textproduct: NWS Wilmington

SYNOPSIS

Hot and humid weather will persist through Monday as Bermuda High Pressure maintains a southwesterly wind across the Carolinas. A cold front arriving Monday could bring increasing coverage of showers and thunderstorms, followed by slightly cooler weather Tuesday and Wednesday. Heat could return late next week.

NEAR TERM /THROUGH SATURDAY/

Cu fields have begun to show signs of life early this afternoon and should lead to widely scattered showers/tstms through the late afternoon and early evening. HREF indicates convective activity will trail off after 02Z. Overnight min temps will only fall to the mid 70s, except upper 70s at the beaches as surface high pressure off the SE coast maintains warm and moist SW flow across the area. Synoptic features Saturday remain largely unchanged from today as a ridge continues to dominate across the SE CONUS. Guidance continues to point to widespread mid 90s Saturday, and combined with mid/upper 70s dewpoints, will necessitate another CWA-wide Heat Advisory. The heat index will likely touch 110 degrees in a few locations Saturday afternoon, but only for an hour or two, therefore not requiring an Extreme Heat Warning. The mid-level ridge will keep weak ripples in the westerly flow aloft just to our north, along with better chances for tstms. Across our CWA, PoPs Saturday will generally range from 20% across NE SC to 40% across SE NC.

SHORT TERM /SATURDAY NIGHT THROUGH MONDAY NIGHT/

A 500 mb ridge centered over the Florida Gulf Coast on Saturday Night should retrograde to the lower Mississippi Valley by late Monday. Hot temperatures and high dewpoints should continue across the Carolinas Sunday, likely necessitating another day of Heat Advisories with afternoon heat indices expected to reach 105-108 degrees. Sunday's seabreeze front and the Piedmont Trough inland should be triggers for isolated showers and thunderstorms within an airmass with 2000-3000 J/kg CAPE but with relatively dry mid level humidity.

By Monday the upper ridge should retrograde far enough to allow northwesterly mid and upper level flow to develop over the Carolinas. In addition, an upper trough swinging through New England should help push a surface cold front southward into the Carolinas during the day. High temperatures on Monday should again reach the mid 90s with high humidity, likely triggering yet another Heat Advisory. Enhanced low level convergence as the front meets the afternoon seabreeze plus impulses arriving within the northwest flow aloft should help to develop clusters of showers and thunderstorms Monday afternoon into Monday night. While we're not in a Day 4 convective outlook from SPC, it's possible strong/gusty winds could develop in association with these storms. The cold front should gradually work its way offshore Monday night.

LONG TERM /TUESDAY THROUGH FRIDAY/

The upper ridge should poke north over the Mississippi River Valley Tuesday through Thursday, perhaps settling back toward the Gulf Coast again by Friday. Low level northeast flow should bring slightly cooler air into the Carolinas Tuesday and Wednesday with highs anticipated to reach 85-90 both days with maximum heat indices only in the 90s. Uncertainties as to how far south the front makes it before stalls means I'll have to keep a chance of showers and thunderstorms in the forecast Tuesday despite the GFS showing the arrival of a drier and much more stable airmass.

The front should gradually wash out just off the Southeast coast Wednesday into Thursday as the Bermuda High strengthens offshore. This should gradually veer our surface winds from northeast to a southerly direction with humidity creeping back up each day. By Friday it's possible we'll have a return to the same airmass we're in now with temperatures in the 90s and heat indices creeping back up to the 105 trigger for Heat Advisories.

Note: although the 12z operational GFS shows a low developing from the old front and moving onshore Thursday, there is no support for this solution among the 12z GFS ensembles at this time.

AVIATION /18Z FRIDAY THROUGH WEDNESDAY/

Widely scattered showers/tstms moving into the Pee Dee region and NE SC may impact KFLO/KLBT/KMYR/KCRE over the next few hours with MVFR cig/vis and potential wind gusts to 30 kt. Convection will wane after 02Z and should remain quiet overnight. Isolated showers/tstms will begin to pop up by 16Z or so Saturday, but confidence too low to include if TAFs at this stage.

MARINE

Through Saturday...SW flow will persist through Saturday between surface high pressure off the SE coast and a weak Piedmont trough across the inland Carolinas. Wind speeds will be on the order of 10- 15 kts with occasional gusts to 20 kts, particularly this afternoon and again Saturday afternoon as the gradient tightens up a bit. Shower/tstm chances remain relatively low this afternoon and overnight, and will tick up a bit north of Cape Fear late Saturday due to proximity to the westerly flow aloft and associated weak shortwave energy crossing NC.

Saturday night through Tuesday...Bermuda High Pressure offshore will maintain a humid southwest wind across the Carolinas Saturday night through Monday. A cold front should arrive at the beaches during the day Monday, however Monday's daytime seabreeze should be strong enough to keep the front from initially pushing out across the coastal waters. We will need to watch Monday afternoon and Monday night closely for the development of clusters of gusty thunderstorms which could bring impacts for mariners. The front itself should finally push offshore Monday night with northeasterly wind expected to develop Tuesday into Wednesday. Confidence on the speed of these northeast winds is not particularly high - the 12z GFS model has a stronger high building over coastal New England by the middle of next week and shows our NE winds averaging 20 knots while the 12z Canadian and 00z ECMWF are in the 10-15 kt range.

There should be a small 8 second southeast swell with us through the entire forecast period. Dominant waves, however, will consist of a 5 second southerly wind wave Saturday night through Monday, then a 5-6 second northeasterly wind wave Tuesday into Wednesday. Combined seas should average 2-4 feet -- although higher seas could develop Tuesday and Wednesday if the GFS model is correct with its higher wind speeds.

ILM WATCHES/WARNINGS/ADVISORIES

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