/1986 KCXM: 83/1998

July 22: KCHS: 81/2011 KCXM: 83/2011

CHS WATCHES/WARNINGS/ADVISORIES

GA...None. SC...Dense Smoke Advisory until 10 AM EDT Tuesday for SCZ045. MARINE...Small Craft Advisory from noon Tuesday to 5 AM EDT Thursday for AMZ360-362. Small Craft Advisory from 2 PM Tuesday to midnight EDT Wednesday night for AMZ364-384.