Philadelphia, PA 19099 Weather

What Has Changed

Updated Aviation section for 12Z TAFs.

Key Messages

1. A nor'easter well off the coast will bring 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, with the peak being this evening.

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

Discussion

KEY MESSAGE 1...A nor'easter well off the coast will bring 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 be centered across northern New England today. These systems will result in a tightening pressure gradient into our area through this evening.

While 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 continued north to north- northeast wind has built 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 today as the storm is forecast to shift westward some or even make a small offshore loop today. This should result in the winds peaking today. 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 the day, 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 later today into tonight, 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, with the peak being this evening.

As the nor'easter meanders offshore through the middle of the week, there is a persistent and strong north-northeast wind in place. This prolonged period of onshore flow will result in multiple elevated high tide cycles. Recent forecast trends have been lowering 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.

Today...VFR with some high clouds, especially near KMIV and KACY. North-northeast winds around 10 kt with gusts up to 20 kt; highest near KACY and KMIV. Gusts could be limited at KABE and KRDG. Moderate-high confidence overall.

Tonight...VFR. Winds north-northeast dropping back to 5-10 kts most sites, a bit stronger ACY. Moderate-high confidence.

Outlook...

Thursday...VFR. North-northwest wind gusts to 20 knots possible.

Friday through Sunday...VFR.