Marine Weather and Tide Forecast for Nags Head, NC

KEY MESSAGES
1) Multiple rounds of showers and thunderstorms expected to impact eastern NC through at least Friday and potentially into the weekend as a slow-moving and moisture-laden front slowly moves across the area and stalls. Rainfall totals of up to 4-6" possible.

2) A few strong thunderstorms are possible this afternoon mainly along and north of Highway 64 with damaging winds being the primary risk. An isolated tornado is possible.

DISCUSSION
KEY MESSAGE 1...Latest analysis depicts broad troughing over the eastern CONUS this morning with a slow moving cold front oriented from southeastern Canada to just west of the spine of the Appalachians and into the southern plains. The cold front is expected to slowly make its way eastward towards the Carolinas and eventually stall, while multiple shortwaves migrate through the upper trough. This alone would already be a concern for an extended period of unsettled weather, but an additional factor to consider is a plume of deep tropical moisture, associated with TS Bertha roughly 750 mi to our WSW, forecast to advect and pool ahead of the front resulting in PWATs north of 2.25" across much of the area.

With the aforementioned synoptic setup, as well as model soundings depicting a deep warm cloud layer, ample instability but skinny CAPE profiles, and likely training storm motions, the local environment is primed for a flash flooding threat despite long-term antecedent drought conditions. Timing of rainfall onset remains uncertain with a decent amount of spread still present in CAMS, although general consensus is the threat beginning overnight Wednesday along and north of Highway 64, gradually filling in to the south into the day Thursday.
Guidance points to a drier airmass intruding into northern zones late Thursday night, but deeper moisture remains pooled south of this line and especially over the Crystal Coast through Friday-Saturday and potentially longer.

Forecast storm total amounts for the area currently range from 4-6" through Saturday night. The most likely period for the most intense rainfall is Thursday into Thursday night, and this is supported by the ECMWF EFI which continued its trend from yesterday of exceeding the 80-90% percentile of forecast precipitation. SOT values of 1-2 point to some risk for a higher-end event beyond what is forecast. It should be noted that since this will be a convective episode, showers and thunderstorms will be hit-and-miss through the period in contrast to a total washout. That being said, the environment will be highly favorable for rainfall rates of 2-3" an hour, potentially higher in more robust thunderstorms. In urban areas or highly vulnerable locations, this could quickly bring flooding concerns.

Despite uncertainty in frontal progression timing, the highly favorable environment for flash flooding necessitated a Flood Watch for the entire FA. Areas along and north of Highway 64 are valid until 12Z Friday, while areas south are valid until 00z Saturday. Extensions are possible into the weekend, especially along the southern coast. WPC maintains our area in a Slight (Level 2/4) risk of excessive rainfall for tonight, and a Moderate (Level 3/4) risk on Thursday. Slight risk remains for the area into Friday and Saturday as well.

KEY MESSAGE 2...The front tonight will be accompanied by an uptick in shear, although there will be poor forcing across our area as well as potentially limited instability with lingering cloud cover. Still, CAMs and AI NWP point to a marginal risk of a stronger storm or two, most likely across southeastern VA but potentially extending into the Albemarle Peninsula and areas north of Highway 264. Most likely timing is after 20z with damaging wind gusts being the primary threat, but an isolated tornado is possible as surface winds back ahead of the approaching front.

AVIATION /12Z WEDNESDAY THROUGH SUNDAY/
VFR conditions across TAF terminals this morning with plenty of cirrus still aloft and low stratus still trying to creep northward especially across the inner coastal plain. Low stratus will likely linger into mid-morning before increased mixing boosts cigs back to VFR. Iso scattered showers and storms possible in the afternoon and evening, but coverage likely to increase from north to south after 06z as front pushes south and interacts with deeper moisture. MVFR cigs likely to follow, but with expected torrential rainfall frequent drops of visibility to IFR or worse levels is possible.

Outlook (Thu morning through Sunday): A stronger front approaches into Thurs, renewing stronger shower and thunderstorm chances WED. This front will stall offshore on Thurs evening where it will linger into the weekend, keeping rain and subVFR flight cat threat up through this weekend.

MARINE
Regional observations depict robust small craft conditions across all area waters with southwest winds of 20 to 30 kt with occasional gusts to 35 kt. Offshore, seas have responded by building up to 6-8 feet with likely higher waves beyond 20-40 nm especially north and east of Cape Hatteras. Little change was made to existing headlines apart from an extension of most SCAs for a few hours, as timing of front responsible for the strong gradient winds has slowed somewhat. A few gusts to 35 kt remain possible across portions of the Pamlico Sound through sunrise.

Stronger winds ebb after sunrise but SCA conditions likely to persist across all zones into tonight. Shower and thunderstorm coverage likely to be limited but blossom overnight into Thursday ahead of the approaching front.

Outlook (Wednesday night through Sunday): For the outer waters, elevated winds and seas will continue into Thurs as front slowly pushes across area waters, keeping elevated winds and seas in place and increased tstorm chances. Front moves through by Thurs afternoon and evening with winds shifting to a NE'rly direction and easing to a 10-15 kts with seas falling to 2-5 ft. Winds will remain benign but front will linger over area waters into Saturday promoting an elevated risk of showers and thunderstorms over the region, especially along and south of Cape Hatteras.

MHX WATCHES/WARNINGS/ADVISORIES
NC...Flood Watch from late tonight through Friday morning for NCZ029-044>047-079>081-203.
Heat Advisory from 11 AM this morning to 7 PM EDT this evening for NCZ080-081-090-092-094-193-194-198-199.
Flood Watch from Thursday morning through Friday evening for NCZ090>092-094-193>196-198-199-204-205.
Beach Hazards Statement through this evening for NCZ195-196- 199-204-205.
MARINE...Small Craft Advisory until 2 AM EDT Thursday for AMZ131-230- 231.
Small Craft Advisory until 11 AM EDT Thursday for AMZ135-152- 154-156-158.
Small Craft Advisory until 5 AM EDT Thursday for AMZ136-137.
Small Craft Advisory until 8 AM EDT Thursday for AMZ150.
Gale Warning until 11 AM EDT this morning for AMZ180-182-184.