After five full days as Invest 91L and nearly nine days after rolling off the coast of Africa, the disturbance we’ve been tracking through the tropical Atlantic all week finally gathered enough organization to become Tropical Storm Earl late Friday night, the fifth named storm of the Atlantic hurricane season and second named storm to form in just over 24 hours.
Granted, Earl isn’t about to win any beauty contests – resembling a Saturday morning side of scrambled eggs on satellite – but Air Force Hurricane Hunters investigating the system until sundown Friday found a well-defined circulation and winds at flight level (around 2,500 feet above the ocean) as high as 53 mph some 60 miles north of the center, suggesting maximum sustained surface winds near 40 mph – the threshold for tropical storm intensity – after a standard 75 percent adjustment factor is applied.
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The only missing piece to NHC’s upgrade of 91L to Tropical Storm Earl was persistent thunderstorms over the occasionally exposed center. Thunderstorm activity continued to bubble into the late evening hours, prompting the upgrade to Earl.
The disturbance that became Earl had been inching along through the Atlantic this week at speeds as slow as 5 mph due to weak subtropical high-pressure steering.
If you’re a regular reader of the daily newsletter, you’ve read ad nauseum about the slow movement and higher-than-average forecast uncertainty with this one since last weekend.
A comparison of the five-day forecast from the European model from Monday morning to the location of Earl Saturday shows a nearly 350-mile difference – almost three times the typical five-day forecast error – despite a reasonable representation of the system’s strength. Weak steering and nascent circulations can together throw forecasts out of kilter.
Thankfully, despite a track a little south than initially forecast by the models, Earl remains lopsided, with most of its weather – both heavy rain and squally winds – north and east of its still-at-times exposed center.
This means the worst of the storm should stay north of the Greater Antilles, including Puerto Rico and the U.S. Virgin Islands, Saturday and Sunday. Though none of the islands are under a tropical storm advisory, periods of heavy rain and tropical squalls are still possible on the tail of Earl into early next week.
For us in South Florida, Earl isn’t a concern, as a dip in the jet stream will carve an escape route for the storm to turn northward next week and begin moving northeastward and away from the southeast U.S. and Bahamas.
Although conditions aren’t expected to permit much strengthening in the near term, by mid-to-late next week – after it begins to pull northward – Earl may have an opportunity to grow much stronger.
Though still a long ways out, interests in Bermuda will want to continue to follow the progress of Earl during the upcoming week.
Aside from Earl, the only other system we’re following in the Atlantic is Danielle, which formed quickly on Thursday over the abnormally warm waters of the open north Atlantic.
Despite an impressive presentation and initial forecasts calling for a Category 2 hurricane by Sunday, Danielle surprised forecasters by weakening back to a tropical storm Saturday morning. Even though it’s forecast to regain hurricane strength, Danielle will remain over the open waters of the far north Atlantic.
The rest of the tropical Atlantic looks quiet into the holiday week ahead.