textproduct: Philadelphia/Mt Holly

WHAT HAS CHANGED

Updated aviation discussion for 00z TAFs.

KEY MESSAGES

1. A high risk of rip currents and cold ocean water temperatures will create dangerous conditions tomorrow at the New Jersey and Delaware coasts.

2. Times of much needed rainfall through most of the holiday weekend and significantly cooler temperatures continuing, then some warming to end the holiday weekend.

DISCUSSION

KEY MESSAGE 1...A high risk of rip currents and cold ocean water temperatures will create dangerous conditions tomorrow at the New Jersey and Delaware coasts.

For tomorrow, an increasing east-northeast wind will range from 15 to 20 mph with 25 to 30 mph gusts. Seas will be increasing to 4-6 feet through the day. There will be a southeast swell with a period of 10 to 13 seconds and breaking waves of 2 to 4 feet. As a result, there is a HIGH risk for the development of dangerous rip currents on Friday and a Rip Current Risk Statement has been issued for all of the New Jersey and Delaware coasts.

Ocean temperatures continue to remain mainly in the 50s to low 60s. These cold water temperatures can quickly cause hypothermia and physical incapacitation to anyone suddenly immersed in the water.

KEY MESSAGE 2...Times of much needed rainfall through most of the holiday weekend and significantly cooler temperatures continuing, then some warming to end the holiday weekend.

A front will continue to settle to our south through Friday before trying to lift back northward over the weekend. Southwesterly flow aloft will guide ripples of energy and associated lift across our area and this will result in a zone of showers/rain early this evening that will continue to settle east/southward while also generally weakening. By the overnight period there will likely still be some light rain ongoing over portions of Delmarva and southern NJ but from around Philly northward it should be mainly dry.

Some mid level ridging slides over our area during Friday and this will result in surface high pressure building to our north across New England. This surface high will remain in place though Saturday and wedge its way down into the northern Mid-Atlantic. As this occurs, additional energy tracking up the Ohio Valley will support surface low pressure. As this low nears the eastern Great Lakes later Saturday, low-level warm air advection will increase above a marine layer across our region. This marine layer will be enhanced by the cool northeast to east low-level flow and create/maintain cool air damming. This is a very favorable setup for an overrunning event. The guidance is in good agreement that showers fill in by later Friday across the southern zones and then spread northward Friday night into Saturday, with a more steady rain evolving Saturday and Saturday night before tapering off Sunday. While the precipitable water values will be up to about 1.5 inches, this will be within a more stable low to mid level environment. Some heavier embedded rain is possible however the risk of thunder looks very low. This will also result in a rather chilly Saturday with a noticeable onshore breeze. The system them departs on Sunday with rain/showers ending overall, and temperatures should warm some however still be below average.

The pattern looks to remain active early next week, with some showers around on Memorial Day. It does look warmer for Memorial Day, but to what extent will depend on cloud cover and shower chances. While not great timing for the holiday weekend, our region needs more rain as a long-term drought continues. Rainfall totals through Friday night are mostly in the 0.10-0.50 inch range, and then 1-2 inches Saturday into Sunday.

AVIATION /00Z FRIDAY THROUGH TUESDAY/

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

Tonight...VFR to times of MVFR ceilings mainly during this evening for area south of RDG and ABE. East- northeast winds 5-8 knots, becoming locally light and variable. Low confidence.

Friday...Ceilings varying between MVFR and VFR. Some showers start to arrive from the south later in the day. East-northeast winds 10-15 knots, with some gusts 15-25 knots. Low confidence.

Outlook...

Friday night through Saturday night...MVFR/IFR conditions with rain.

Sunday...MVFR/IFR conditions with some rain ending, however conditions should then improve some.

Monday and Tuesday...Mostly VFR. Some showers still possible.

MARINE

A northeast flow will increase into tonight with gusts to 20 knots, then diminish some tonight before increasing again Friday morning. Seas will build through late Friday. The Small Craft Advisory has been delayed until early this evening for the ocean zones (except no advisory for the waters off Monmouth County and the upper Delaware Bay through tonight). The Small Craft Advisory continues Friday, with the upper Delaware Bay then included.

Outlook...

Friday night through Monday... Small Craft Advisory conditions probable.

Tuesday...Winds are anticipated to be much lighter, however seas may still be around 5 feet for a time.

Rip Currents...

For Friday, east-northeast winds will range from 15 to 20 mph with 25 to 30 mph gusts. There will be a southeast swell with a period of 10 to 13 seconds and breaking waves of 2 to 4 feet. As a result, there is a HIGH risk for the development of dangerous rip currents on Friday and a Rip Current Risk Statement has been issued for all of the New Jersey and Delaware coasts.

On Saturday, winds are more out of the east and will range from 20 to 25 mph with 30 to 35 mph gusts. Seas will reach 6-8 feet with a period of 10 to 13 seconds and breaking waves of 2 to 4 feet. This should result in a HIGH risk for the development of dangerous rip currents.

Ocean temperatures continue to remain mainly in the 50s to low 60s. These cold water temperatures can quickly cause hypothermia and physical incapacitation to anyone suddenly immersed in the water.

For specific beach forecasts, visit weather.gov/beach/phi

PHI WATCHES/WARNINGS/ADVISORIES

PA...None. NJ...High Risk for Rip Currents from Friday morning through Friday evening for NJZ014-024>026. DE...High Risk for Rip Currents from Friday morning through Friday evening for DEZ004. MD...None. MARINE...Small Craft Advisory from 6 AM Friday to 6 AM EDT Saturday for ANZ430. Small Craft Advisory until 6 AM EDT Saturday for ANZ431- 451>455.