Cape Henlopen to Fenwick Island DE out 20 nm Marine Forecast
|Tonight...S Winds Around 5 Kt. Seas 2 Ft Or Less. A Chance Of Tstms This Evening, Then Showers Likely With A Chance Of Tstms After Midnight. Patchy Fog Late This Evening And Overnight With Vsby 1 To 3 Nm. Swell Mainly From The Se With A Dominant Period Of 8 Seconds.|
|Fri...Se Winds Around 5 Kt. Seas 2 Ft Or Less. Patchy Fog Until Late Afternoon. Showers Likely In The Morning. A Chance Of Tstms. A Chance Of Showers Early In The Afternoon. Vsby 1 To 3 Nm Until Late Afternoon. Swell Mainly From The Se With A Dominant Period Of 8 Seconds.|
|Fri Night...Se Winds Around 5 Kt, Becoming Ne After Midnight, Then Becoming Nw Late. Seas Around 3 Ft. Tstms Likely Until Early Morning, Then A Chance Of Tstms Late. Swell Mainly From The Se With A Dominant Period Of 6 Seconds.|
|Sat...Ne Winds Around 5 Kt. Seas 2 Ft Or Less. A Chance Of Tstms Early In The Morning. Swell Mainly From The Se With A Dominant Period Of 7 Seconds.|
|Sat Night...Se Winds Around 5 Kt, Becoming Sw After Midnight. Seas 2 Ft Or Less.|
|Sun...N Winds Around 5 Kt, Becoming Se In The Afternoon. Seas 2 Ft Or Less.|
|Sun Night...Sw Winds 5 To 10 Kt. Seas 2 Ft Or Less.|
|Mon...S Winds 5 To 10 Kt. Seas 2 Ft Or Less.|
|Mon Night...S Winds Around 10 Kt. Seas 2 Ft Or Less.|
|Tue...S Winds 10 To 15 Kt. Seas 2 Ft Or Less.|
|Tue Night...S Winds 10 To 15 Kt, Becoming Sw 5 To 10 Kt After Midnight. Seas Around 3 Ft. A Chance Of Tstms. Winds And Seas Higher In And Near Tstms.|
Area Forecast Discussion|
National Weather Service Mount Holly NJ
402pm EDT Thu August 6 2020
A weak stationary front will straddle the area through Friday, as an area of low pressure moves northeastward along it from Virginia today to near Cape Cod by Saturday morning. High pressure will build over New England this weekend into early next week. A cold front will approach the region slowly around the middle to end of next week.
Near Term - Until 6am Friday Morning
Frontal boundary remains draped over the area, generally extending from southern New Jersey down through Delmarva and into the Mid- Atlantic. Surface high pressure is building in from the Great Lakes and Ohio Valley, while the base of an H5 trough with strong shortwave energy lies over the Tennessee and Ohio Valleys.
Onshore flow in place, and this results in a tropical airmass with surface dewpoints well in the 60s and low 70s.
Low pressure will develop near the Mid-Atlantic as that trough approaches and interacts with the stalled boundary. PWATs (Precipitable Waters) fairly high, generally 1.5 inches down to the Fall Line, and as much as 2 inches in Delmarva. Going through the overnight, PWATs (Precipitable Waters) will creep up to 2 inches across northern zones and as high as 2.25 inches in southern zones.
Showers and thunderstorms currently developing across portions of Virginia and southern Maryland, just south of Delaware and the southeast Maryland shores. Although some storms may encroach on southern Delaware, the bulk should remain just south.
Conditions should mainly be dry into this evening, and then activity ramps up after midnight and towards the pre-dawn hours. Heavy rain likely, and antecedent conditions quite wet from Tropical Storm Isaias and other rain events, it will not take much rain to result in flash flooding.
Max Quantitative Precipitation Forecast seems to be a bit farther north than models previously indicated. Flash Flood Watch has been expanded one tier of counties north, and will extend it through midday Friday.
Short Term - 6am Friday Morning Through Friday Night
Rainfall intensifies over northern areas Friday morning, and 1-2 inches of Quantitative Precipitation Forecast are possible during through Friday morning. Flash Flood Watch extended into midday Friday.
A lull in showers, or at least the heaviest showers, is possible Friday afternoon, but as that aforementioned trough axis digs east, another round of showers and thunderstorms will develop late in the afternoon.
Once again, heavy rain is the primary threat.
Easterly flow remains in place, and with abundant cloud cover and rainfall, highs on Friday will remain in the 70s to low 80s.
Long Term - Saturday Through Thursday
A closed low that interacted with Tropical Storm Isaias will finally exit the Canadian Maritimes early Friday morning, leaving behind fragmented energy in the form of a shortwave trough over the Hudson Bay area. As the mid-level trough progresses east across the region Saturday, height falls around 20 m will combine with PWATs (Precipitable Waters) near 1.8” (between the 75th and 90th percentile for this time of year) to yield high chances of precipitation Friday night into Saturday afternoon. Once the system moves out of the region late Saturday night, subsidence behind the trough will bring in drier air with PWATs (Precipitable Waters) falling to around 1.20”. Low temperatures Sunday morning will be in the upper 60s, or relatively cool compared to previous nights, but near normal for this time of year. Weak high pressure will center over central PA with high temperatures in the mid to upper 80s. Dry weather is expected as PWATs (Precipitable Waters) remain around 1.20”.
Mid-level heigheights will begin to rise on Monday in advance of the next upper level low with low level flow turning from the southwest. As this occurs, the residual air mass from the previous week will quickly surge north with PWATs (Precipitable Waters) rising to around 1.40”. There is uncertainty on how quickly the Delaware Valley will transition to the moisture rich air, but the overall thinking is sometime in the afternoon hours. Due to this, showers and thunderstorms are expected across the region Monday afternoon. The upper level low will then move eastwards across Manitoba. On Tuesday, a mid-level disturbance will approach the area from the west. The GFS and European are agreeing well with the positioning of this disturbance. The best chance of precipitation with this disturbance appears to be Tuesday evening through Wednesday morning.
Wednesday afternoon, the wave will be exiting the region with a rather zonal flow setting up over the Delaware Valley. There is, again, uncertainty with the following upper level low that is expected to be near the Hudson Bay. The GFS has a higher amplitude low, while the European shows the low going more northward and being less amplified. The GFS is quicker with the front and brings it further south (central PA by Friday), while the European keeps the front well north of the region. For now, we have kept POPs close to climatology with a daily chance of showers and thunderstorms.
Tonight through Friday...Overall, sub-Small Craft Advisory conditions will be in place with SE to E flow 10 kt or less and 2-3 ft seas. However, several rounds of showers and thunderstorms will result in locally higher winds and seas, as well as reduced VSBY in heavy rain..
Outlook... Friday night into Saturday... Showers and thunderstorms appear likely with sub-SCA (Small Craft Advisory) winds and seas expected.
Saturday night through Tuesday...Sub-advisory winds/seas expected through the period. Cannot rule out a stray shower or storm during the afternoon/evening hours, but chances appear rather low overall.
Rip Currents... Seas continue to subside in the wake of Isaias. A low risk for the formation of dangerous rip currents is expected through Friday.
The NOAA Weather Radio All-Hazards broadcast from Hibernia Park Pennsylvania (Station WNG-704) remains off the air.
NOAA Mount Holly NJ Office: Watches - Warnings - Advisories
PA...Flash Flood Watch through Friday afternoon for PAZ060-070-071- 101>106. NJ...Flash Flood Watch through Friday afternoon for NJZ009-010- 012>027. DE...Flash Flood Watch through Friday afternoon for DEZ001>004. MD...Flash Flood Watch through Friday afternoon for MDZ008-012-015- 019-020. MARINE...None.