textproduct: Gray - Portland

WHAT HAS CHANGED

A Coastal Flood Watch has been issued for the New Hampshire Seacoast and Coastal York County where surge is expected to be maximized by the mostly onshore winds.

KEY MESSAGES

1. A strong nor'easter will loop south of New England this weekend. A prolonged period of soaking rain, gusty winds, high surf, and coastal flooding are likely into early next week.

2. High pressure keeps fair weather is place through today, with rain showers arriving across southern zones tonight. Deteriorating marine and surf conditions later today and tonight as northeast winds increase.

DISCUSSION

KEY MESSAGE 1 DESCRIPTION...

Model guidance is finally starting to hone in on some sort of agreement on the general nor'easter evolution. Very similar tracks and clusters are noted across GEFS, ECMWF Ens, and GEPS. The loop is now occurring closer to Long Island and thus the local impacts are somewhat capped by distance. However there really is not much change in the messaging that is necessary. We still expect the same impacts and similar timing, it is the magnitude that is becoming a little more clear.

High surf: Available guidance is in solid agreement with seas peaking around 15 ft in the vicinity of Jeffrey's Ledge during the day Sat. Given the long duration northeast winds and favorable long fetch plus wind gusts perhaps approaching storm force I could see those significant wave heights reaching 18 ft or so. High Surf Advisory remains in effect for both large, breaking nearshore waves and high rip current risk. Those wave heights will likely remain at or above 10 ft into Sun.

Coastal flooding: A common theme of some of notable coastal flooding events has been prolonged surge over several tide cycles due to either slow or stalled storms. This one fits the bill for one that should be able to drive surge up to around 2 ft. Guidance is a little lower than that, so we may need to bump the surge forecasts up in the coming 24 hours. The track is actually a close match for the March 2018 nor'easter which brought several days of coastal flooding. Now the difference is that storm was much stronger and astronomical tides were about a foot higher than those this weekend. The coastal flood forecast matrix for the beaches south of Portland puts us right on the edge of Advisory and Warning. A Coastal Flood Watch has been issued for those areas given that we are on edge and preparations will need to be underway soon if action needs to be taken.

Winds: Guidance is now providing some good confidence that the strongest winds will be Sat into Sat night. This is when the northeast LLJ is forecast to be the strongest, but we cannot quite match the magnitude forecast over southern New England. I have fairly high confidence that a 48+ hour period of greater than 30 kt gusts is likely. There is a window late Sat into Sun when we may mix down some slightly higher gusts. Either way leafed trees stressed by drought conditions and soaking rainfall may combine to make tree damage a little more likely than usual. I still think a Wind Advisory is possible for portions of southwestern Maine and southeastern NH. We still have some lead time on that, but will likely need to make a decision by this afternoon.

Rainfall: This remains the lowest confidence impact of the bunch. Despite the growing confidence in track, guidance is still has a fair bit of spread on rainfall amounts and locations of the heaviest QPF. There has been a trend to slow down the rainfall into the local area, with guidance not bringing a high likelihood of the first measurable precip until late Sat in some cases. In addition the probability of 4 inches or more QPF has come down to 10 percent or less. Only the ECMWF Ens now has any threat of 2 inches QPF in 24 hrs, and that has shifted into late Sun into Mon. So overall I do not anticipate flooding to be a concern from rainfall alone - there could be some drainage issues around high tides in the low lying areas. The best chances for 1 to 2 inches of rain will be southern NH into southwestern Maine, and the soaking rainfall is most likely south of the mtns. The biggest change with this forecast cycle is likely going to be extending the chances of rain thru Mon for most locations.

KEY MESSAGE 2 DESCRIPTION...

Strong high pressure and very dry air across northern New England will keep conditions dry through today. Moisture does begin to increase tonight with some showers possible, mainly across southern zones.

Northeast winds will pick up today with gusts around 20-25 mph and perhaps 25-35 mph closer to the seacoast.

Friday will also see deteriorating marine and surf conditions that will remain dangerous and all the way through the weekend.

AVIATION /07Z FRIDAY THROUGH TUESDAY/

Through Tonight...Mainly VFR, except IFR or lower valley fog is likely again tonight at LEB and HIE. Northeast winds increase today, potentially gusting to 20-25 kt along the coast and 15-20 kt inland. VFR continues tonight despite some showers developing across southern terminals.

Outlook:

Saturday: Areas of MVFR developing as rain moves into the area. Northeast surface gusts of 30 kt or more possible near the coast.

Sunday: Widespread MVFR likely, areas of IFR or lower possible near the coast in rain. Coastal terminals may see northeast surface gusts of 35 kt or more, especially towards PSM.

Monday: Areas of MVFR or lower during the first half of the day as rain winds down. North northeast surface gusts of 25 kt or more possible.

Tuesday: Conditions becoming VFR expected.

MARINE

Conditions deteriorate today and tonight as the pressure gradient tightens as the nor'easter approaches southern New England from the south.

Northeast winds are expected to peak during the day Sat, perhaps lingering into Sat night before very slowly diminishing. Gale Warnings remain in effect for all waters outside of the bays, but it remains possible that for a time during the second half of Sat that gale force gusts are possible in the bays too, and storm force gusts are possible for the waters south of Cape Elizabeth. At least some SCA conditions likely linger into Mon night before subsiding. During the day Sat seas near Jeffrey's Ledge are likely to be pushing 15 ft, but persistent wind direction and long fetch may allow those to creep to near 18 ft. Moderate to locally heavy rainfall over the waters will also reduce visibility to below 3 miles at times thru Mon morning.

GYX WATCHES/WARNINGS/ADVISORIES

ME...High Surf Advisory from 8 AM Friday to 8 PM EDT Sunday for MEZ023>027. Coastal Flood Watch from Saturday morning through Sunday afternoon for MEZ023. NH...High Surf Advisory from 8 AM Friday to 8 PM EDT Sunday for NHZ014. Coastal Flood Watch from Saturday morning through Sunday afternoon for NHZ014. MARINE...Small Craft Advisory until 8 AM EDT Friday for ANZ150-152>154. Gale Warning from 2 AM Saturday to 8 PM EDT Sunday for ANZ150- 152. Small Craft Advisory from 8 AM Friday to 8 PM EDT Sunday for ANZ151-153. Gale Warning from 8 PM Friday to 8 PM EDT Sunday for ANZ154. Gale Warning from 11 AM Friday to 8 PM EDT Sunday for ANZ180- 182-184.