textproduct: Philadelphia/Mt Holly

WHAT HAS CHANGED

Updated key messages as well as the aviation and marine sections.

KEY MESSAGES

1. Low pressure well off the Mid-Atlantic coast will move even farther away Thursday, however some coastal impacts and hazardous marine conditions continue.

2. Elevated tide cycles persist due to a storm off the coast with water levels peaking with this evening's high tide. Widespread minor coastal flooding is expected from Ocean County NJ southward through Delaware.

3. Frost impacts possible Friday night and Saturday night where the growing season continues.

DISCUSSION

KEY MESSAGE 1...Low pressure well off the Mid-Atlantic coast will move even farther away Thursday, however some coastal impacts and hazardous marine conditions continue.

Low pressure located well off the Mid-Atlantic coast will strengthen through tonight as it gradually turns more to the northeast. This northeast or east-northeast motion then continues on Thursday. Meanwhile, strong surface high pressure centered across New England will shift into the Canadian Maritimes tonight. A tightened pressure gradient remains between these two systems through tonight.

Some impacts remain only for our coastal and marine areas. The multi- day north-northeast wind has resulted in 10+ foot waves just offshore. These big waves breaking onto the beaches will result in some additional beach erosion especially during times of high tide. Peak wind gusts in the 30-40 mph range into this evening for areas along the coast, and 20-30 mph inland. The winds will diminish late this afternoon and especially tonight particularly away from the immediate coast. Some mid to mostly high clouds into tonight will occur especially closer to the coast. As the winds diminish tonight, it will be a chilly night, however frost is not expected.

For Thursday into Friday, the ocean storm will move farther out to sea as an incoming system from the northwest kicks it out. This will reduce the marine and coastal impacts, while keeping our weather dry and providing a fresh shot of chilly air. There will still be a notable north-northwest breeze Thursday as the pressure gradient remains tightened due to another incoming strong surface high from Canada.

KEY MESSAGE 2...Elevated tide cycles persist due to a storm off the coast with water levels peaking with this evening's high tide. Widespread minor coastal flooding is expected from Ocean County NJ southward through Delaware.

As a storm continues to linger off the coast, elevated tide cycles persist with water levels peaking this evening. Expect fairly widespread but minor flooding from Ocean County NJ southward through Delaware including the Delaware shores of Delaware Bay. In some of the back bays, moderate coastal flooding is still possible this evening however the chances for this have lowered some as recent tide cycles have generally not been quite as high as forecast. Beyond this evening, the storm will gradually be moving to the northeast away from the region for the end of the week. Another round of minor coastal flooding is possible Thursday evening though at this time it's looking to be more spotty in nature.

At this time we are not forecasting any coastal flooding for the Maryland eastern shore.

KEY MESSAGE 3...Frost impacts possible Friday night and Saturday night where the growing season continues.

As an upper-level trough pivots across the Northeast on Friday, a potentially strong mid level ridge in the Plains to Midwest shifts eastward some into the weekend. This will support strong surface high pressure initially centered near the Great Lakes and portions of eastern Canada, which then shifts eastward into the Northeast and Mid-Atlantic Friday and over the weekend.

A chilly and dry air mass will accompany this strong surface high, and as the high itself settles more overhead the winds will decouple. This will set the stage for efficient radiational cooling both Friday night and Saturday night. The forecast lows are in the 30s for much of the area (away from the coasts and outside of the urban centers) with a frost potential. It is possible that if the radiational cooling ends up being stronger, then some areas could get to freezing or a little below. Overall though, frost impacts are possible where the growing season remains active.

AVIATION /18Z WEDNESDAY THROUGH MONDAY/

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

Rest of this afternoon...VFR with some high clouds. North-northeast winds 10-15 knots with gusts 20-25 knots at times. Moderate confidence.

Tonight...VFR. North-northeast winds diminishing to 10 knots or less, then becoming north-northwest (becoming locally light and variable). Moderate confidence.

Thursday...VFR. North to northwest winds increasing to 10-15 knots with some gusts to around 20 knots. Moderate confidence.

Outlook...

Thursday night...VFR. North-northwest winds diminishing to 10 knots or less.

Friday through Monday...VFR.

MARINE

The wind field into our area has been less overall and the latest guidance overall continues to keep gales east of the New Jersey and Delaware Atlantic coastal waters. A Small Craft Advisory continues for the New Jersey and Delaware nearshore waters. The Small Craft Advisory for lower Delaware Bay goes through the day Thursday.

An area of strong low pressure well offshore will move even farther out to sea on Thursday. A tightened pressure gradient will remain in place however due to strong high pressure to our north. Gale Warnings continue for our offshore zones with a Small Craft Advisory elsewhere through Thursday. Seas 8-15 feet on the ocean, with 5-8 foot waves into portions of lower Delaware Bay (more likely closer to the mouth of the bay). The winds are forecast to weaken some tonight.

Outlook...

Friday...Small Craft Advisory conditions probable, mainly on the ocean zones due to lingering 5+ foot seas.

Saturday...Winds are forecast to be below Small Craft Advisory criteria, however seas around 5 feet may linger for a while longer especially for our southern Atlantic coastal waters.

Sunday and Monday...The conditions should be below Small Craft Advisory criteria..

PHI WATCHES/WARNINGS/ADVISORIES

PA...None. NJ...Coastal Flood Advisory from 6 PM to 10 PM EDT this evening for NJZ016. Coastal Flood Advisory until 10 PM EDT this evening for NJZ020- 022>027. DE...Coastal Flood Advisory from 6 PM to 10 PM EDT this evening for DEZ001. Coastal Flood Advisory until 10 PM EDT this evening for DEZ002>004. MD...None. MARINE...Small Craft Advisory until 6 PM EDT Thursday for ANZ431. Small Craft Advisory until 8 PM EDT Friday for ANZ450>455. Gale Warning until 6 AM EDT Thursday for ANZ480>483-485.