textproduct: Philadelphia/Mt Holly

WHAT HAS CHANGED

Aviation, marine sections and Key Message 1 updated.

KEY MESSAGES

1. A nor'easter well off the Mid-Atlantic coast will bring coastal impacts and hazardous marine conditions through about Thursday.

2. A prolonged period of onshore flow will lead to multiple elevated high tide cycles this week resulting in rounds of coastal flooding.

DISCUSSION

KEY MESSAGE 1...A nor'easter well off the Mid-Atlantic coast will bring coastal impacts and hazardous marine conditions through about Thursday.

A closed low off the southern Mid-Atlantic coast through Tuesday will gradually shift north and eastward later this week. This is supporting surface low pressure, which is forecast to strength as it slowly moves north and northeastward (even meander some for a time). Meanwhile, strong surface high pressure from the upper Ohio Valley to just off the New England coast will become more centered offshore of Maine by midweek. These systems will result in a tightening pressure gradient into our area through about late Wednesday.

This nor'easter, while remaining well offshore, will still result in some impacts for our area, mainly the coastal and marine areas. A prolonged period of strengthening north-northeast winds will push water toward/into the coast. Multiple rounds of coastal flooding are likely (see key message 2 below). Increasing seas will result in beach erosion in some areas, especially during times of high tide. For areas along the coast, wind gusts to about 35 mph are anticipated. Inland, no impacts are anticipated given how far offshore the storm is likely to be. No showers are currently expected even at the coast, given the distance this storm is forecast to be off the coast. This keeps the western extent of the deeper moisture and forcing also well east of our coastlines. Some stratocumulus however within the north- northeast flow will get into the coastal areas at times, especially from the central Jersey Shore to the Delaware Beaches. The closest approach to our coast for this storm looks to be during Wednesday. This should be the peak of the winds across the marine areas and along the coast.

For Thursday and Friday, the storm will gradually head farther out to sea as an incoming system from the west picks it up. This will quickly lessen the marine and coastal impacts.

KEY MESSAGE 2...A prolonged period of onshore flow will lead to multiple elevated high tide cycles this week resulting in rounds of coastal flooding.

As the nor'easter develops and meanders offshore through at least the middle of the week, there will be a persistent and strong northeast wind in place. This will lead to a prolonged period of onshore flow resulting in multiple elevated high tide cycles. The first high tide cycle of concern is currently expected to be Tuesday evening as spotty minor to minor tidal flooding is forecast. A Coastal Flood Advisory remains in effect for the Tuesday evening high tide cycle for Ocean, southeastern Burlington, Atlantic, Cape May, Kent, and Sussex County Delaware. This Advisory goes from 3 PM to 9 PM Tuesday and is for widespread minor coastal flooding.

The high tide cycle late Tuesday night into early Wednesday morning, looks to bring another round of spotty minor to widespread minor tidal flooding. An additional Coastal Flood Advisory will likely be needed for Ocean, southeastern Burlington, Atlantic, Cape May, Kent, and Sussex County Delaware.

Additional coastal flood hazards will likely be needed for high tide cycles Wednesday, and potentially Thursday, as the high tide cycles remain elevated. From the current forecast, Wednesday evening's high tide cycle looks to be the one of most concern with widespread minor to low-end moderate coastal flooding. Beyond Wednesday evening, another round of coastal flooding is possible but uncertainty remains in the exact extent as it will be dependent on the location of the nor'easter.

AVIATION /18Z MONDAY THROUGH SATURDAY/

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

Rest of this afternoon...VFR. North-northeast winds 8-14 knots (near 5 knots at KRDG/KABE). Some gusts 20-25 knots mainly at KMIV/KACY. High confidence.

Tonight...VFR. Northerly winds 5-10 knots, becoming light and variable mainly at KABE, KRDG and KTTN. Moderate confidence.

Tuesday...VFR. North-northeast winds increasing to 10-15 knots. Wind gusts 20-25 knots from the I-95 terminals on eastward from about 14z- 23z. Moderate confidence.

Outlook...

Tuesday night through Thursday...Primarily VFR. Gusty north-northeast winds at times.

Friday and Saturday...VFR.

MARINE

The pressure gradient between strengthening low pressure off the southern Mid-Atlantic coast and strong high pressure over New England will tighten tonight and especially Tuesday. The wind increase has been slower than forecast so far today and therefore did temper the increase a bit more into tonight. The overall wind field with the well offshore low looks to not be as strong to its far northwest extent. Maintained the Gale Warning for all Atlantic coastal waters and adjacent offshore zones, however cancelled the Gale Watch for the far northern New Jersey coastal water zone (Small Craft Advisory now covers this zone throughout the event). Small Craft Advisory conditions look to develop on Delaware Bay through Tuesday. Seas will also build in response to the increasing north- northeast winds.

Outlook...

Tuesday night through Thursday...A period of gales for much of the ocean water zones, with Small Craft Advisory conditions on Delaware Bay. It appears that the gale potential for lower Delaware Bay has diminished even more. Peak wind gusts in the Gale Warning are forecast to be between 35-45 knots. Seas build to 8-12 feet, lower on Delaware Bay. The winds and seas subside during the day Thursday.

Thursday night and Friday...Small Craft Advisory conditions probable.

Saturday...Winds are forecast to be below Small Craft Advisory criteria, however seas 5-7 feet may linger for a while longer for portions of the New Jersey/Delaware Atlantic coastal waters.

PHI WATCHES/WARNINGS/ADVISORIES

PA...None. NJ...Coastal Flood Advisory from 3 PM to 9 PM EDT Tuesday for NJZ020-022>027. DE...Coastal Flood Advisory from 3 PM to 9 PM EDT Tuesday for DEZ002>004. MD...None. MARINE...Small Craft Advisory until noon EDT Wednesday for ANZ430-431. Small Craft Advisory until 6 PM EDT Wednesday for ANZ450. Gale Warning until 6 PM EDT Wednesday for ANZ451>455. Gale Warning from 1 AM Tuesday to 6 PM EDT Wednesday for ANZ480. Gale Warning until 6 AM EDT Thursday for ANZ481>483-485.