textproduct: NWS Wilmington

WHAT HAS CHANGED

Aviation discussion updated for 12Z TAFs.

KEY MESSAGES

1) Heavy rain is likely late Saturday into early Sunday. Isolated flash flooding and severe weather is possible, especially near the coast.

2) Hazardous surf conditions and tidal flooding are likely this weekend.

3) Hazardous marine conditions are likely this weekend.

DISCUSSION

KEY MESSAGE 1... Heavy rain is likely late Saturday into early Sunday. Isolated flash flooding and severe weather is possible, especially near the coast.

Hurricane Isaias is currently moving northward through the Gulf and expected to make landfall Friday. Across the Carolinas, sounding data continues to show very dry air through the low to mid levels through much of tonight. Tropical moisture lifting northward on Saturday will eventually work through a stubborn dry layer with heavy rain developing by Saturday evening from south to north. Soundings show moisture working its way downward through the atmosphere with thickening clouds through Sat morning and increasing chc of pcp from south to north by mid to late morning. Models may be a bit quick on pcp onset, but there will be increasing chc of some decent rain Sat aftn and evening. Latest WPC QPF brings 2 to 4 inches of rainfall for coastal areas with lower amounts as you move westward. There should be some localized greater amounts and therefore isolated flash flooding is possible, especially in our larger coastal communities and around a higher-than-normal high tide on late Saturday through early Sunday.

Onshore flow also brings the potential for severe weather, mainly Saturday night, less so into early Sunday. Weak instability in the low levels and effective helicity may support a few onshore-moving waterspouts on Saturday night. Confidence is low at this time due to poor instability and relative distance from the storm center. Winds turn southerly on Sunday, but activity becomes more isolated with the addition of dry air. This could slightly enhance instability near the end of the event, early Sunday.

Isaias will merge into the background 500 mb flow on Sunday. Dry air building across the southeast on Sunday afternoon may push a trough through the Carolinas with some additional development along this boundary. The latest forecast extends rain chances into Sunday evening, but overall rain chances should diminish through Sunday.

KEY MESSAGE 2... Hazardous surf conditions and tidal flooding are likely this weekend.

Increasing onshore flow this weekend combining with high astronomical tides will produce rough surf, strong rip currents, and lead to minor coastal flooding for all area beaches.

Dangerous rip currents are expected as onshore flow increases late today, peaking on Saturday and Sunday. Breaking waves in excess of 5 feet are possible and will produce dangerous surf in combination with strong longshore currents. A High Surf Advisory may be needed for Saturday. Lingering rough surf is also possible on Monday, even as winds turn westerly. Beach erosion is also possible during each high tide cycle on Saturday and Sunday.

Minor coastal flooding is expected to continue along the lower Cape Fear River through the remainder of this week due to a combination of onshore winds and the new moon. Water levels will increase this weekend, but should remain within minor flood levels. The most impactful high tides are expected Saturday evening, Sunday morning, and Sunday evening. Area beaches are also expected to experience minor coastal flooding with these tidal cycles. The Saturday evening high tide is likely to be the most impactful for these areas, but each high tide cycle has the potential to produce minor flooding.

KEY MESSAGE 3... Hazardous marine conditions are likely this weekend.

See marine section.

AVIATION /09Z FRIDAY THROUGH TUESDAY/

VFR with some stronger NE winds after sunrise 5-10 kts. High clouds will thicken with slowly lowering ceilings late tonight, starting at coastal terminals first. MVFR CIGs with light/moderate showers will be possible 06Z onwards with lowest chance of restrictions at KLBT.

Extended Outlook...Flight restrictions due to low cigs are likely starting either Saturday or early Sunday as tropical moisture from Isaias works its way into the area. Vis restrictions are possible at times in heavy rain, mainly for coastal terminals from late Saturday through early Sunday. VFR should return as dry air filters in late Sunday or on Monday.

MARINE

Northeast winds will increase today as an area of high pressure to the north builds across the Carolinas. The gradient will tighten late today as Isaias makes landfall along the Gulf coast. A Gale Watch has been issued, starting early Saturday morning, as a rapid increase in winds and seas is expected. SCA conditions develop prior to the beginning of the Gale Watch, but this period of time appears to be short enough to forgo the SCA for now. Confidence is lower in SC nearshore waters depending on the location of the frontal boundary.

Latest wind probs favor the potential for sustained gales and gusts to 40 knots in the offshore waters mainly late Saturday. Winds and seas progress quickly with the northward moving front and associated gradient. SCA conditions should return for the nearshore waters as Gales diminish into late Saturday and offshore gales should end by early Sunday. Seas will build rapidly on Saturday to 6 to 8 feet for nearshore areas and 8 to 10 feet offshore by late Saturday. Seas should remain highest in northern waters north of Cape Fear and offshore.

Southerly flow remains elevated through Monday as the surface low slowly lifts toward the Mid-Atlantic and a post-frontal gradient develops. Seas may continue to exceed 6 feet through early Monday morning.

ILM WATCHES/WARNINGS/ADVISORIES

NC...Coastal Flood Advisory until 11 AM EDT this morning for NCZ107. SC...None. MARINE...Gale Watch from Saturday morning through late Saturday night for AMZ250-252-254-256. Gale Watch from Saturday morning through Sunday morning for AMZ280-284.