textproduct: Philadelphia/Mt Holly

WHAT HAS CHANGED

The Coastal Flood Warnings and Advisories for Delaware Bay and Atlantic coastal New Jersey and Delaware were extended in time to cover high tides through Friday evening.

A Coastal Flood Advisory was issued for portions of Maryland's Eastern Shore.

The Wind Advisory for Atlantic coastal New Jersey and Delaware was extended in time through Thursday evening.

The Gale Warning for the Atlantic coastal waters was extended in time through Thursday night.

A Storm Watch was issued for all offshore waters Thursday night through Saturday.

Aviation section updated for 12Z TAFs.

KEY MESSAGES

1. Light rain will continue to impact Delmarva and far southern New Jersey through this morning.

2. A strengthening surface low off the Eastern Seaboard will keep persistent northeast to north flow in place through at least Friday. Depending on the track of the low, it could bring increased rainfall chances and windy conditions to the parts of the region Friday and into the weekend.

3. Multiple rounds of significant tidal flooding expected for this week. Coastal Flood Warnings and Advisories issued.

4. Dangerous rip currents and high surf are expected at the Jersey Shore and Delaware Beaches through the end of the week. Significant beach erosion is also likely. Breaching of sand dunes is possible.

DISCUSSION

KEY MESSAGE 1...Light rain will continue to impact Delmarva and far southern New Jersey through this morning.

High pressure well to the north continues to push its influence southward across the area. However, there remains broad diffluence aloft that is sufficient to keep a band of light rain extending into Delmarva and southern New Jersey. The upper forcing for ascent looks to wane by dawn, and thus the band of rain should dissipate by 9-10 AM.

KEY MESSAGE 2...A strengthening surface low off the Eastern Seaboard will keep persistent northeast to north flow in place through at least Friday. Depending on the track of the low, it could bring increased rainfall chances and windy conditions to the parts of the region Friday and into the weekend.

A mid-level trough currently traversing portions of the Midwest into the Ohio Valley will continue eastward and amplify towards the Eastern Seaboard today. Weak surface cyclogenesis has begun off the coast of the Carolinas, with the low expected to continue intensifying through late this week. The initial track of the developing low is expected to be to the northeast, well offshore. However, with a strong high centered over portions of Quebec, a sharp pressure gradient over the region will at least lead to breezy conditions through Thursday. The strongest pressure gradient, and thus winds, are forecast to occur on today into tonight. It should remain mostly dry today (following the early morning light rain) through Thursday.

Given a consistent forecast for sustained northeast winds 25-35 mph along the Atlantic coasts of New Jersey and Delaware today, the Wind Advisory remains in effect for the immediate coastal strip. This was extended in time through 8 PM Thursday evening, mainly due to the forecast for sustained winds continuing into Thursday. Some gusts near 45-50 mph are also possible.

For late this week into this weekend, model guidance remains largely split into two camps. One camp allows the low to continue to track northeastward away from the region, and the other camp features a westward deviation of the low, or even additional surface cyclogenesis closer to the coast. Given these factors, uncertainty for Friday and beyond remains quite high, with a large range of potential outcomes. The deterministic EC and all of its ensembles continue to feature the scenario that would lead to greater impacts. The deterministic GFS remains far enough out to sea to keep impacts confined to the immediate coast with gusty winds and minimal rainfall. The 00Z deterministic GFS and EC runs were both slower in the low pressure strengthening and a bit farther east again, which does seem to be a more probable solution given upper level wind field evolution. Nevertheless, uncertainty for forecast details Friday and beyond remains high. With that said, regardless of the exact outcome, coastal flooding, marine and surf hazards are expected to continue through at least Saturday.

PoPs increased some in the eastern half of our area, and are now in the 20-60% range into the weekend. Regardless of which scenario pans out, precipitation chances and winds will be highest close to the coast and decrease with inland extent.

Sunday night into Monday, regardless of which scenario ultimately pans out, the low will begin to track away from the area, allowing rain chances to decrease and winds to subside.

KEY MESSAGE 3...Multiple rounds of significant tidal flooding expected for this week. Coastal Flood Warnings and Advisories are in effect.

With a slow moving coastal storm and multiple days of strong northeast winds expected, the confidence in the threat for tidal flooding remains high. Strong onshore flow that is projected to last for several days will result in water piling up across tidal tributaries and within back bays of coastal communities. Tidal levels will also be enhanced with astronomical tides increasing with the upcoming Full Moon on Saturday. This combination of factors will lead to widespread tidal flooding, some of which is expected to get to the Moderate stage. While not currently forecast, the threat for major flooding is not off the table, especially getting near the full moon. Tidal guidance diverges greatly beyond Thursday Night at nearly all of our forecast points. Some guidance has moderate to even major flooding for the weekend while some barely has tide levels getting into minor flood stage. It all will depend on the track of the coastal storm.

Most areas within the Coastal Flood Advisory saw widespread minor flooding on Tuesday, especially back bay communities. The forecast remains on track. The Coastal Flood Warnings and Advisories for Delaware and Salem County are already in effect. Coastal Flood Warnings and Advisories go into effect this afternoon for the NJ Atlantic coastline. These were extended in time to cover the high tides through Friday evening. While the exact severity of the coastal flooding on Friday remains less certain, tidal flooding is expected to continue through this time, and impacts could reach their greatest extent on Friday depending on how the storm evolves. Tidal flooding may continue through Saturday as well, but confidence is much lower by Saturday at this time and impacts are anticipated to be lessening by then.

For the tidal Delaware River, tide levels are expected to reach widespread minor today and Thursday. Coastal Flood Advisories remain in effect for the tidal Delaware River through Thursday night's high tide. As with the areas mentioned above, widespread minor tidal flooding may continue through Friday and into the weekend.

Usually, strong northeast winds do not result in tidal flooding along the upper Eastern Shore of Maryland. However, given the duration of surge in the lower/southern portion of the bay with widespread moderate to major flooding forecast there, it is becoming increasingly likely that portions of our Eastern Shore counties will experience some minor tidal flooding toward the end of the week. Our latest forecast includes Claiborne reaching minor flood stage for 4 consecutive high tides beginning with tonight's high tide. Thus, a Coastal Flood Advisory was issued for Queen Anne's Talbot, and Caroline Counties. Our latest forecast has also increased slightly for Tolchester Beach, and and expansion to Kent (MD) County may be considered in a future update depending on how surge values trend. By Friday and Saturday, winds shifting more northerly should help the bay to begin draining some.

KEY MESSAGE 4...Dangerous rip currents and high surf are expected at the Jersey Shore and Delaware Beaches through the end of the week. Significant beach erosion is also likely. Breaching of sand dunes is possible.

A coastal storm developing offshore will result in hazardous conditions along the coast. The surface low will linger off our coast for multiple days, bringing strong northeast winds and high seas for our marine zones. Breaking waves within the surf zone of 6 to 12 feet are expected beginning today through Saturday. Dangerous rip currents will accompany the high surf, making it extremely dangerous to enter the water at any time this week and into Saturday. The high surf and strong winds could also result in significant beach erosion and breaching of sand dunes for the Jersey Shore and Delaware Beaches.

With high confidence in the rip current and high surf forecast, the High Risk for life threatening rip currents is now in effect through Saturday for all beaches. A High Surf Advisory remains in effect for all beaches as well, which was extended in time through Saturday, when breaking waves within the surf zone will be around 6-12 feet.

AVIATION /12Z WEDNESDAY THROUGH SUNDAY/

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

Today...MVFR ceiling possible at MIV and ACY through 14Z. VFR ceilings elsewhere. Northeast winds increasing 15-20 kts with gusts 25-30 kts. Gusts up to 35 kts possible at ACY and near other coastal areas. High confidence.

Tonight...VFR conditions expected to prevail, though ceilings may lower to near MVFR at MIV/ACY late. Northeast winds 10-15 kts with gusts 20-25 kts. High confidence in prevailing conditions.

Outlook...

Thursday through Thursday night...Prevailing VFR conditions expected, but low clouds could lead to restrictions at times. Gusty northeast winds.

Friday through Sunday...Uncertainty remains high, but restrictions are possible at times in low clouds and rain. Gusty north winds.

MARINE

Northeast winds will strengthen with gale force gusts spreading across all coastal waters today, including Delaware Bay. Gale force winds/gusts are forecast to occur today through Thursday, peaking around 25-35 kts with gusts up to 45 kts possible. Dangerous seas building 8-15 feet. Winds will lessen for upper Delaware Bay on Thursday though. Gale Warnings remain in effect.

Visibility restrictions will be possible at times from sea spray.

Outlook...

Gale force winds are likely to persist Friday into Saturday across all coastal and offshore waters, and potentially Delaware Bay (lower confidence). There is potential for storm force wind gusts up to 50 kts for the offshore waters Thursday night through Saturday, and Storm Watch was issued to highlight this threat. Uncertainty remains high beyond Thursday night due to the uncertainty in how the storm offshore will evolve.

Visibility restrictions will be possible at times in rain and sea spray Friday through Sunday.

Rip Currents...see Key Message 4.

PHI WATCHES/WARNINGS/ADVISORIES

PA...Coastal Flood Advisory from 10 PM this evening to 4 AM EDT Friday for PAZ070-071-106. NJ...Coastal Flood Advisory until 1 AM EDT Saturday for NJZ016. High Risk for Rip Currents through Saturday evening for NJZ014- 024>026. High Surf Advisory until 6 PM EDT Saturday for NJZ024>026. Wind Advisory until 8 PM EDT Thursday for NJZ014-024>026. Coastal Flood Advisory from 4 PM this afternoon to 2 AM EDT Saturday for NJZ012>014-021. High Surf Advisory until 2 PM EDT Saturday for NJZ014. Coastal Flood Advisory from 10 PM this evening to 4 AM EDT Friday for NJZ017>019. Coastal Flood Warning from 4 PM this afternoon to 2 AM EDT Saturday for NJZ020-022>027. DE...Coastal Flood Advisory until 1 AM EDT Saturday for DEZ001. Coastal Flood Warning until 2 AM EDT Saturday for DEZ002>004. High Risk for Rip Currents through Saturday evening for DEZ004. High Surf Advisory until 6 PM EDT Saturday for DEZ004. Wind Advisory until 8 PM EDT Thursday for DEZ004. MD...Coastal Flood Advisory from 2 AM Thursday to 8 AM EDT Friday for MDZ015-019-020. MARINE...Gale Warning until 6 AM EDT Thursday for ANZ430. Gale Warning until 8 PM EDT Thursday for ANZ431. Gale Warning until 6 AM EDT Friday for ANZ450>455. Gale Warning until 6 PM EDT Thursday for ANZ480>483-485. Storm Watch from Thursday evening through Saturday afternoon for ANZ480>483-485.