Cambridge, MA 02141 Weather

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.

Aviation

Forecaster Confidence Levels...

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

06Z TAF Update:

Through 12Z...High confidence.

VFR for most terminals. Ceilings begin lowering to MVFR across Cape Cod and the Islands between 10Z and 14Z. ENE wind gusts of 25 to 35 kt across the Cape and Islands, with localized gusts up to 40 kt possible at ACK. Farther inland, wind gusts of 20 to 25 kt.

Today and Tonight...High confidence overall, though moderate confidence in shower coverage across southeastern New England.