textproduct: NWS Wilmington

WHAT HAS CHANGED

Aviation discussion updated to reflect changing conditions. Heat Advisory expanded to include areas along and west of I-95.

KEY MESSAGES

1) Dangerous heat to continue at least through today.

2) Isolated severe storms and flash flooding possible on Friday.

DISCUSSION

KEY MESSAGE 1...Dangerous heat to continue at least through today.

Well-above normal temperatures will continue through today before scattered to numerous showers and thunderstorms and associated cloud cover bring slightly cooler high temperatures on Friday. As with the last few days, the main concern for today is whether enough dry air will mix down from aloft to prevent 105F heat indices from occurring for 2+ hours. However, with only isolated showers and perhaps a gusty thunderstorm expected, and this being the 9th day in a row with a heat headline out, have opted to lean into the accumulating effects of prolonged heat to justify expanding the Heat Advisory into the rest of the area, regardless of whether the heat indices just miss or nudge into the 105F criteria. Outdoor workers and others performing activities outside should take necessary precautions to prevent heat- related illness today as rain and substantial cloud cover will be lacking.

Heat indices reaching above 105F are possible again on Friday for parts of the area before showers and thunderstorms develop. While this may require another Heat Advisory, the anticipated showers and thunderstorms should result in an earlier end to the high heat indices due to rain and cloud cover.

KEY MESSAGE 2...Isolated severe storms and flash flooding possible on Friday.

A trough in the jet stream and attendant cold front progressing eastward into the Carolinas on Friday should yield scattered to numerous showers and thunderstorms, with a low risk for strong to severe wind gusts. Bulk shear across the 0-6 km layer is only forecast to run 10-15 knots on Friday, with up to around 20 kts possible across northern areas, leading to any severe weather risk being sporadic and reserved to the strongest storms of the day. Storm motions are expected to range in the 10-20 kt realm, leading to some risk for flash flooding, especially if multiple storms track or merge over the same areas. Plenty of moisture in the atmosphere with precipitable water values around 2-2.2" can easily yield heavy rain rates of 1-2" per hour or even greater in the strongest storms. Inland areas should have the highest coverage of storms, with sea breeze passage keeping coastal areas mostly dry until Friday night. Another round of showers and thunderstorms appears likely on Saturday as the front slides farther southeast into the area, with a greater emphasis along the coast.

AVIATION /08Z THURSDAY THROUGH MONDAY/

An expanding fog and low cig bank is observed over the area with MVFR to LIFR restrictions occurring at an increasing number of AWOS and ASOS sites. The threat for a period of restrictions has increased substantially given the extent of this fog/low cigs and amendments will be made to the TAFs as this evolves. VFR will return within 1-3 hours of sunrise depending on the thickness of the fog/low stratus.

Otherwise, expect VFR through the remainder of the period with isolated pop-up showers and thunderstorms (and attendant vis restrictions) carrying a low chance (<30%) to impact a terminal. Guidance has tended to be too aggressive on coverage the last few days, so I am hesitant to include PROB30s today as similar conditions that typically limit convection are still in place today. Expect VFR to continue through 06Z tonight before fog chances increase later in the night.

Extended Forecast... Brief MVFR/IFR conditions are possible in areas of ground fog or low stratus late tonight/Friday morning as well as Saturday night/Sunday morning.

Chances for thunderstorms and related MVFR to LIFR vis restrictions will become moderate to high Friday afternoon and again Saturday afternoon as a cold front approaches the eastern Carolinas. Scattered thunderstorms may continue through Sunday and Monday, mainly in the afternoons near the coast affecting KILM, KCRE, and KMYR as the stalled front decays.

MARINE

Today through Monday... Light south winds today will focus out of the southwest tonight as a cold front approaches from the northwest. Expect generally south to southwest winds to persist through the period as the front stalls near the coast on Saturday. Wave heights around 1-2 ft through Friday are expected to rise slightly in tandem with stronger winds over Friday night to 2-3 ft in the 0-20nmi zones and 3-4 ft in the 20-60nmi zones for Saturday through Sunday before lowering slightly on Monday. Wind waves will be a primary contributor the wave spectrum while a 1ft ESE swell with a period around 8 sec is expected through the period as well.

The biggest marine impact will likely be from increasing coverage of showers and thunderstorms beginning Friday evening and continuing through the weekend as a front stalls near the coast. There will likely be several rounds of storms, accompanied by reduced visibility and possible gusty winds.

ILM WATCHES/WARNINGS/ADVISORIES

NC...Heat Advisory from 11 AM this morning to 8 PM EDT this evening for NCZ087-096-099-105>110. SC...Heat Advisory from 11 AM this morning to 8 PM EDT this evening for SCZ017-023-024-032-033-039-054>056-058-059. MARINE...None.