textproduct: Gray - Portland

WHAT HAS CHANGED

No major changes needed early this morning. A band of very light showers moved through overnight, but dry air continues to fight back and keep the better rain chances at bay until later this afternoon or even early evening. The Aviation Discussion has been updated for the 12Z TAFs.

KEY MESSAGES

1. Dangerous marine condition continue through the weekend with large breaking waves and a high risk of rip currents. Splash- over and minor coastal flooding are possible for several high tide cycles beginning this morning through late Sunday evening.

2. This nor'easter will also lead to areas of widespread beneficial rain south of the mountains and gusty northeast winds through at least Monday along the coast and southern New Hampshire. It will turn drier and warmer once the storm moves away from the region.

DISCUSSION

KEY MESSAGE 1 DESCRIPTION...

A well developed nor'easter continues to slowly retrograde off the Mid Atlantic coast, with winds south of southern New England already pushing storm force. The big trend today has been for models to remain farther southwest than previous runs. Overall this does little to reduce the marine impacts from this system, hence why this section is broken out on its own.

Persistent northeast winds have already built seas to a consistent 8 to 12 feet from the central Maine shelf buoy southward. Combined with periods over 10 seconds and it is an ideal situation for dangerous nearshore breaking waves and rip currents. The High Surf Advisory remains in effect thru Sun. Seas look to peak sometime late this afternoon or during the evening, somewhere around 15 to 17 ft near Jeffrey's Ledge.

Building seas and steady northeast wind direction will also be ideal for generating a large storm surge. It is already sitting at 0.75 to 1 ft with plenty of time left to build that thru Sat. Our surge forecasts are a little higher than that, so I will nudge that down slightly until this afternoon. Overall tides are not their highest of the month, but rising. Given that we need at least 2 ft of surge to see flooding at most locations I think this will be a primarily splash-over event. That being said the usual vulnerable locations may see minor flooding, and the fact that this occurs over several tide cycles and the dunes may get worn down could mean later tides Sun and Mon have a better chance at those inundation issues in the trouble spots. The Coastal Flood Advisory also remains in effect thru Sun.

KEY MESSAGE 2 DESCRIPTION...

The biggest change the shift southwestward has caused is reducing the impact of both winds and rainfall across the local area.

I still expect an extended period (> 48 hours) of wind gusts along the coast and parts of southern NH greater at or above 35 mph. With the core of the northeast LLJ shifted so far south now, it is hard to really see much support for widespread 45+ mph gusts. That is mostly confined to a narrow window this afternoon or evening in the vicinity of the Seacoast. Otherwise forecast soundings show consistent mixing height tapping the bottom of the LLJ around 35 kt. The NBM does taper off overnight, so my preference is to increase those overnight winds but during the day looks fine. HRRR guidance looks pretty good in that respect, so I will blend that in to the NBM guidance. Still with leaves left on trees there is a limited power outage threat from falling limbs.

Rainfall may be what takes the biggest hit from the shift south. Steady rainfall may not make it into most of the forecast area until late this afternoon or early this evening. So the NBM PoP may have to get delayed a bit again. There is also a noted transition towards more showery or waves of showers as the low pressure fills and forcing becomes less intense. Ensemble system have all but taken the extreme rainfall scenarios off the table. There are just a handful of members producing amounts over 4 inches now. The highest probabilities for a good soaking rain (around 1 inch or more) will be south of the mtns, with the greater than 50 percent chance of 2 inches or more confined to the area from Portland to the Lakes Region southwestward into the Monadnocks. The southwest shift also means that it will take longer to clear the region as it moves back northeast eventually, so the likely PoP and greater has been extended further into Mon and Mon night.

Warmer and drier weather is expected mid to late week with temperatures a good 5 to 10 degrees above normal.

AVIATION /12Z SATURDAY THROUGH WEDNESDAY/

Through 12Z Sunday...VFR prevails through morning, but ceilings will be lowering as the day goes on and rain approaches the region. Coastal terminals likely fall to MVFR by late in the afternoon with inland terminals barely holding on to VFR. Brief IFR restrictions are possible if heavy rain moves over a terminal. North-northeasterly wind gusts will generally be 20-25kts today with 30 kts possible at coastal terminals.

Outlook:

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 in rain/showers. North northeast surface gusts of 25 kt or more possible.

Tuesday: Conditions improving to VFR. A few showers may linger over the mountains.

Wednesday: VFR expected.

MARINE

Developing nor'easter continues to build winds and seas over the coastal waters. The worst of the marine conditions are expected today thru tonight. Gale Warning remain in effect for all waters but the bays, with a strong SCA in the bays. Those conditions will last thru Sun before things begin to diminish. SCA conditions will linger into Mon evening before dropping below thresholds. High pressure brings further improvement in winds and seas toward midweek before a front approaches from the west late next week.

GYX WATCHES/WARNINGS/ADVISORIES

ME...High Surf Advisory until 8 PM EDT Sunday for MEZ023>027. Coastal Flood Advisory from 10 AM this morning to 11 PM EDT Sunday for MEZ023. NH...High Surf Advisory until 8 PM EDT Sunday for NHZ014. Coastal Flood Advisory from 10 AM this morning to 11 PM EDT Sunday for NHZ014. MARINE...Gale Warning from 11 AM this morning to 8 PM EDT Sunday for ANZ150-152. Small Craft Advisory until 8 AM EDT Monday for ANZ151-153. Gale Warning until 8 PM EDT Sunday for ANZ154-180-182-184.