Philadelphia, PA 19192 Weather

What Has Changed

Updated Key Message 1 and added Key Message 3. Aviation and marine sections updated.

Key Messages

1. A well offshore nor'easter bringing coastal impacts and hazardous marine conditions through Thursday.

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

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

Discussion

KEY MESSAGE 1...A well offshore nor'easter bringing coastal impacts and hazardous marine conditions through Thursday.

A closed low off the Mid-Atlantic coast will gradually shift north and eastward through later this week. This will continue to support surface low pressure, which is forecast to strengthen as it slowly moves north and northeastward (even meanders some for a time). Meanwhile, strong surface high pressure will become more centered across northern New England through Wednesday. These systems will result in a tightening pressure gradient into our area through late Wednesday.

While this this nor'easter remains hundreds of miles off of our coast (an ocean storm), some impacts are still being felt for our coastal and marine areas. The wind field has strengthened some today with stronger surface winds being observed across most of the area. Some of this wind will decouple tonight, especially farther inland, but still remain breeze to windy at the coast. This continued north to north-northeast wind will build the offshore seas and these will be breaking into the beaches resulting in beach erosion in some areas especially during times of high tide. The pressure gradient should tend to tighten some more tonight and for portions of Wednesday as the storm is forecast to shift westward some or even make a small offshore loop on Wednesday. This should result in the winds peaking tonight and Wednesday. For areas along the coast, peak wind gusts in the 30-40 mph range are forecast and then up to 30 mph inland. No impacts are expected inland given how far offshore this storm is. Some showers may try and approach the immediate coast though during Wednesday, but overall the drier air on the west side of this system along with the offshore distance should keep these areas mainly dry. Some cloudiness should spread westward for a time Wednesday, however this may be mainly the mid to high level variety.

For Thursday and Friday, the storm will gradually head farther out to sea as an incoming system from the northwest kicks it out. This will quickly lessen the marine and coastal impacts, while keeping our weather dry and providing a fresh shot of chilly 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.

Rest of this afternoon...VFR. North-northeast winds 10-15 knots with gusts to 25 knots. Moderate confidence.

Tonight...VFR. North-northeast winds diminish to 10 knots or less for a time, then should increase with some gusts to 20 knots especially at KACY. Moderate confidence.

Wednesday...VFR. North-northeast winds 10-15 knots with gusts 20-30 knots, with the strongest winds mainly at KACY and KMIV. Gusts could be limited at KABE and KRDG. Moderate confidence.

Outlook...

Wednesday night and Thursday...VFR. North-northwest wind gusts to 20 knots possible on Thursday.