textproduct: Charleston

WHAT HAS CHANGED

The Aviation section has been updated for the 00z TAF issuance. Added a Key Message for coastal flooding potential mid to late week.

KEY MESSAGES

- 1) Rain chances increase on Tuesday.

- 2) A cold front could bring a threat of strong thunderstorms Wednesday afternoon, and will be followed by cooler weather and gusty winds.

- 3) The threat for coastal flooding will increase mid to late week.

DISCUSSION

KEY MESSAGE 1: Rain chances increase on Tuesday.

Through Tonight: Little change in the overall pattern has occurred during the past 24 hours in regards to an upper low meandering over Florida and deep moisture advecting across the local area with PWATs near 2 inches. Shower activity could linger into early evening hours, but should dissipate within a few hours of sunset. Locations that see rainfall today will be more at risk for patchy to areas of fog late tonight, especially inland for a few hours prior to and around daybreak.

Tuesday: The aforementioned upper low across Florida will begin to drift north across the Southeast United States, likely to bring higher chances of showers/thunderstorms locally despite trending weaker well in advance of a longwave trough making way across the Midwest. The uptick in forcing along with modest instability and residing 2+ inch PWATs could support a few stronger thunderstorms during mid-late afternoon into early evening hours, perhaps with some enhancement along/near a seabreeze. Localized heavy rainfall and minor flooding issues are also possible. However, the overall severe weather threat should be on the lower end.

KEY MESSAGE 2: A cold front could bring a threat of strong thunderstorms Wednesday afternoon, and will be followed by cooler weather and gusty winds.

The previously mentioned upper low is anticipated to shift north- northeast of the local area, becoming phased with a longwave trough shifting across the Mid-Atlantic and Northeast States mid-week. A notable cold front is progged to push south into the local as the mid-upper lvl pattern supports digging of the longwave trough across the Southeast. Timing of fropa will remain key in regards to the overall threat for stronger and/or marginally severe thunderstorms Wednesday. Although latest trends suggest cold fropa beginning late Tuesday night into Wednesday morning, there could be sufficient time for strong sfc heating to occur within a deeply moist environment across Southeast Georgia Wednesday afternoon, leading to a greater risk for stronger and/or marginally severe thunderstorms prior to sunset.

Following the front, an inland wedge will set up across the Carolinas and Georgia, favoring cool and drier conditions locally within a north-northeast flow during the second half of the week. Cold air advection and a tightening pressure gradient should lead to breezy conditions post fropa Wednesday and Thursday, with some enhancement possible near coastal areas. In general, highs temps in the mid-upper 70s to lower 80s for Southeast SC and low/mid 80s for Southeast GA are most probable into late week.

KEY MESSAGE 3: The threat for coastal flooding will increase mid to late week.

As a full moon approaches on 9/26, breezy northeast winds Wednesday evening into Friday may result in some coastal flooding issues as tidal departures rise. We will need to keep an eye on the potential starting as early as Wednesday afternoon for coastal Charleston and Colleton counties, expanding southwards to include the remainder of the SE SC coast into SE GA Thursday afternoon/evening.

AVIATION /00Z TUESDAY THROUGH SATURDAY/

VFR is expected to prevail through at least the first half of the night. Thereafter, guidance hints that another round of stratus and fog will be possible. The greater chance for occurrence is at KSAV where MVFR has been maintained, though there is potential for IFR or lower. VFR should return mid morning. Brief restrictions in showers/thunderstorms will be possible in the afternoon, which is currently highlighted with PROB30 groups.

Extended Aviation Outlook: Flight restriction chances increase Tuesday into Wednesday at all terminals with a showers and thunderstorms and a building wedge post fropa Tuesday night into Wednesday. Gusty north-northeast winds are likely to follow at all terminals Wednesday into Thursday as well.

MARINE

Through Tuesday: A decaying surface high pressure ahead of a slowly approaching cold front will continue the benign marine weather conditions across our local waters. Periodic showers and thunderstorms during this time may be capable of gusty winds and frequent lightning.

Wednesday-Friday: A cold front will be pushing through on Wednesday, with a strong surge in northeasterly flow as the pinched pressure gradient (aka the wedge) sets up. Breezy ramp up during the evening hours, with wind gusts in excess of 25 knots have 60-90% chances, so Small Craft Advisories are anticipated. There is also a low chance (20-30%) for Gales to develop on Thursday, for the zones 20+nm offshore. In addition, wave heights of 5-7 ft will likely accompany the breezy winds for areas 15+ nm away from the coast Thursday morning through Friday evening before winds begin to weaken.

Saturday: The wedge continues to weaken, further decreasing the wind strength throughout the day. Seas will remain unsettled, with offshore zones (20+nm offshore) seeing 6ft+ waves continuing into the evening hours before decreasing below 6 ft.

CHS WATCHES/WARNINGS/ADVISORIES

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