Philadelphia, PA 19101 Weather

What Has Changed

Updated key messages and marine section.

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 today will gradually shift north and eastward later this week. This is supporting surface low pressure, which is forecast to strengthen 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 Wednesday. 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 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, most likely Wednesday into Wednesday night. 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 northwest picks it up. This will quickly lessen the marine and coastal impacts, while keeping our weather dry and providing a fresh shot of cooler autumn air.

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 meanders offshore through the middle of the week, there will be a persistent and strong north-northeast wind in place. This will lead to a prolonged period of onshore flow resulting in multiple elevated high tide cycles. Recent forecast trends have been fluctuating on the crests of the high tide cycles for this event.

Aviation

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

Thru 12Z this morning...VFR. North winds around 3-8 kt becoming light and variable at times in a few spots. High confidence.

Today...VFR. North-northeast winds around 10-15 kt. Wind gusts up to 20 kt possible for I-95 terminals and up to 25 kt possible near MIV and ACY. Moderate-high confidence.

Tonight...VFR. North-northeast winds 5-10 kts, gusts may continue thru the night at ACY. Moderate-high confidence.

Outlook...

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