textproduct: Boston / Norton

WHAT HAS CHANGED

There have been no significant changes to the expected track of the offshore nor'easter. However, uncertainty remains in rainfall amounts across the Cape and Islands due to the potential for a narrow band of enhanced precipitation. Gale Warnings have been extended through Thursday evening across the ocean waters, and a Gale Watch has been issued for the northeastern coastal waters from Thursday evening into early Friday afternoon as the nor'easter tracks northeast.

KEY MESSAGES

- A slow-moving nor'easter remains offshore through Thursday. Most of southern New England stays dry, but locally heavier rainfall is possible across the Cape and Islands. Gusty northeast winds and dangerous marine conditions remain the primary concerns.

- Fairly cool on Friday with a very low chance of an early morning shower. Otherwise, moderating temperatures and dry conditions are expected for the weekend into early next week.

DISCUSSION

KEY MESSAGE 1...A slow-moving nor'easter remains offshore through Thursday. Most of southern New England stays dry, but locally heavier rainfall is possible across the Cape and Islands. Gusty northeast winds and dangerous marine conditions remain the primary concerns.

There have been no significant changes to the overall track of the nor'easter, which remains several hundred miles south-southeast of southern New England. The system continues to meander over the warm waters of the Gulf Stream and is expected to make little progress over the next 12 to 18 hours before eventually tracking northeast and out to sea. As previously discussed, the National Hurricane Center continues to monitor this system for potential subtropical development, with the latest outlook indicating a 40 percent chance of development over the next seven days. However, the low remains associated with frontal boundaries. Even if the system were to acquire subtropical characteristics and receive a name, no meaningful changes to the expected impacts across southern New England are anticipated.

Meanwhile, gusty northeast winds continue to be one of the more noticeable impacts from this offshore nor'easter. The pressure gradient between strong high pressure to our north and the nearly stationary low pressure system offshore will maintain breezy to gusty conditions through today. The strongest winds will remain focused along the eastern Massachusetts coastline, Cape Cod, and the Islands, where gusts of 30 to 40 mph are possible. Farther inland, northeast wind gusts of 20 to 30 mph are expected, particularly across eastern portions of southern New England. Gusty conditions will persist into tonight and Thursday, with the strongest winds remaining near the immediate coast. While winds gradually diminish across most inland locations, the northeastward movement of the nor'easter may bring another period of stronger winds across the northeastern coastal waters Thursday night into Friday.

The nor'easter is expected to make its closest approach overnight/early Thursday morning, with the greatest precipitation chances remaining across the Cape and Islands. One interesting feature worth watching is a sharp thermal gradient aloft, which could support enhanced frontogenesis and the development of a narrow band of heavier precipitation. There continues to be considerable spread in forecast rainfall amounts, particularly across the outer Cape and Nantucket. Much of this uncertainty appears tied to the exact placement and intensity of the frontogenetic forcing and how far west the associated precipitation band extends. For QPF, utilized a blend of NERFC and WPC guidance, with the highest rainfall amounts expected across Nantucket, where storm totals around 0.50 inches are forecast. Across Cape Cod, rainfall amounts generally range from 0.20 to 0.30 inches. However, ensemble guidance suggests a higher-end scenario of an inch or more across Nantucket, with probabilities of storm-total rainfall exceeding one inch ranging from 30 to 50 percent. While confidence remains lower in precisely where the heaviest precipitation will occur, the greater likelihood is that the enhanced precipitation band remains primarily offshore. As a result, most of southern New England should remain dry, with the greatest potential for measurable rainfall confined to the Cape and Islands.

Nevertheless, while this will not be the quintessential nor'easter for those on land, it certainly will be for the marine community. Large waves and gale-force northeast winds will continue to create hazardous conditions across the coastal waters. While astronomical tides are low, persistent wind and wave action may lead to beach erosion, particularly along east and northeast-facing beaches. Additional details can be found in the marine discussion.

KEY MESSAGE 2...Fairly cool on Friday with a very low chance of an early morning shower over the eastern waters. Otherwise, moderating temperatures and dry conditions are expected for the weekend into early next week.

As the nor'easter gradually pulls away from southern New England, high pressure builds into the region for the upcoming weekend. One feature worth mentioning is a northern-stream shortwave and associated mid-level cold pool passing east of southern New England on Friday. Compared to 24 hours ago, the latest guidance has shifted these features farther east, increasing confidence in dry conditions across the region. An isolated shower cannot be ruled out over the eastern coastal waters, but otherwise dry conditions are expected across southern New England.

Despite the eastward shift in the cold pool, northerly flow aloft will continue to advect colder air into southern New England. Thus, Friday remains the coolest day of the period, with highs mainly in the lower 50s. Depending on how quickly winds decouple Friday night, Saturday morning could feature a frosty start across portions of the interior, with lows in the upper 20s to middle 30s. Otherwise, high pressure promotes subsidence and generally quiet weather through the weekend and into Monday. Temperatures gradually moderate Saturday through Monday, with both daytime highs and overnight lows increasing a few degrees each day as warmer air advects into the region aloft.

Looking ahead to Tuesday, guidance suggests a cold front may approach or move through southern New England sometime during the day. However, uncertainty remains regarding the timing and strength of this frontal passage, and it is still too early to provide much detail on any associated sensible weather impacts.

AVIATION /12Z WEDNESDAY THROUGH SUNDAY/

Forecaster Confidence Levels...

Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent.

12Z TAF Update:

Today and Tonight...Moderate confidence (Ceilings/showers for east terminals)

VFR for west/central southern New England. VFR to MVFR ceilings for BOS/PVD and if VFR SCT lower ceilings are likely to linger around. MVFR likely to develop for the Cape and Islands this morning. Scattered showers in the vicinity of ACK pushing in by early evening. Showers may not reach Cape Cod terminals until after 00Z, but will be in vicinity before that. Showers may be intermittent, with dry periods in between. Potential for low end MVFR and IFR ceilings and visibilities of 3 to 6 SM for Cape/Island terminals overnight.

NE wind gusts of 25 to 35 kt across the Cape and Islands, and 18 to 25 kts farther inland. Gusts gradually diminish this evening across the more inland terminals, while breezy conditions persist closer to the coast.

Thursday...High confidence.

MVFR ceilings across Cape Cod and the Islands improve to VFR between 14Z and 18Z. Winds shift to the north, with gusts gradually diminishing from west to east through the day.

KBOS Terminal...High confidence in TAF.

VFR throughout the TAF period, with increasing cloud cover and ceilings around 5 kft this afternoon into tonight. NE wind gusts of 25 to 30 kt expected through this afternoon, diminishing this evening. Winds gradually turn northerly overnight.

KBDL Terminal...High confidence in TAF.

Outlook /Thursday through Sunday/...

Wednesday Night: Mainly VFR, with local MVFR possible. Windy with gusts up to 35 kt. SHRA.

Thursday: VFR. Windy with gusts up to 35 kt.

Thursday Night: VFR. Windy with gusts up to 35 kt. Patchy frost.

Friday: VFR. Windy with local gusts up to 30 kt.

Friday Night: VFR. Breezy. Patchy frost.

Saturday through Sunday: VFR.

MARINE

Forecaster Confidence Levels...

Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent.

Through Thursday...High confidence.

Dangerous marine conditions will persist through the end of the workweek as a slow-moving nor'easter remains offshore of southern New England. Strong high pressure to the north, combined with the offshore low, will maintain a tight pressure gradient across the coastal waters, resulting in persistent northeast winds and large seas. Gale Warnings have been extended through Thursday evening across the ocean waters, where northeast wind gusts of 30 to 40 knots are expected, with locally stronger gusts possible across the outer waters. Seas will remain rough, potentially approaching 15 feet across portions of the outer waters.

As the nor'easter begins tracking northeast Thursday evening into Friday, the potential for gale-force winds increases across the northeastern coastal waters, including Massachusetts Bay and the waters south of the Merrimack River. As a result, a Gale Watch has been issued for these waters from Thursday evening into early Friday afternoon. While confidence is high in continued hazardous marine conditions, uncertainty remains regarding the magnitude of the strongest wind gusts as the low passes offshore.

Conditions should gradually improve later Friday and into the weekend as the nor'easter pulls farther away from southern New England.

Outlook /Thursday through Sunday/...

Wednesday Night: gale force winds with gusts up to 45 kt. Rough seas up to 14 ft. Rain showers, chance of thunderstorms, patchy fog. Local visibility 1 to 3 nm.

Thursday: Moderate risk for gale force winds with gusts up to 45 kt. Rough seas up to 14 ft. Rain showers.

Thursday Night: Strong winds with gusts up to 40 kt. Rough seas up to 13 ft.

Friday: Strong winds with gusts up to 35 kt. Rough seas up to 13 ft.

Friday Night: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Rough seas up to 11 ft.

Saturday: Winds less than 25 kt. Areas of rough seas.

Saturday Night: Winds less than 25 kt. Local rough seas.

Sunday: Winds less than 25 kt. Areas of seas approaching 5 ft.

BOX WATCHES/WARNINGS/ADVISORIES

CT...None. MA...None. RI...None. MARINE...Small Craft Advisory until 2 AM EDT Thursday for ANZ230-236. Gale Warning until 8 AM EDT Thursday for ANZ231>235-237. Small Craft Advisory until 5 PM EDT Thursday for ANZ250-251. Gale Watch from Thursday afternoon through Friday afternoon for ANZ250-251-280. Gale Warning until 8 PM EDT Thursday for ANZ254>256-281>283.