textproduct: Charleston

WHAT HAS CHANGED

The Aviation Section has been updated for the 12Z TAF issuance.

KEY MESSAGES

- 1) Coastal flooding and significant coastal hazards are expected during the middle of this week.

- 2) Cooler temperatures along with breezy conditions are expected during the middle of this week.

- 3) NHC has identified a disturbance in the southwestern Gulf with a high chance of tropical cyclone formation during the next 48 hours. Regardless of development, heavy rainfall could develop over the Southeast United States by this weekend.

DISCUSSION

KEY MESSAGE 1: Coastal flooding and significant coastal hazards are expected during the middle of this week.

Coastal Flooding: Strong northeast winds associated with a wedge of high pressure inland and low pressure offshore in combination with high astronomical tide levels will likely support coastal flooding issues during high tide cycles today through Thursday and possibly into Friday.

For Charleston and Coastal Colleton Counties, the greatest risk for coastal flooding is expected with late afternoon/early evening high tide cycles today and Wednesday with moderate saltwater inundation possible (~7.5 ft MLLW at Charleston Harbor, SC). Additionally, minor coastal flooding is possible during morning high tide cycles Wednesday and Thursday, and could possibly continue into Friday. Coastal Flood Advisories will likely be issued starting later today.

For Beaufort, SC to McIntosh, GA Counties, the greatest risk for coastal flooding is expected with late afternoon/early evening high tide cycles today and Wednesday (~9.5 ft MLLW at Fort Pulaski, GA). Coastal Flood Advisories could be issued later today for this area.

Rip Currents/High Surf/Beach Erosion: The setup remains highly favorable for strong to dangerous rip currents today and Wednesday with breezy/gusty northeast winds expected. In addition, seas will build across nearshore waters, with 4-7 ft breakers occurring in the surf zone (largest along coastal Georgia) starting this afternoon and persisting into Wednesday. A High Surf Advisory has been issued from noon today through early Wednesday afternoon along the entire coast as a result, and could eventually need to be extended longer along Georgia beaches into later Wednesday. Significant beach erosion is likely with guidance suggesting highest chances for impacts around the afternoon/early evening high tide cycle today.

KEY MESSAGE 2: Cooler temperatures along with breezy conditions are expected during the middle of this week.

Today: A strong 1025mb surface high pressure is sliding southeastwards out of the Great Lakes region and towards the northeast coast, while an area of low pressure attempts to develop along the front south of the region over the Atlantic during the morning. Previously, models had shown higher confidence in that area of low pressure turning into an actual surface low, with that scenario trending less likely rather significantly with the recent runs. As a result, the strongest winds have decreased due to the lowered surface pressure gradient. Areas well away from the coast are still expected to see gusts to near 20 mph, while those along the coast may see gusts to 35 mph, especially along southeast Georgia beaches where the surface pressure gradient looks to be highest. Winds on Lake Moultrie are now expected to remain just below Lake Wind criteria of sustained 20 knot winds or gusts greater than 25 knots, but will continue to be monitored.

In addition to the breezy winds, temperatures will remain below normal today as h925 temperatures in the 15-17 deg C range will keep temperatures limited to the mid to upper 70s. Lastly, rain chances will be low for majority of the region today as dry air filters in from the north, with precipitable water values below an inch for areas from Millen, GA to Summerville, SC to Georgetown, SC and northwards. Areas from Reidsville, GA to Hilton Head, SC and southward have pwats remaining above 1.5", and as weak shortwaves make their way around the base of the trough some light to moderate rain will be possible. Not expecting more than a couple tenths.

Wednesday: The surface high pressure weakens as it slides down the east coast throughout the day, with the aforementioned area of low pressure pushed further south offshore of FL. This will result in weaker winds than we have for Tuesday, with gusts remaining below 20 mph for most, though areas along the coast may still gusts to near 25 mph. The exception remains across far southeast Georgia along the coast, where gusts to near 30 mph will remain possible due to the tightened pressure gradient. Chances for rainfall remain low as dry low-mid levels overspread the area.

Thursday-Friday: As weak ridging occurs aloft, dry northeasterly surface flow keeps the region dry, with another surface high pressure moving across the Ohio River Valley on Friday towards the northeast coast. Winds may again become breezy on Friday, with rainfall chances remaining uncertain.

KEY MESSAGE 3: NHC has identified a disturbance in the southwestern Gulf with a high chance of tropical cyclone formation during the next 48 hours. Regardless of development, heavy rainfall could develop over the Southeast United States by this weekend.

An area of low pressure is expected to develop over the southwestern Gulf during the next 48 hours, possibly becoming more organized and deepening while tracking northeast across the Gulf late week. Regardless of development, deep tropical moisture will likely be drawn northward across the Southeast United States with PWATs exceeding 2 inches locally. A wedge of high pressure will likely be in place across the Carolinas and Georgia while coastal troughing takes shape off the coast this weekend, supporting widespread isentropic lift across the region and the potential for heavy rainfall closer to the coast, especially as a weak front/coastal low passes nearby late weekend/early next week.

AVIATION /12Z TUESDAY THROUGH SATURDAY/

CHS/JZI: VFR conditions are expected to prevail through 12Z Wednesday. However, breezy/gusty northeast winds will develop at the terminals by around 14Z this morning and generally peak in the 20-25 kt range this afternoon into early evening hours (18-23Z). Northeast winds could remain slightly gusty through 06Z Wednesday, generally in the 10-15 kt range at CHS and in the 15-20 kt range at JZI, before remaining at or below 10 kt through 12Z Wednesday.

SAV: Low-end MVFR conditions are possible during the next couple hours as low clouds impact the terminal through ~14Z. High-end MVFR cigs should then prevail mid morning into early afternoon hours. Gusty northeast winds are expected by around 15z this morning and should generally peak between 20-25 kt this afternoon into early evening (18-23Z). Light showers could also impact the terminal during this time, potentially leading to TEMPO MVFR cigs. At this time, VCSH still remains with no restrictions. Northeast could then remain gusty through 06Z Wednesday, generally in the 15-20 kt range, before remaining at or below 10 kt through 12Z Wednesday.

Extended Aviation Outlook: VFR through late week. Breezy winds possible at all terminals on Wednesday. The risk for flight restrictions returns over the weekend with increasing chances for showers and/or thunderstorms.

MARINE

Today and Tonight: Marine conditions are expected to quickly deteriorate throughout the morning hours as a wedge of high pressure settles in, with an area of low pressure developing along a stalled front to our south. Previously, models had shown higher confidence in that area of low pressure turning into an actual surface low, with that scenario trending less likely rather significantly with the recent model runs. As a result, the strongest winds have decreased due to the lowered surface pressure gradient, with a longer period of Small Craft Advisory level winds (25-34 knot gusts) occurring prior to the potential for gale force winds (34+ knots) developing. The probability for gale force winds remains above 60% across our nearshore and offshore waters, primarily from 2 PM through midnight, so have left the Gale Warnings in place but did trim off a couple hours on the expiration times.

So for today, expect northeasterly winds to strengthen throughout the morning hours, likely seeing gusts in the 25 to 30 knot range by daybreak. 6 foot waves build in quickly due to the breezy conditions, with 4-7 ft waves along the coast throughout the afternoon and 10 foot waves in the 20-60 nm offshore zones from Edisto Beach, SC to Altamaha Sound, GA. The surface pressure gradient is expected to peak this afternoon into the evening hours producing sustained winds near 30 knots and gusts of 35 to 38 knots. The gradient is expected to weaken overnight, though still strong enough to produce gusts of 25 to 34 knots across all nearshore and offshore zones, so expect Small Craft Advisories to replace the Gale Warnings when they expire, where appropriate. For the Charleston Harbor, the Small Craft Advisory expires at 10 PM.

Wednesday-Saturday: The pinched surface pressure gradient continues into Wednesday, though the gradient does weaken throughout the day. Expect gusts of 25 to 30 knots throughout the morning hours across all zones, with winds weakening from north to south throughout the afternoon and into the evening hours. Seas will similarly subside from north to south Wednesday evening into Thursday afternoon, allowing for the expected advisories to expire. Another surface high pressure may setup along the northeast coast on Friday, potentially increasing wind speeds and wave heights across local waters into Saturday.

EQUIPMENT

The Metter, GA, NOAA Weather Radio Station (WWH-25) will be offline from mid-morning Wednesday, October 7, through the afternoon of Thursday, October 8. The transmitter is being relocated.

CHS WATCHES/WARNINGS/ADVISORIES

GA...High Risk for Rip Currents through this evening for GAZ217-219-239- 241. High Surf Advisory from noon today to 2 PM EDT Wednesday for GAZ217-219-239-241. SC...High Risk for Rip Currents through this evening for SCZ148>151. High Surf Advisory from noon today to 2 PM EDT Wednesday for SCZ148>151. MARINE...Small Craft Advisory until 10 PM EDT this evening for AMZ340. Gale Warning until 8 PM EDT this evening for AMZ360-362-380. Gale Warning until 10 PM EDT this evening for AMZ364-382-384.