Jeff Masters Hurricane Blog

Hurricane Lee slows and reorganizes » Yale Climate Connections

Hurricane Lee continued to churn in the western North Atlantic on Monday, slowing down as it prepares to make a long-anticipated turn likely to bring it near Atlantic Canada or New England by this weekend. Regardless of any potential landfall, Lee will push immense amounts of water toward the U.S. East Coast later this week, causing widespread swells, rough surf, rip currents, and beach erosion.

As of 11 a.m. EDT Monday, Lee was a Category 3 hurricane with top sustained winds of 120 mph, centered about 400 miles north-northeast of Puerto Rico. Lee’s structure had improved since Tuesday, but the hurricane was still plagued with moderate wind shear and intrusions of dry air that have limited its reorganization. Moreover, reconnaissance flights on Monday morning found that Lee had concentric eyewalls, which will likely lead to another eyewall replacement cycle (EWRC) and make it more difficult for the hurricane’s inner core to strengthen dramatically.

Some gradual intensification is possible as wind shear relaxes somewhat and Lee continues to pass over very warm waters (30 degrees Celsius or 86 degrees Fahrenheit) with ample deep-ocean heat content. The National Hurricane Center predicted that Lee would briefly hit minimal Category 4 strength on Tuesday.

As Lee moves slowly northwest, swells and rough surf can be expected today and Tuesday on north-facing shores of the Greater Antilles, gradually working their way into the Bahamas and Bermuda. Lee will stay far enough north that there is a less than 5 percent chance of tropical-storm-force winds reaching Puerto Rico, Hispaniola, and the U.S. Virgin Islands.

Track forecast for Lee

The large-scale outlook for Lee’s movement has changed very little over the past several days. By midweek, Lee will be rounding the southwest side of a large ridge of high pressure in the North Atlantic and will begin to feel the influence of an upper trough over eastern North America. Forecast models are in firm agreement that these factors will induce a fairly sharp northward turn around Wednesday, and a gradual northward acceleration through the rest of the week.

Figure 1. Tracks of the operational European, GFS, and UK Met Office model runs (dark red, green, and blue) starting at 0Z Monday (8 p.m. EDT Sunday, September 10, 2023), and members of the ensembles for these three models (dark lines). The dots indicate the forecast positions for each model run as of 2 a.m. Sunday, September 17. (Image credit: Tomer Burg)

The exact location and timing of Lee’s midweek turn are still difficult to predict, and these will influence how far west or east Lee is positioned as it accelerates northward. The precise interaction of the ridge and trough at higher latitudes will also shape Lee’s trajectory. There is sustained and increasing agreement among models that Lee will pass to the west of Bermuda (which NHC gave a 43% chance of experiencing tropical storm-force winds) and head toward Atlantic Canada – most likely Nova Scotia and New Brunswick – but the track could still veer far enough west to reach New England, or far enough east to make an initial landfall in Newfoundland. The 11 a.m. Monday five-day forecast cone extended to Nantucket Island in far southeast Massachusetts, and we can expect other parts of New England and Atlantic Canada to enter the cone over the next couple of days. NHC gave Nantucket a 19% chance of experiencing tropical storm-force winds by 8 a.m. EDT Saturday.

Intensity forecast for Lee

Monday and Tuesday will likely mark Lee’s second and final peak of intensity after the hurricane briefly hit Category 5 strength on Friday. As it heads northwest, Lee will be moving over cooler waters churned up by the recent passage of Hurricanes Franklin and Idalia. Wind shear will increase by late week as well, and by Friday Lee will be crossing the Gulf Stream and approaching much cooler waters to its north. Lee is predicted by NHC to weaken to Category 1 strength by Friday.

As it moves north, Lee will also enlarge, its winds weakening but spreading over a much larger area. The expanded wind field will help drive the widespread effects of high surf throughout the U.S. East Coast and into Atlantic Canada.

Margot near hurricane strength, but no threat to land

As of 11 a.m. Monday, Tropical Storm Margot was located in the remote central Atlantic, about 1,245 miles northwest of the Cabo Verde Islands, headed north at 10 mph. Margot’s top sustained winds were 70 mph, and satellite images showed that the storm was near hurricane strength, with a prominent eye.

Margot is predicted to peak as a Category 1 hurricane with 90 mph winds on Wednesday, then slowly weaken. Margot is not a threat to any land areas this week, but the Azores Islands may need to be concerned about the storm next week.

A new African wave has the potential to develop

A tropical wave newly-emerged from the coast of Africa (Invest 98L) is generating disorganized heavy thunderstorms along the coast of Africa. The wave is expected to move west to west-northwest at 15-20 mph, and merge later this week with another tropical disturbance (Invest 97L) located just west of the Cabo Verde Islands. This combined system may develop over the central tropical Atlantic late this week, according to the GFS and European models and many of their ensemble members.

In their 2 p.m. EDT Monday Tropical Weather Outlook, NHC gave this system 2-day and 7-day odds of development of 0% and 60%, respectively. Long-range forecasts currently show that this wave is likely to take a more northwesterly track later in the week, making it unlikely to pass through the Lesser Antilles Islands (see Tweet above), though a subsequent westward turn cannot be ruled out. The next name on the Atlantic list of storms is Nigel.

Figure 2. The circulation of former Medicane Daniel spinning over eastern Libya and western Egypt on September 11, 2023. (Image credit: Copernicus/Sentinel, via @kosmi)

Catastrophic flooding in Libya from Medicane Daniel; thousands of deaths feared

As this post was finalized, reports were accumulating of what may be one of the worst weather disasters in modern African history. Torrential rains and catastrophic floods have affected multiple locations in Libya. The worst-hit location appears to be the port city of Derna on the Mediterannean coast (population around 90,000), where at least two confirmed dam failures led to severe flooding. The prime minister of eastern Libya said in an interview that at least 2,000 people are feared dead in the Derna area, according to the Egyptian news site Ahram and the Associated Press. At least 37 flood-related deaths have been confirmed elsewhere in Libya.

The rains were produced by a storm that began as an upper-level low in southeast Europe, causing extreme rains and flooding in Greece and Turkey. As the low, named Daniel, moved southward over the warm waters of the Mediterranean, it evolved into a medicane (Mediterranean tropical-like cyclone) and continued into Libya on Saturday.

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