Written by Amanda Delaney
Usually May kicks off the start of the New England and Eastern Canadian Maritime cruising season. By then, the gale track shifts to the north and temperatures warm, luring mariners back north from the tropics. Although summer and early autumn are the best times of year to travel in New England and Eastern Canada, there are some weather features that can still change an itinerary or force a vessel to seek shelter. As autumn approaches, not only are there concerns with inclement weather associated with stronger cold fronts but a threat from the tropics can produce a significant risk to these regions. We’ll discuss these threats in detail so you can take the appropriate measures to prepare ahead of time and what type of weather you can typically expect across the region. Let’s explore!
Main Weather Features:
Starting from late May and continuing through August, the main gale track shifts to the north from James Bay eastward through Labrador. Associated cold fronts will extend as far south as 33N-35N and reach the New England Coast and Canadian Maritimes approximately every 3-4 days. These cold fronts generally weaken upon reaching approximately 60W.
By September the main gale track and associated cold fronts shift to the south and, by late month, the gale track runs from Southern Ontario and Quebec eastward through Eastern Newfoundland. Cold fronts become stronger, particularly later in the month, and extend as far south as 32N-33N. These fronts pass through New England and the Canadian Maritimes every 3 days.
Behind these cold fronts, weak highs build to the east across Southeastern Canada, then move southeast over the Northwestern Atlantic Ocean during June through August. During September, these highs are suppressed farther south over the U.S. Mid-Atlantic and Southern New England before moving over the Northwestern Atlantic Ocean. As these highs move over New England and the Canadian Maritimes, patchy to dense fog typically develops during the overnight through morning hours over these regions.
During the late summer and early autumn months, tropical cyclones become active over the Western Atlantic Ocean. Generally tropical cyclones track to the west to west-northwest along the southern periphery of the Bermuda High (a semi-permanent high that remains near Bermuda during much of the summer). If a cold front approaches the U.S. East Coast, the tropical cyclone can turn towards the northwest. If the cold front is slow to move to the east, the tropical cyclone could turn more northward and impact the coasts of New England, or continue to the northeast towards Nova Scotia or Newfoundland. Although these systems can lose their tropical characteristics (becoming extratropical gales or storms) tracking over the colder waters of the Canadian Maritimes, these systems can still produce gale force to, in some cases, hurricane force winds.
However, there will be times that the cold front will move off the U.S. coast quickly forcing the tropical cyclone to turn northeast and remain out to sea. In those cases, stronger winds, large swells and higher than normal tides will impact coastal regions but these areas are spared from a direct strike.
Typical winds and seas:
Ahead of cold fronts, winds will increase from the S-SW Beaufort force 4-5 during June through August, though during mid to late September these winds will increase to force 5-6. Also, severe thunderstorms are possible ahead of stronger cold fronts, which will briefly increase winds and swells. Behind cold fronts, winds will veer and increase to WNW-NNW force 5-6 though become force 6-7 particularly near Newfoundland during mid-late September. Along the New England coast, Nova Scotia, and Newfoundland, swells build S-SW approximately 4-7ft ahead of cold fronts, then become W-NW approximately 5-8ft behind a cold front. These swells will build 1-2ft higher towards later September.
As a ridge of high pressure builds over Southeastern Canada, winds lower and veer from NW-NE-E and become Beaufort force 4 or less. Swells become northeast, east and eventually southeast while lowering to approximately 2-5ft (except in the areas mentioned above regarding limited fetch).
Across the Gulf of St. Lawrence, combined seas during June through September become S-SW-W and build to approximately 3-6ft as cold fronts approach, then become W-NW 4-6ft after cold fronts pass (pre/post frontal passage combined seas tend lowest along coastal areas and higher offshore). Northumberland Strait is prone to large swell differences particularly if the winds flow from the northwest or southeast and this happens to occur during high tide. During the end of September, winds ahead of the strongest cold fronts are generally S-SW force 5-6 and behind cold fronts become W-NW force 6-7. Areas prone to funneling winds such as Cabot Strait, west of Anticosti Island and Northumberland Strait will see winds approximately 1 Beaufort force higher ahead of and behind cold fronts.
As high pressure builds over Southeastern Canada, winds veer N-NE-E and lower to Beaufort force 4 or less and combined seas become NE-E and lower to approximately 3-5ft. For highs that happen to build over the Gulf of St. Lawrence, wind directions will become variable at times and combined seas will be lower to 1-3ft.
Please note that winds/swells will be much higher in/near any tropical cyclones that may move up along or near the coasts of New England and the Canadian Maritimes in late summer through early autumn.
Summer and early autumn are beautiful seasons to visit New England and the Canadian Maritimes. As always, it is best to be prepared for any potential severe weather ahead of cold fronts and for about 12-24 hours of higher winds/swells behind cold fronts. As high pressure builds over the area, patchy to dense fog is possible once the winds lower during the overnight/early morning hours. During this time it is best to wait in port until mid to late morning to allow the fog to dissipate or take the necessary precautions while traveling in low visibility.
Stay informed with reliable weather sources when tropical cyclones become a potential threat to these regions. These systems generally accelerate in the northern latitudes, which will limit the time to prepare or escape to a safe port. With this knowledge and all of these measures taken, a trip to this area of the world is sure to be memorable.
Amanda Delaney is a senior meteorologist employed at Weather Routing Inc. Weather Routing Inc. has been providing routing assistance and forecasts to yachts worldwide for over 50 years.
Contact Weather Routing Inc.
Phone: 1-518-798-1110
E-mail: wri@wriwx.com
Websites: http://www.wriwx.com and http://www.seaweather.net