textproduct: NWS Wilmington

WHAT HAS CHANGED

While the key messages remain relatively similar there have been some modifications to the details noted in them.

KEY MESSAGES

1) Heavy rain will develop during Saturday and persist at times into Sunday morning. A few areas could see flash flooding as a result, especially across coastal areas. Isolated tornadoes are possible Saturday night into early Sunday.

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

3) Hazardous marine conditions are likely this weekend.

DISCUSSION

KEY MESSAGE 1...Heavy rain will develop during Saturday and persist at times into Sunday morning. A few areas could see flash flooding as a result, especially across coastal areas. Isolated tornadoes are possible Saturday night into early Sunday. Isaias is expected to make landfall along Gulf this evening and will remain far west of the forecast area. Even though it remains far to the west deep tropical moisture will overspread the area. As UVVs increase during Saturday with divergent flow expanding overhead the potential for heavy rainfall will exist especially Saturday afternoon into early Sunday morning. In fact, there are some scenarios that depict PWATs approaching 2.4 to 2.5 inches during Saturday which would rival the highest PWATs at the CHS RAOB for this time in October. While most guidance suggest a broad area of 2 to 4 inches, especially along coastal areas the HREF is showing a couple max areas greater than 10" just off the coast. Given the environment and proximity of some of the higher end rainfall amounts feel it is best to issue a Flood Watch for the coastal counties and Columbus County to start with. Additionally, there will be an opportunity with an environment supportive of tornadoes. This potential is similar across all of northeast SC and southeast NC highlighted by a Marginal (1 of 5) Risk Saturday night into early Sunday morning. A Marginal Risk is also highlighted across the forecast area during the remainder of the day Sunday but is more conditional at that time. Deeper drying during Sunday will impact the areal extent of any convection and the threat of flooding.

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

No changes to the previous thinking regarding coastal impacts this weekend. The increased onshore will yield rough surf and strong rip currents. A High Surf Advisory may be needed for Saturday due to breakers exceeding 5 ft in the surf zone, along with elevated rip current risks. Wave-runup may also cause minor to moderate beach erosion, especially those beaches with a weakened shoreline structure with high tide Saturday evening. Rough surf may linger into Monday but should improve as the winds become more favorable.

The winds coupled with the high astronomical tides during the next several high tide cycles will lead to minor coastal flooding along all area beaches and the lower Cape Fear River including downtown Wilmington. A Coastal Flood Advisory will likely be needed for high tide starting Saturday morning.

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

See marine section.

AVIATION /18Z FRIDAY THROUGH WEDNESDAY/

VFR through tonight. High clouds will thicken with slowly lowering ceilings late tonight, starting at coastal terminals first. Dry air in the low and mid levels will take some time to saturate, so lower CIGs and rain have been slightly delayed with the latest forecast. Once MVFR restrictions develop, rapid deterioration is expected through early afternoon from south to north. IFR expected near or shortly after the end of the period.

Extended Outlook... IFR conditions are likely starting Saturday evening as tropical moisture from Isaias works its way into the area. Heavy rain and thunderstorms are expected Saturday night into Sunday, higher confidence at coastal terminals. VFR should return as dry air filters in late Sunday and Monday.

MARINE

Northeast to easterly winds will increase Saturday as the pressure gradient tightens between high pressure north of the area and Isaias which will be moving farther inland after landfall along the Gulf this evening. The flow will continue to veer to the southeast and south during Saturday evening and wind speeds will likely be aided by areas of convection. While sustained winds may be marginally at or below Gale Force frequent gusts to Gale Force support replacing the Gale Watch with a Gale Warning. Seas will become steeper and increase to 7 to 10 ft, especially offshore. The flow will finally veer to an offshore direction Sunday night with speeds decreasing with improving maritime conditions during Monday. At some point the Gale Warning will need to be lowered in favor of a Small Craft Advisory, possibly during Sunday.

ILM WATCHES/WARNINGS/ADVISORIES

NC...Flood Watch from Saturday morning through late Saturday night for NCZ099-105>110. SC...Flood Watch from Saturday morning through late Saturday night for SCZ054>056-058-059. MARINE...Gale Warning from 8 AM Saturday to 6 AM EDT Sunday for AMZ250- 252-254-256-280-284.