textproduct: NWS Wilmington

WHAT HAS CHANGED

Aviation discussion updated for the 12Z TAFs.

While only isolated showers are storms are expected today based on the broader pattern, there is low to moderate confidence that the favorably-timed arrival of a moisture plume from T.S. Bertha could provide a more supportive environment for the sea breeze to produce scattered showers and storms from around midday into this afternoon.

KEY MESSAGES

1) Hot weather continues through Wednesday with another Heat Advisory possible.

2) Highest chances for rain arrive with a strong cold front during mid to late week, including a risk for flash flooding.

3) A period of enhanced winds and seas will occur through midweek as a strong cold front drops down from the north, creating hazardous conditions for small craft.

DISCUSSION

KEY MESSAGE 1...Hot weather continues through Wednesday with another Heat Advisory possible.

For today, low to moderate confidence exists that the passage of a moisture plume associated with T.S. Bertha during this morning into the early afternoon will result in the sea breeze becoming active by around midday, producing scattered showers and storms which would prevent many areas from reaching Heat Advisory criteria. However, if convection remains isolated or doesn't materialize, the moisture plume should support reaching a 105F or greater heat index for 2+ hours across the advisory area. Meanwhile, the western tier of counties is expected to remain on the periphery of this moisture plume, with lower dew points expected to mix down during the afternoon as drier air filters in aloft.

The region will remain sandwiched between mid-upper troughing to the north and the closed mid-upper low associated with T.S Bertha to the south, leaving a weak ridge axis in between. Temperatures in the low- mid troposphere are forecast to hold at similar levels to those observed over the weekend, supporting continued above-normal temperatures and heat indices breaching 100F. The extent of cloudiness and showers/storms will affect whether some areas reach heat indices of 105F, but it appears additional Heat Advisories are possible until a cold front settles into the area on Thursday. Until then, coverage of showers/storms should remain isolated through Wednesday.

KEY MESSAGE 2...Highest chances for rain arrive with a strong cold front during mid to late week, including a risk for flash flooding.

As a moisture plume associated with T.S. Bertha passes through the area today, low to moderate confidence exists that this will reduce dry air and subsidence enough in the low-mid troposphere to support an active sea breeze with scattered showers and storms developing around midday and lifting northeastward through the afternoon. With pwats rising from ~1.7-1.8" to 2.1-2.2" and low to mid-level flow largely parallel to the sea breeze, heavy rainfall and training thunderstorms capable of producing localized flash flooding in low- lying and poor drainage areas would be the main hazard if more than the typical isolated pop-up storms materialize.

Otherwise, if remnant dry air and subsidence win out, isolated showers and storms remain a possibility through Wednesday along the sea breeze and any convergence zones that happen to form inland. An isolated strong to damaging wind gust cannot be ruled out if a storm can take advantage of steep low-level lapse rates combined with a heavy, water-loaded downdraft. Something to watch is the progression of showers and storms to the north, which could send outflow into our northern tier of counties (Pender through Marlboro) and produce areas of heavy showers and storms.

As troughing becomes reinforced over the eastern CONUS during midweek, a stronger cold front is progged to push slowly southward into the area on Thursday or Thursday night before stalling. This front, accompanied by occasional mid-level shortwaves helping to enhance lift, is likely to result in periods of scattered to numerous heavy showers and storms into this weekend. The primary threat this setup will bring is flash flooding from heavy storms backbuilding and/or tracking over the same area multiple times.

KEY MESSAGE 3...A period of enhanced winds and seas will occur through midweek as a strong cold front drops down from the north, creating hazardous conditions for small craft.

See marine discussion below.

AVIATION /12Z TUESDAY THROUGH SATURDAY/

CIGs should start to scatter out at the start of the period with S winds ~8-10 kts. These will increase quickly into mid morning with gusts 25-30 kts, highest at the coast as a sea breeze moves through coastal terminals ~15-16Z. Coverage may be better than we have seen for showers/storms with the sea breeze, so coastal terminals could see brief MVFR/IFR. Strong SW winds will continue into tonight with gustiness lingering after sunset as a front approaches.

Extended Forecast...Potential for brief MVFR/IFR from storms will gradually increase beginning Wednesday and remain possible through Saturday, mainly in the afternoon and evening. More solid restrictions may arrive Thursday with a frontal passage bringing the potential for IFR CIGs.

MARINE

Tuesday through Sunday...Steady south to southwest winds are expected through midweek with daily enhancements nearshore due to the sea breeze. An approaching cold front will help tighten the pressure gradient from Tuesday afternoon into Wednesday night, resulting in a Small Craft Advisory with winds and seas firmly above criteria. Winds diminish overnight Wednesday into Thursday as a cold front drifts in from the north and stalls along or inland of the coast. Guidance now suggests the front may not push through the waters until Saturday night or Sunday, but its presence near the coast can result in changeable wind directions as at least one weak wave of low pressure ripples along the boundary.

Seas around 2 to 4 ft early today will rise to 4 to 6 ft by this evening, remaining elevated through late Wednesday. Seas will diminish to 2 to 4 ft on Thursday as winds weaken. Marine conditions should remain below any thresholds with lower winds and seas as the cold front remains in vicinity. However, periods of scattered to numerous showers and storms are anticipated due to the front, resulting in hazardous conditions for small craft in and near thunderstorms through this weekend.

ILM WATCHES/WARNINGS/ADVISORIES

NC...Heat Advisory from 11 AM this morning to 7 PM EDT this evening for NCZ087-096-099-105>110. Beach Hazards Statement through this evening for NCZ106-108. High Risk for Rip Currents through this evening for NCZ110. SC...Heat Advisory from 11 AM this morning to 7 PM EDT this evening for SCZ017-024-033-054-058-059. Beach Hazards Statement through this evening for SCZ054-056. MARINE...Small Craft Advisory from 11 AM this morning to 10 PM EDT Wednesday for AMZ250-252-254-256.