textproduct: Gray - Portland

WHAT HAS CHANGED

A frost advisory has been issued for parts of central New Hampshire and western Maine for tonight.

KEY MESSAGES

1. High pressure remains in control of the weather pattern through late in the week.

2. A coastal storm may bring soaking rain, gusty winds, and high surf from Friday through the upcoming weekend.

DISCUSSION

KEY MESSAGE 1 DESCRIPTION...

High pressure continues to build across northern New England over the next couple of days. This brings with it a seasonably cool airmass, as well as some chances for frost tonight and again Wednesday night. A frost advisory has been issued for a few zones that are still active through central New Hampshire and parts of western Maine. South of these areas, a northeasterly breeze overnight keeps any frost isolated and patchy. Tomorrow night looks cooler as the high pressure center peaks overhead, so more areas of frost will be possible tomorrow night as well. During the daytime, mainly sunny skies with highs in the 60s continue.

While the high brings cool and fair weather to northern New England, it also keeps a developing storm system off the Carolinas to our south. The surf will start to build on Wednesday as a long easterly fetch develops across the North Atlantic between the high overhead and the developing storm system. These waves will steadily build on Thursday and through the end of the week bringing increasingly large breaking surf and rip currents. Most land based impacts from the system hold off until at least this weekend.

KEY MESSAGE 2 DESCRIPTION...

Starting Friday...An area of low pressure offshore of the Mid- Atlantic is forecast to slowly lift northward and deepen Friday into the first part of the weekend before stalling out and meandering for at least the second half of the weekend. There's slightly more agreement within today's ensembles in the northward extent the low gets, but there continues to be a fair amount of spread in how far offshore it remains or if there is a drift back west before pulling away early next week. The majority of the GEFS/AIGFS ensemble members are favoring the low center closer to but still south or east of Cape Cod while the majority of the ECMWF camp favors the low a bit farther to the west...south of the southern New England coast. It should be noted that each of these models also has multiple members that support the other solution as well as some farther offshore, so a degree of certainty exists.

Of higher confidence/less uncertainty: either way, the pressure gradient will be tight across the region between the low and a high to the north and west. So gusty north to northeast winds are increasingly likely, especially along the coast. In addition to this, a long fetch of these winds and swell will build seas over the Gulf of Maine and bring the threat of high surf and a high risk of rip currents at area beaches. This will also coincide with a period of high astronomical tides, and given the increasing wind/wave forecast, coastal flooding will be another possibility surrounding the times of high tide.

Lesser confidence and more uncertainty is how much rain will fall, but there is potential for soaking rain, especially along the coast and portions of southern NH. NBM PoPs bring the higher (low end likely) PoPs along the coast and into southeast NH which is sufficient for the time being given the remaining spread in the guidance. Temperatures may also stay in the 50s if the rainier/cloudier scenario pans out.

The weekend conditions may carry into Monday, but ensembles favor the low pulling away to the east by Tuesday of next week.

AVIATION /18Z TUESDAY THROUGH SUNDAY/

VFR prevails during the daytime through Thursday, with nighttime valley fog possible at HIE and LEB each night.

Outlook...

Friday: Mainly VFR.

Friday night-Sunday...Low pressure over the western Atlantic could bring periods of MVFR ceilings and rain, especially along the coast and southern NH. Visibilities may drop to IFR at times. In addition, gusty north to northeast winds are possible.

MARINE

An easterly swell continues to build over the next few days while High pressure remains over the waters. SCA conditions gradually spread north over the next couple of days, with waves reaching 5ft starting across the southern waters by midday Wednesday, and then expanding northward through Thursday.

Friday-Tuesday...Strong low pressure over the western Atlantic and a high pressure to the north and west will result in a tight pressure gradient over the waters. Although there is uncertainty in where the low pressure center will be, increasing north to northeast winds will likely result in at least SCA conditions, but there's increasing chances in seeing periods of gales from Friday through the weekend and potentially into early next week. Highest chances for gales will be outside of the Bays and especially over the outer waters.

GYX WATCHES/WARNINGS/ADVISORIES

ME...Frost Advisory from midnight tonight to 7 AM EDT Wednesday for MEZ012-033. NH...Frost Advisory from midnight tonight to 7 AM EDT Wednesday for NHZ003-004. MARINE...Small Craft Advisory from 11 AM Wednesday to 8 PM EDT Thursday for ANZ154.