textproduct: Philadelphia/Mt Holly

WHAT HAS CHANGED

A Coastal Flood Advisory has been issued for tonight's high tide cycle for portions of southern NJ and the Delaware Bay.

A Rip Current Statement has been issued for Thursday for all Jersey Shore beaches.

KEY MESSAGES

1. Scattered showers and thunderstorms will be possible today.

2. Severe thunderstorms possible Thursday afternoon and evening, along with windy and hotter conditions.

3. Tide levels will remain elevated through tonight's high tide cycle, which may lead to areas of spotty minor to minor tidal flooding.

DISCUSSION

KEY MESSAGE 1...Scattered showers and thunderstorms will be possible today.

A stationary front over the Mid-Atlantic will lift north as a warm front as low pressure over the Great Lakes tracks east. As the front lifts north this afternoon, it will interact with some midlevel shortwave energy that will support a few isolated showers and thunderstorms, mainly northwest of I-95. No severe thunderstorms are expected.

Today will be warmer with highs in the low to mid 80s and surface dewpoints will creep up into the upper 50s to low 60s, making it feel a bit more humid than previous days.

KEY MESSAGE 2...Severe thunderstorms possible Thursday afternoon and evening along with windy and hotter conditions.

A closed upper-low over portions of Manitoba and Ontario will continue to meander in that region, with large scale troughing in place over much of the Northern CONUS. On Thursday, a strong shortwave still appears poised to round the base of the trough, ejecting through southern portions of Ontario and Quebec southward into New England, taking on an increasingly negative tilt as it does so. A belt of enhanced flow aloft will overspread the region as the shortwave passes to the north. At the surface, a warm front looks to lift through the area during the early morning hours. Low pressure looks to track north of the region with a tailing cold front passing through the region during the afternoon and into the evening hours.

Showers and perhaps a few elevated thunderstorms associated with decaying convection from upstream appear likely during the morning hours across primarily east central PA and northern NJ. Severe weather appears unlikely with this initial round of activity. Southeastern PA, central and southern NJ, and the Delmarva will likely remain dry through the morning and into the afternoon. This morning activity and its associated cloud cover will likely work to limit destabilization for our northern areas, depending on the exact timing, which should also limit coverage and intensity of any convection later in the day.

As the shortwave and cold front begin to approach the region Thursday, unseasonably strong flow at nearly all levels of the atmosphere will overspread the region. Guidance suggests H5 flow on the order of 60 kts or greater. This will lead to deep layer shear on the order of 50-55 kt. Low level flow looks to increase to around 30-40 kts, which is near the climatological maximum value for nearby RAOB sites (above the 90th percentile). Ahead of the cold front, temperatures appear likely to surge into the upper 80s to lower 90s with strong southwesterly low- level flow. In addition, moisture will continue surging into the area, with dewpoints rising into the upper 60s to near lower 70s, though at least modest mixing does appear probable with the strong surface heating. The result will be at least some destabilization, with guidance generally depicting MLCAPE values around 1000 J/kg.

Latest guidance has trended a little faster with the shortwave, with both the GFS and NAM showing it passing north of the area mid- morning into early afternoon. The ECM continues to feature a slightly slower northeastward progression of the wave, with it passing north of the region during the afternoon. This will be an important detail to monitor, as it will play a role in storm coverage along and ahead of the cold front. If the wave does indeed pass through earlier in the day, despite the flow remaining enhanced aloft, subsidence in the wake of the wave could make storm development a little more difficult. Nevertheless, the strong cold front should still be able to serve as a focus for isolated to scattered storm development. Given the destabilization, steep low level lapse rates, mid level dry air leading to higher DCAPE, and impressive kinematics, any storms that do develop will have the potential to be severe. The primary threat still appears to be damaging winds, but some instances of hail are possible given the strong yet unidirectional shear.

Outside of the severe thunderstorm potential, it will also be a hotter and windy day. With temperatures in the upper 80s to lower 90s and dewpoints in the upper 60s to lower 70s, heat indices in the low to mid 90s are likely for the I-95 corridor and points south and east, with drier and slightly cooler conditions to the northwest. The surface low that is expected to track north of the area will be fairly deep, likely around 990 mb or perhaps a bit deeper. This will lead to a strong mass response with intensifying southwesterly flow into the afternoon. As of right now, it appears southwest sustained winds of 15-25 mph and wind gusts of 30-35 mph will be common areawide, with peak gusts near 40 mph or even 45 mph in some areas. It still appears unlikely that Wind Advisory criteria will be met, but it will be noticeably and unusually windy by mid June standards.

KEY MESSAGE 3...Tide levels will remain elevated through the high tide cycle tonight, which may lead to areas of spotty minor to minor tidal flooding.

After the New Moon on Sunday, the elevated astronomical tides will continue to slowly subside. However, minor coastal flooding is still expected with tonight's high tide, primarily across the southern NJ Atlantic coast and portions of the Delaware Bay. A Coastal Flood Advisory has been issued for Cape May, Cumberland, and Salem Counties in NJ, as well as New Castle County in DE for the upcoming high tide cycle.

AVIATION /21Z WEDNESDAY THROUGH MONDAY/

The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas.

Today...Prevailing VFR, but VSBY restrictions possible in scattered afternoon SHRA/TSRA, mainly at KRDG/KABE/KTTN. South winds around 10 kts with a few gusts up to 20 kts possible through 00Z. High confidence in prevailing conditions, low chances on and SHRA/TSRA impacting any terminals directly. Will maintain PROB30 groups.

Tonight...VFR. South to southeast winds 5-10 kts, increasing some toward 12Z. LLWS developing after 06Z, with FL020 winds increasing to 35-40 kts. A few light showers possible north of PHL after 06Z, but these are unlikely to cause any restrictions. High confidence in prevailing conditions.

Thursday...Prevailing VFR, but a brief period of restrictions is possible after 18Z showers and some thunderstorms increase in coverage. Southwest winds increasing to 20-25 kts, gusting 30-35 kts outside of any thunderstorms. High confidence in prevailing conditions.

Outlook...

Friday...A few showers and thunderstorms may linger with some restrictions possible at times, but VFR should generally prevail.

Saturday through Sunday...VFR. No significant weather.

Monday...Restrictions likely in showers and thunderstorms.

MARINE

No marine hazards through tonight. South winds 10 to 15 kt with gusts up to 20 kt later today and tonight. Seas will average 2 to 4 feet.

A Small Craft Advisory remains in effect for Thursday through Thursday evening. South winds increase to 15 to 25 kt with gusts up to 30 kt. Brief gale force wind gusts near 35 kt are possible along the nearshore coastal waters (within 5 miles of the coast) during the afternoon hours. Scattered thunderstorms could also produce brief gale force wind gusts during the afternoon and evening hours. Significant wave heights building 4-7 feet through the afternoon hours.

Winds and seas will lessen Thursday night.

Outlook...

Friday through Sunday... winds and seas continue to diminish with no marine hazards anticipated.

Monday...Advisory conditions likely developing, with gusts over 25 kts and seas over 5 feet.

Rip Currents...

A Rip Current Statement has been issued for Thursday for all Jersey Shore beaches.

Thursday, south-southwest winds will be increasing to around 15 to 20 mph with gusts as high as 25 to 35 mph in the afternoon. There will be a southeasterly 4 to 6 foot swell at 6 to 7 seconds. Breaking wave heights of 2 to 4 feet anticipated for the Jersey Shore, with 1-3 feet for Delaware Beaches. As a result, have maintained the HIGH risk for the Jersey Shore and a MODERATE risk for the Delaware Beaches for the development of dangerous rip currents.

Friday, west-southwesterly winds generally 5-15 mph. There will be a south-southeasterly swell of 3 to 5 feet at around 7 seconds. Breaking wave heights of 1 to 3 feet are anticipated. Have opted for a MODERATE risk for the Jersey Shore and a LOW risk for Delaware beaches for the development of dangerous rip currents, where flow is more offshore.

For specific beach forecasts, visit weather.gov/beach/phi

PHI WATCHES/WARNINGS/ADVISORIES

PA...None. NJ...Coastal Flood Advisory from midnight tonight to 4 AM EDT Thursday for NJZ016. High Risk for Rip Currents from Thursday morning through Thursday evening for NJZ014-024>026. Coastal Flood Advisory from 9 PM this evening to 3 AM EDT Thursday for NJZ021-023. DE...Coastal Flood Advisory from midnight tonight to 4 AM EDT Thursday for DEZ001. MD...None. MARINE...Small Craft Advisory from 6 AM Thursday to midnight EDT Thursday night for ANZ430-431-450>455.