Hurricane Lee put on an extraordinary feat of rapid intensification in the 24 hours ending at 2 a.m. EDT Friday, increasing its winds by 85 mph as it moved over the record-warm waters northeast of the Leeward Islands. Only two other Atlantic hurricanes in the past 40 years — Felix (2007) and Wilma (2005) — intensified more rapidly. Lee peaked as an extremely dangerous Category 5 hurricane with 165 mph winds early Friday, then weakened slightly to a high-end Category 4 hurricane late Friday morning.
Research by Kieran Bhatia (see below) and others has identified rapid intensification as one of the hurricane phenomena being boosted by oceanic warming from human-induced climate change.
At 11 a.m. EDT Friday, Lee was located about 565 miles east of the northern Leeward Islands, moving west-northwest at 13 mph with top sustained winds of 155 mph and a central pressure of 942 mb. Satellite images early Friday afternoon showed that Lee’s eyewall thunderstorms were not as intense or as symmetric as before, with a region of reduced intensity along its west side. This was being caused by some moderate southwesterly wind shear of 15-20 knots — which was not predicted — that began affecting Lee early Friday morning.
Track forecast for Lee
Lee is expected to move west-northwest at a gradually slowing forward speed through Tuesday, driven by the clockwise circulation around the Azores-Bermuda High to the north. On this track, the system will pass a few hundred miles to the northeast of the northernmost Leeward Islands on Saturday and Sunday, sparing them any major impacts from wind and rain. The National Hurricane Center, or NHC, predicts about a 10-20% chance of tropical storm-force winds in these islands.
On Wednesday, Lee is expected to reach the western edge of the high-pressure ridge steering it and begin to feel the steering influence of a trough of low pressure moving over the U.S. East Coast. This trough is likely to turn Lee sharply to the north, keeping the core of Lee away from the southeastern Bahamas and Turks and Caicos Islands, sparing them from any major impacts from wind and rain. NHC predicts about a 10-20% chance of tropical storm-force winds in these islands.
The exact location and timing of Lee’s sharp northward turn — which is still at the edge of NHC’s five-day forecast window — will strongly determine Lee’s subsequent future. Lee is expected to make its closest approach to Bermuda around Sept. 14-15. However, long-range forecast skill so far in the future is poor, and the threat to Bermuda is unclear. After Lee passes Bermuda, the hurricane poses a landfall threat to the Canadian Maritime Provinces and the Northeast U.S.; the Friday morning runs of the GFS and European models and their ensembles were showing that a landfall as far west as Massachusetts or as far east as Newfoundland were possibilities; a landfall farther to the south along the U.S. East Coast was looking less and less likely. A recurvature out to sea without making landfall is also a good possibility.
The steering of Lee late next week will be determined by the trough of low pressure to the storm’s west, over eastern North America, combined with a ridge of high pressure to Lee’s east, centered along the east coast of Newfoundland. If this ridge is strong enough, it will block Lee’s path to the east, resulting in the hurricane making landfall in the Canadian Maritime Provinces or New England. A weaker ridge would allow Lee to recurve out to sea without making landfall.
The strength of this ridge may depend critically upon how close Tropical Storm Margot gets and how strong it is. If Margot is strong enough and close enough to Lee, Margot will weaken the ridge and engage in a Fujiwhara interaction with Lee — a situation where two cyclones rotate counterclockwise around a common center. This solution was advertised by the 0Z Friday operational run of the European model. A more likely situation is that Margot remains far enough away from Lee that no interaction between the storms occurs, resulting in Lee’s landfall in Canada, as predicted by the Friday morning runs of the GFS model and by most of the ensemble members of both the GFS and European model (Figure 2). In short, this remains a high-uncertainty forecast!
One impact is guaranteed, though: Lee will bring a prolonged period of high surf and dangerous rip currents to the northern shores of the islands of the northeastern Caribbean beginning this weekend and to much of the east coast of North America beginning early next week. High surf will begin to affect the Canadian Maritime Provinces by Wednesday.
Intensity forecast for Lee
The wind shear affecting Lee on Friday is expected to abate by Saturday or Sunday, allowing Lee to take advantage of otherwise favorable conditions for intensification: warm waters of 30 degrees Celsius (86°F) and a reasonably moist atmosphere (a midlevel relative humidity of 55-60%). The total heat content of the ocean waters is expected to peak on Sunday. These conditions should allow Lee to remain at Category 4 or 5 strength through the weekend. The 12Z Friday run of the SHIPS model predicted that over the next four days, Lee’s maximum potential intensity — the strongest it could possibly get under ideal conditions — would be a Category 5 hurricane with 190-195 mph winds. The 11 a.m. EDT Friday NHC intensity forecast called for Lee to maintain Category 4 strength for the next five days and not reach Category 5 strength again, but NHC also acknowledged in its forecast discussion that restrengthening was possible; another period at Category 5 strength can’t yet be ruled out.
Lee may also undergo an eyewall replacement cycle this weekend. This process, common in intense hurricanes, occurs when the eyewall shrinks, grows unstable, and collapses, and a new outer eyewall with a larger diameter replaces it. An eyewall replacement cycle typically weakens the maximum winds of a hurricane by 10-20 mph but spreads out hurricane-force winds over a larger area, increasing the storm surge. The timing of eyewall replacement cycles is difficult to predict.
Most of the intensity models agree that Lee will be a powerful Category 4 or 5 hurricane through Tuesday, then weaken to Category 3 strength by Wednesday because of reduced ocean warmth and an increase in wind shear. Lee’s intensity at the time of any potential landfall in the U.S. or Canada that occurs late next week is impossible to predict so far in advance, but Lee is predicted to expand significantly in size and would be capable of causing significant impacts from its storm surge, winds, and heavy rains, even if it were a tropical storm.
Seven Cat 5s globally in 2023
Lee is Earth’s seventh Cat 5 storm of 2023, using ratings from the Joint Typhoon Warning Center and National Hurricane Center. The 1990-2022 average globally for an entire calendar year is 5.3 Cat 5s, so we are already above average. With the Northern Hemisphere season only about half complete, it is likely there will be more Cat 5s, particularly in the northwest Pacific. The record is 12 Cat 5s in a year, set in 1997. Last year had only three.
This year is now the first time on record that there has been at least one Cat 5 observed in every major ocean basin prone to tropical cyclones. In addition to Lee in the Atlantic, we had Cat 5s in the northeast Pacific (Jova), northwest Pacific (Super Typhoon Mawar), North Indian (Cyclone Mocha), the South Indian (Cyclone Freddy and Cyclone Ilsa), and Southwest Pacific (Cyclone Kevin). Thanks go to Jasper Deng for this stat.
Tropical Storm Margot on track to intensify this weekend
Though still a minimal tropical storm on Friday, Margot may be prowling the Atlantic for a long while — perhaps even longer than Lee. At 11 a.m. EDT Friday, Margot was centered in the eastern tropical Atlantic about 600 miles west-northwest of Cabo Verde, with top sustained winds of 40 mph and a central pressure of 1005 mb, headed west-northwest at 17 mph.
The expansive field of showers and thunderstorms, or convection, around Margot was not especially well organized at midday Friday. Margot will be moving west-northwest this weekend over warm waters (around 28 degrees Celsius, or 82 degrees Fahrenheit), within a modestly moist atmosphere (midlevel relative humidity around 55-60%). Margot’s main nemesis will be persistent westerly wind shear of 15-25 knots, which was pushing most of Margot’s convection away from its low-level center on Friday — never a good sign for the health of a tropical cyclone. Despite the strong shear, forecast models are in strong agreement that Margot will gradually intensify over the next several days. The National Hurricane Center predicted on Friday that Margot will reach hurricane strength by Sunday and remain a Category 1 storm through at least Wednesday.
Margot itself will not threaten any land areas for the next few days, if ever, and it will most likely remain far enough east of Lee (at least 1,000 miles or 1,600 kilometers) to minimize any influence on their mutual motion that would arise from the Fujiwhara effect, as discussed above. Even so, Margot could still influence the fate of Lee. As Margot angles toward the north early next week, it will help break down the sprawling Bermuda High now steering Lee toward the west-northwest. The evolution of that high will play a crucial role in Lee’s future, as noted above.
Next tropical wave
A number of members of the GFS and European model ensembles are showing development could occur by the middle of next week in the central tropical Atlantic of a tropical wave predicted to move off the coast of Africa early next week. This wave is not yet being highlighted by NHC in its Tropical Weather Outlook.
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