textproduct: NWS Wilmington

WHAT HAS CHANGED

Discussions updated. The speed and track of Isaias will influence how quickly rain arrives on Saturday. The current trend is a faster and further east landfall on the Gulf Coast, which could lead to an earlier start to rain on Saturday.

KEY MESSAGES

1) While unsettled weather is likely this weekend, confidence in rainfall amounts remains limited.

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

DISCUSSION

KEY MESSAGE 1...While unsettled weather is likely this weekend, confidence in rainfall amounts remains limited.

All eyes are on Tropical Storm Isaias as conditions are favorable for it to organize and strengthen in the Gulf over the next few days. While questions remain around its track and intensity, tropical moisture will lift out of the Gulf well to the east of the system and lead to a period of rainfall across the region this weekend. With a strengthening high pressure center north of the area, its attendant dry air aloft leads to the question of how long it will take for rainfall to make it to the ground. Typically, the abundance of dry air aloft keeps measurable rain at bay for longer than models suggest, which would keep much of Saturday's daytime dry, except perhaps for far southern portions of our area (Williamsburg and Georgetown counties). This will be monitored closely over the coming days as the track and speed of Isaias will influence the outcome, with a faster and further east track leading to rain starting earlier than currently anticipated.

Beyond the start time of rain, amounts also carry limited confidence depending on where bands of heaviest rain set up. In general, it appears coastal areas are favored for the highest totals, mainly in the range of 1-3 inches with locally higher amounts possible while inland areas see less, mainly around 0.5-1.5 inches. The presence of tropical moisture, with precipitable water values in the range of 2- 2.5", leads to a slight risk (level 2 out of 4) for bands of excessive rainfall capable of producing flash flooding over the coastal areas, mainly focused from late Saturday into Sunday morning. Where these bands of heavier rain occur, rainfall totals as high as 4-6" are not out of the question given the anomalous moisture in place and potential for heavy rainbands to stay over the same area for multiple hours.

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

A period of breezy onshore winds will make for both hazardous marine conditions and tidal flooding through this weekend. See the marine discussion below for more details on timing of the marine impacts. Low-end minor tidal flooding is expected to remain a concern at downtown Wilmington for the next several high tide cycles before stronger onshore winds pile water up against the coast, bringing the threat to all beaches starting with the Saturday morning high tide.

AVIATION /18Z WEDNESDAY THROUGH MONDAY/

VFR is expected to prevail through the TAF period with light winds and clear skies below 12kft. Although calm winds are expected all night tonight, abundant dry air just above the ground should keep any shallow ground fog from growing vertically. Otherwise, broken high clouds are expected to nudge back in tonight and continue into Thursday, with light winds persisting.

Extended Outlook...VFR through at least Friday evening, outside of any patchy/shallow early morning fog. Flight restrictions due to low cigs are likely starting either Saturday or early Sunday as tropical moisture from Isaias works downward. Vis restrictions are possible at times in heavy rain, mainly for coastal terminals from late Saturday through Sunday. VFR should return as dry air filters in late Sunday night or on Monday.

MARINE

Winds and seas will continue decreasing into Thursday, with flow remaining northeasterly. Benign marine conditions continue into Friday before the pressure gradient starts to tighten between Isaias and the strengthening high pressure area over the Northeast US. Northeasterly flow will start increasing on Friday and headlines are likely to be required by late Friday night as gusts exceed 25 kts and seas build to between 6 and 8 feet in the coastal waters on Saturday. Winds will veer to easterly Saturday afternoon and then southeast to south on Sunday. Peak gradient winds appear to occur from Saturday afternoon through the night with sustained speeds around 25-30 kts and gusts near or just below gale force. The easterly to southeasterly onshore flow will make for dangerous conditions to small craft in the coastal waters. So while marine conditions will be nearly ideal Thursday and Friday, expect conditions to quickly turn treacherous this weekend.

ILM WATCHES/WARNINGS/ADVISORIES

NC...Coastal Flood Advisory from 6 PM to 10 PM EDT this evening for NCZ107. Beach Hazards Statement until 8 PM EDT this evening for NCZ108. SC...Beach Hazards Statement until 8 PM EDT this evening for SCZ056. Coastal Flood Advisory until 7 PM EDT this evening for SCZ054- 056. MARINE...None.