Gradually Weakening Storm Now Growing in Size

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NANTUCKET, MA – The 2023 Atlantic Hurricane Season remains a very active one.  There have been 14 named storms, 5 hurricanes, and 3 major hurricanes.  Idalia became the first Atlantic major hurricane to make landfall.  Franklin grew to near Category Five strength while churning out large swells that produced rip currents and dangerous surf along the East Coast.  However, Lee captured a lot of attention by becoming the first Category Five storm, and 7th such one since 2016.  Lee remains a major hurricane despite going through a gradual weakening phase in the Western Atlantic.

Lee was the epitome of rapid intensification.  The storm rapidly deepened from a Category One Hurricane to a Category Five in just 24 hours.  The storm’s sustained wind speed grew by 85 miles per hour over the 24-hour span.  Only two storms have deepened more:  Hurricane Wilma in October 2005 and Hurricane Felix in September 2007.  Minimal central pressure in Lee’s eye dropped to 926 millibars, or 27.35 inches of Hg (Mercury) by the early morning of September 8th.

Shear Halts Lee’s Rapid Deepening

Maximum sustained winds in Lee peaked at 165 miles per hour.  Further strengthening had been forecast, but wind shear began to affect the storm by late Friday morning.  After showing a classic buzzsaw look of a textbook hurricane some 12 to 24 hours before, Lee’s symmetry began to wane as its left flank eroded under the weight of the shear.  The storm underwent further weakening as it went through an eyewall replacement cycle.

The storm began to show signs of re-energizing again as the hostile upper-level conditions eased up some.  After weakening to a Category Two storm with 105 mile per hour winds on Sunday morning (September 10th), Lee ramped up again.  Over 12 hours, the pressure fell from 958 millibars to 954 millibars while the winds increased again to 120 miles per hour.  Despite prognostications that indicated Lee would become a Category Four Hurricane with 140 mph winds, Lee didn’t get stronger.

Lee’s Slowdown Results in Upwelling

Part of the reason was Lee’s reduced forward motion.  As it rapidly strengthened in the Central Atlantic late last week, Lee moved at a pace anywhere between 13 to 15 miles per hour.  By Tuesday afternoon, Lee was meandering in the Western Atlantic at a pace less than half that at 6 to 7 miles per hour.  Slow motion tends to allow the storm to churn up cooler water from deeper levels of the ocean.  When the upwelled water comes to the surface, it depletes the storm’s energy source.

In addition, Lee tracked areas that had been previously traveled through by Franklin and Idalia.  Those storms also produced upwelling, which also cooled the sea surface temperatures in the area of Lee.  Although Lee has been weakening, it has also grown in size.  Its wind field has grown larger.  Tropical storm-force winds in Lee extend some 240 miles from the eye while hurricane-force winds stretch out about 125 miles from the center.  The storm’s width is roughly 500 miles across.

Larger Lee Means More Wave Energy

To give you an idea of what that could mean for coastal residents along the Eastern Seaboard, Hurricane Sandy’s width was 1,150 miles.  Keep in mind though that Sandy did eventually become extratropical and more asymmetrical in shape.  The larger a storm such as Sandy and Lee can be, the more of a water mover it can be.  Over the weekend, Lee generated waves as high as 40 to 50 feet on average.  Hurricane Katrina, another massive storm similarly stirred up the Gulf of Mexico prior to landfall in Buras, Louisiana on August 29, 2005.

The bottom line is that Lee is going to be generating a lot of wave energy as it comes up the East Coast.  The storm will likely pass to the west of Bermuda late Thursday into early Friday morning and then head northward toward New England and the Canadian Maritimes.  Presently, Cape Cod, Martha’s Vineyard, and Nantucket are right in the area of the forecast cone.  Factoring in the size of the storm, it is very likely that tropical storm conditions will be felt in those areas.

Landfall Likely in New England or Canadian Maritimes

Anywhere from coastal Maine to Nova Scotia is a likely landing point for Lee according to the latest forecast.  Nevertheless, it is still too early to tell.  Forecasters are becoming more confident in the track, but still remain cautious.  Lee still has a westward component in its forward motion and continues to move slowly.  For residents along the Jersey Shore, be prepared for another round of dangerous surf and rip currents.

According to Joe Martucci of the Press of Atlantic City, wave heights are forecast to grow to between 4 and 7 feet on Wednesday.  Then, from Thursday to Saturday, the wave heights will rise to between 7 and 13 feet.  Comparing that to Franklin two weeks ago, the waves are forecast to be twice as high. Peak wave heights are likely on Friday, but dangerous surf conditions will linger into Sunday.