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Hurricane watches up for Maine, New Brunswick, and Nova Scotia as Lee heads north » Yale Climate Connections

After more than eight days as a hurricane, during which time it peaked as a Category 5 storm with 165 mph winds, Hurricane Lee will eventually evolve into a hybrid storm that may be designated post-tropical before it comes ashore near the U.S.-Canada border this weekend. But whatever it’s called, Lee will be a powerful, hazardous storm packing torrential rains, high surf, and tree-felling winds. Tropical storm warnings were in effect late Thursday morning for Bermuda; the southeast Massachusetts coast from Woods Hole to Hull, including the islands of Martha’s Vineyard and Nantucket; and the southwest coast of New Brunswick and much of the Nova Scotia coast. Tropical storm and hurricane watches extended from Rhode Island to Maine.

The forecast for Lee

As of 2 p.m. EDT Thursday, Lee was a Category 1 hurricane with top sustained winds of 85 mph and a central pressure of 957 mb, headed north at 14 mph. Satellite imagery showed that Lee becoming increasingly asymmetric: Most of its thunderstorm activity was on its north side, as dry air wrapped around its south side. This process will continue as wind shear ramps up, though Lee’s large size will help keep the weakening process gradual rather than sudden. The National Hurricane Center predicts that Lee will be at minimal hurricane strength by Saturday morning and will come ashore in northeast Maine or southwest Atlantic Canada as a post-tropical cyclone on Saturday night. By that point, Lee may still be packing top sustained winds of 50 to 70 mph that will affect a broad area.

Heavy rains will be spreading throughout much of eastern New England and Atlantic Canada as Lee approaches. Totals of two to four inches can be expected over far eastern Massachusetts and much of Maine, New Brunswick, and Nova Scotia, with higher totals close to Lee’s eventual landfall location. These rains will fall atop ground that is largely saturated after one of the region’s wettest summers on record, so localized flooding will be a definite risk, even well inland. The sodden ground will make it easier for Lee’s winds to bring down trees and power lines, and residents should be prepared for the possibility of significant power outages. Although some are comparing Lee’s future impact to that of a winter nor’easter, the trees have all their leaves at present and will be more prone to blowing down than in the winter.

Storm surge

Lee’s large size will make it a more formidable storm surge threat than its maximum sustained winds would suggest, particularly since the surge will have very large waves on top of it. Fortunately, the phase of the moon will not be producing unusually high tides this weekend; the highest tides of the month at Cape Cod, Massachusetts, begin occurring on September 26. However, the timing of Lee’s arrival with respect to high tide is crucial, since the range between high tide is very large in this part of the world. Tidal range at Boston is about nine feet; the maximum storm surge flooding there is likely to occur near the high tide cycle around 1 p.m. EDT Saturday. At Eastport, Maine, on the Canadian border, the tidal range is about 18 feet; the maximum storm surge flooding is likely to occur near the high tide cycle at 12:31 p.m. EDT Saturday and potentially during the 12:48 a.m. EDT Sunday high tide as well. The coast of Maine is quite rocky with only a few low-lying areas, so storm surge damage should not be extreme there.

The highest storm surge will occur near and to the right of where the center makes landfall, with western Nova Scotia, New Brunswick, and eastern Maine at highest risk. The counterclockwise circulation of Lee will also pile up a significant storm surge in the Gulf of Maine to the north of Lee, and this surge will get funneled southward past Boston into Cape Cod Bay and into the northern portion of Cape Cod. Since Lee will be weakening as it heads north, the greatest coastal damage from the storm could well be along the north shore of Cape Cod and not to the right of where the center makes landfall.

Lee remains a very large hurricane

Lee is very impressive in size, with hurricane-force winds that extend out up to 90 miles from the center and tropical-storm-force winds that extend out up to 310 miles. As Lee’s hurricane-force winds diminish, its swath of tropical-storm-force winds — strong enough to bring down trees and power lines — may expand even farther. We detailed six reasons for Lee’s large size in our post yesterday, and the Tweet below by Tomer Burg last night shows graphically how much Lee’s winds have expanded over its lifetime using a graphic called a Hövmoller diagram, which tracks time on the y-axis (bottom left to top left) and the diameter of Lee’s flight-level wind speed on the x-axis (bottom left to bottom right).

As of 8 a.m. EDT Thursday, the National Hurricane Center was projecting 30% to 50% probabilities of tropical-storm-force winds (sustained at 39 mph or more, with higher gusts) from the central coast of Maine into New Brunswick and Nova Scotia. The center stressed that the wind speed probabilities beyond 36 hours in its text product and graphics are likely underestimating the risk of those winds occurring. This is because the forecast wind field of Lee is considerably larger than average compared to the wind field used to derive the wind speed probability product.

map shows numerous tracks of historical hurricanes through the Gulf of Maine and across the state
Figure 1. All tropical storms and hurricanes that have moved within 120 miles of Rockland, Maine — an area that includes the entire coast of Maine — in NOAA data extending back to 1851. (Image credit: NOAA Historical Hurricane Tracks)

Tropical cyclone impacts in Maine

On Thursday morning, Maine was under its first Hurricane Watch since one was issued in 2008 for Hurricane Kyle, but the state’s history includes plenty of encounters with tropical and post-tropical cyclones. On August 20, 1991, Tropical Storm Bob made landfall near Bristol with 70-mph sustained winds after having smashed through southeast Massachusetts as a Category 2 hurricane. Although Bob’s damage in Maine was far less than its billion-dollar impact farther south, the storm took three lives in Maine and left $42 million in damage (1991 USD). Wind gusts hit 92 mph in Wiscasset, and 8.24 inches of rain fell at Portland, including 7.93 inches in 24 hours. (See this YouTube clip for a 25-year retrospective on Bob’s impact in Maine.)

A few years before Bob, in 1985, Hurricane Gloria became post-tropical while passing through northwest Maine; strong winds knocked out power to some 250,000 residents for as long as two weeks.

Some of Maine’s most damaging named storms are hurricanes that strike southern New England and then affect Maine after they become post-tropical. Two classic yet contrasting examples from 1954 are Carol and Edna, which rampaged through New England less than two weeks apart.

Carol slammed into eastern Long Island and Connecticut on August 31, 1954, as a Category 3 storm with 115-mph winds, then raced north-northeast along the New Hampshire-Maine border as a post-tropical cyclone with sustained winds of 60 to 80 mph. Maine’s state capital, Augusta, recorded 80-mph winds. Trees were downed across Maine, three people were killed, and there was $10 million in damage (1954 USD), making Carol the state’s costliest disaster on record up to that point. Then, on September 11, Edna passed over Cape Cod as a strong Category 2 hurricane with 110-mph winds. The storm raced over the Gulf of Maine, coming ashore just a few hours later in far eastern Maine near Machias as a powerful post-tropical cyclone. In contrast to Carol, this track put the wetter left-hand side of the storm across Maine, resulting in widespread inland flooding. Eight drownings in Maine were attributed to Edna, and the state’s $25 million in damage smashed the record set by Carol just 11 days earlier.

As evident in Figure 1 above, the steering flow at midlatitudes usually has enough of a westerly component at Maine’s latitude to keep tropical storms and hurricanes angling northeast rather than moving more directly northward into the state. The most recent storm to make landfall as a hurricane on the Maine coast was Gerda, which came ashore near Machias with 80-mph sustained winds on September 9, 1969. Gerda dumped widespread three-to-five-inch rains over southeastern Maine, but damage overall was minimal and there were no fatalities.

photo of waves and spray that appear almost as tall as the homes they're crashing over
Figure 2. A wave crashes over homes on Lighthouse Road in Scituate, Massachusetts on January 4, 2018. The “bomb cyclone” brought the highest water levels on record to Boston. (Image credit: Scott Eisen/Getty Images)

Boston storm surge history

NHC is predicting a storm surge of one to three feet for Boston, but this will likely not rank as one of the top 10 storm surge events for the city. Large storm surges from tropical cyclones are rare in Boston. Of the top-10 highest water levels since records began in 1921, nine have been from nor’easters. Only one has been associated with a tropical system: the Perfect Storm of October 30, 1991, which brought the fourth-highest water level on record to the city. The Perfect Storm was a nor’easter that absorbed Category 2 Hurricane Grace and later evolved into a new unnamed hurricane.

Boston’s highest water level on record is 4.89 feet above mean higher high water, set during the January 4, 2018 nor’easter (dubbed Grayson by The Weather Channel). This storm also holds the all-time high-water record for Bar Harbor, Maine. The storm deepened by an incredible 53 millibars in just 21 hours — one of the fastest intensification rates ever recorded in the Northwest Atlantic. The storm flooded portions of Boston’s financial district, including a subway station.

satellite image of Lee, Margot, and 97L in the Atlantic Ocean
Figure 3. Hurricane Lee (upper left), Hurricane Margot (upper right), and a disturbance named Invest 97L (lower right) as of 1450Z (11:50 a.m. EDT) Thursday, September 14, 2023. (Image credit: RAMMB/CIRA/CSU)

Margot continues to lounge in the remote North Atlantic

Still a hurricane and only gradually spinning down, Margot will be hanging around the central North Atlantic for days more. As of 11 a.m. EDT Thursday, Margot was centered about 710 miles west of the Azores, moving north-northeast at just 6 mph. A broad shield of convection — showers and thunderstorms — continues to surround Margot’s center. Now embedded in the larger Azores-Bermuda high, Margot will slow even further and make a slow cyclonic loop over the next several days. As it spins across the same general area, Margot will churn up cooler waters, and it is predicted to weaken to tropical-storm strength by Friday night. By next week, Margot is projected to accelerate toward Europe as a post-tropical storm.

Invest 97L could be a tropical storm by this weekend

Disturbance 97L, located in the tropical Atlantic midway between the Lesser Antilles and Cabo Verde Islands early Thursday afternoon, had a moderate amount of spin and was generating heavy thunderstorms that were becoming better organized, as seen on satellite images.

As it moves west-northwest to northwest at 10-15 mph over the next several days, 97L will have favorable conditions for development: light to moderate wind shear (5-15 knots), sea surface temperatures of 29-30 degrees Celsius (84-86°F), and a moist atmosphere. In its 2 p.m. EDT Thursday Tropical Weather Outlook, the National Hurricane Center gave 97L two-day and seven-day development odds of 90%. The next name on the Atlantic list is Nigel.

map shows potential tracks for 97L, with most showing it curving away from land
Figure 4. Ensemble tracks for 97L produced on Wednesday night, September 13, extending out eight days. Also shown are the operational (deterministic) model tracks for the GFS (green), and UKMET (blue) models. (Image credit: Tomer Burg)

The top models continue to be in strong agreement that steering currents will take 97L toward the northwest into early next week, angling toward the weakness produced by Margot in the Azores-Bermuda High. If so, the system would most likely avoid the Lesser Antilles and Caribbean. Systems that far north typically recurve before approaching North America, and this is suggested for 97L by most of the current model ensemble members. However, given that any westward bend or ultimate recurve is a week or more away, it is too soon to predict the longer-term fate of 97L with high confidence.

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