textproduct: Newport/Morehead City

WHAT HAS CHANGED

Aviation section updated for 00Z TAF issuance. High Surf Advisory has been issued for Ocracoke and Hatteras Islands from Saturday night into Sunday evening.

KEY MESSAGES

1) Wet weekend is expected as moisture associated with TC Isaias overspreads the Carolinas. Heavy rain is likely with highest amounts focused along the coast.

2) A few stronger thunderstorms are possible on Sunday.

3) Coastal impacts possible this weekend.

DISCUSSION

KEY MESSAGE 1...A plume of tropical moisture characterized by 2"+ PWATs and dewpoints in the 70s is forecast to get pulled north through the Southeast U.S. over the weekend to the east of the northward-advancing remnants of TC Isaias. At the surface, a warm front will trudge north along the Southeast U.S. coast, potentially with a weak, non-tropical area of low pressure developing along it. Along and ahead of the warm front, a strong southeasterly LLJ will develop, supporting increasing WAA and moisture transport into the area with a shield of moderate to heavy rain developing across the coastal Carolinas. It's expected that this initial swath of precip should support 1-2" of rainfall for much of ENC. Along and just behind the warm front, the precip may become more banded in nature, including with some embedded convective elements. It's these bands that will pose the most intense rainfall rates, as well as the greatest risk of flooding. Convective guidance suggests rainfall amounts as high as 3-6"+ are possible if those bands manage to reach the coast. As is often the case in these scenarios, it's unclear how far inland the instability axis and, consequently, the heaviest rates will get. The higher end rainfall scenario is worth mentioning, but it should also be understood that those amounts are unlikely to be realized if the instability axis remains offshore.

As far as model guidance goes, it's also worth noting that the majority of guidance has trended higher with rainfall totals, and the latest forecast amounts reflect this trend. Additionally, various ensemble and forecast aids show a notable signal for heavy rain. A Flood Watch may eventually be needed for a portion of the area if confidence increases regarding the higher end rainfall totals.

KEY MESSAGE 2...Steady increase in moisture through the weekend peaks on Sunday contributing to an increase in instability across portions of ENC, greatest south of Highway 264. Factors like cloud cover will determine how much we end up getting, but ensemble averages suggest CAPEs as high as 1000+ J/kg in some spots. While low- level forcing is in question, it's a setup that bears watching for a conditional severe thunderstorm risk. Machine learning guidance and EFI guidance have changed little from yesterday, still suggesting at least a marginal threat.

The remnants of Isaias are forecast to round the upper level ridge and move off the Northern Mid-Atlantic Coast early next week. Drier air then moves in behind it with a lower chance of showers and thunderstorms by Tuesday.

KEY MESSAGE 3...Strengthening onshore winds, building seas, and higher astronomical tides may support some coastal impacts this weekend. There is some uncertainty on the magnitude of impacts, especially given the shorter-duration of the stronger winds, as well as what should be a weaker swell compared to the recent Nor'easter. With that in mind, there will be an increased risk of rip currents and large waves, at minimum. With this in mind, have issued a High Surf Advisory for Ocracoke and Hatteras Islands, the locations most likely to see 8ft waves in the surfzone from late Saturday night through around sunset on Sunday. Additionally, some of the most vulnerable locations along the Outer Banks may see at least some minor issues, especially with Sunday morning's high tide (7-9am). There may also be some minor coastal flooding around sounds and tidal waterways around the Crystal Coast due to the higher astronomical tides.

AVIATION /00Z FRIDAY THROUGH TUESDAY/

Forecast confidence is high over the next 24 hours.

VFR conditions are expected to prevail through the 00z TAF cycle, with mostly high level cirrus overhead. A few low cumulus clouds may develop at times, but low CIGs are not expected. Once again, some MIFG/BR may develop overnight, especially in the vicinity of OAJ, but a deep/impactful FG is not expected. Light SW winds today are expected to become northeasterly on Friday.

Outlook: Conditions change over the weekend as tropical moisture gets pulled north off the Gulf and into the Carolinas. This will support periods of low CIGs, widespread RA, and potentially a TSRA risk. Gusty southeast to south winds are likely as well, especially Saturday into Sunday along the Outer Banks.

MARINE

Good boating conditions are expected to continue for at least 1 more day as high pressure remains overhead and winds are generally at, or below, 10-15kt. The one caveat is that northeasterly winds will build some during the day Friday, and may approach 15-20kt by the afternoon hours, especially north of Cape Hatteras.

Outlook: A strong pressure gradient develops in advance of a warm front and a weak, non-tropical, low that is forecast to lift north along the Southeast U.S. coastline this weekend. It's likely that this will support a period of moderate to strong east to southeast winds Saturday into Saturday night, followed by a period of moderate to strong south to southwest winds Sunday into Sunday night. Most waters should reach Small Craft Advisory criteria (25kt gusts), but there is the potential for some waters to reach gale-force winds. Confidence in gales is highest south of Cape Lookout, and a Gale Watch is now in effect for those coastal waters. Additional marine headlines will eventually be needed, including the potential for the Gale headline to be expanded. In addition to the winds, seas are expected to peak in the 6-9ft range at 7-8s. For the outer coastal waters, seas may reach 8-10ft.

Thunderstorms capable of strong winds and waterspouts will be possible as well, mainly Saturday night into Sunday.

Conditions gradually improve early next week as high pressure builds in behind the weekend system.

MHX WATCHES/WARNINGS/ADVISORIES

NC...High Surf Advisory from midnight Saturday night to 8 PM EDT Sunday for NCZ204-205. MARINE...Gale Watch from Saturday morning through Sunday morning for AMZ158-188.