Tropical Storm Erin was steadily intensifying in the central tropical Atlantic on Thursday, en route for what may be a textbook route through the northwest Atlantic over the following week. Although there’s a chance Erin will avoid striking any land areas, many coastal areas will be plagued for days by swells, heavy surf, and rip currents, and Erin could pass near enough to Bermuda to merit close attention.
At 11 a.m. EDT Thursday, August 14, Erin was centered about 900 miles east of the northern Leeward Islands, moving west at 17 mph. Erin’s top sustained winds were 60 mph, up from 50 mph earlier Thursday morning and 45 mph on Wednesday evening. The first hurricane-hunter flights into Erin are expected to depart on Thursday night.
Erin was not a large system as of Thursday – its tropical storm force winds extended out only 60 miles – but it’s a safe bet that Erin’s circulation will expand over the coming days as it continues to intensify and especially as it begins to gain latitude, curving poleward by early next week.
Intensity forecast for Erin
A robust core of showers and thunderstorms (convection) was clustered near Erin’s center on Thursday, with extensive convection also popping to the north. Upper-level outflow was gradually becoming well established, another sign of a vigorous tropical cyclone. The National Hurricane Center predicted Erin would become a hurricane on Friday and would continue intensifying through the weekend, as reflected across most model guidance, including the Thursday-morning runs of the high-resolution HWRF, HMON, HAFS-A, and HAFS-B intensity models.
Multiple factors are lining up to keep Erin strengthening. Moderate upper-level wind shear may become strong over the weekend, but it is projected to relax to light-to moderate values of 5-15 mph by early next week. Erin will be in an increasingly moist air mass, with mid-level relative humidities predicted to rise from around 55 percent on Thursday to around 65 percent by Monday. And sea surface temperatures beneath Erin’s path will climb from around 28 degrees Celsius (82 degrees Fahrenheit) on Thursday to 29–30°C (84-86°F) from Sunday onward, which is about 1-2°C (2-4°F) above the average for mid-August. Those surface water temperatures have been made up to 100 times more likely by human-caused climate change, according to the oceanic version of the Climate Shift Index from the nonprofit Climate Central (see Fig. 1).
With all these factors in place, there’s a chance (though not a huge one) that Erin will go through at least one period of rapid intensification, defined as top sustained winds increasing by at least 30 knots (35 mph) in 24 hours. Output on Thursday afternoon from the statistical SHIPS model showed a 27 percent chance Erin would gain 55 knots of strength in the 48 hours ending Sunday afternoon; those odds were 4.7 times higher than the climatological average. In its Thursday morning forecast, the National Hurricane Center brings Erin across the major-hurricane threshold to Category 3 strength (top sustained winds of 115 mph) by Sunday, August 17, with Erin approaching cat 4 strength by Tuesday.
Track forecast for Erin
Erin is currently being steered west by a strong subtropical ridge of high pressure across the subtropical Atlantic. The western end of that ridge is forecast to gradually weaken over the next few days, which should allow Erin to angle increasingly northward with time. The gradual rightward angle is expected to allow Erin to pass just north of the northern Leeward Islands, the Virgin Islands, and Puerto Rico, thus putting those islands on the weaker left-hand side of the storm. This track reduces the odds of highly damaging winds: the Thursday morning forecast included a chance of 20 to 30 percent that sustained winds could bump up to or above gale force (39 mph) over these islands as Erin passes by this weekend.
The National Weather Service in San Juan, Puerto Rico, is flagging a high risk of rip currents along north- and east-facing beaches. Seas are predicted to reach 8-12 feet across exposed Atlantic waters from Saturday night through Monday.
As shown above in Figs. 2 and 3, ensemble models are in near-complete agreement that Erin’s track will thread a needle that could minimize havoc over land areas. Low pressure at upper levels will be dipping into Maritime Canada by early next week, which should further erode the upper-level ridge keeping Erin to the south.
Only a few ensemble members veer Erin far enough west for any possibility of landfall across The Bahamas or on the Southeast U.S. Coast. These straggler tracks are highly unlikely, but they should serve as just enough motivation for keeping tabs on Erin over the next several days. If any such left-outlier track were to become a real possibility, we’d most likely see the bulk of ensemble members shift dramatically westward over the next day or two.
The slam-dunk threat from Erin: Widespread high surf and dangerous rip currents
Regardless of any unwanted surprises from Erin’s track, there’s high confidence in another unwelcome aspect of this storm. Far-flung swells, high surf, coastal erosion, and potentially deadly rip currents will affect the north- and east-facing shores of the Leeward Islands and Greater Antilles this weekend. These will become an increasing hazard in The Bahamas and along the U.S. East Coast early next week, eventually extending into coastal Canada.
A quick-hitting tropical system could briefly affect northeast Mexico and southern Texas
Convection was expanding at midday Thursday in the western Gulf of Mexico and Bay of Campeche associated with a northwestward-moving disturbance designated as Invest 98L. This weak low could organize enough to become a tropical depression (perhaps even a weak tropical storm) before coming ashore in northeast Mexico or far southern Texas by late Friday. Localized rainfall of several inches may occur near the coast. An Air Force reconnaissance mission in progress on Thursday afternoon had found no evidence of any low-level circulation at the time of this writing. In its 2 p.m. Thursday Tropical Weather Outlook, the National Hurricane Center gave this system a 40 percent chance of development before it reaches land. The next name on the Atlantic list is Fernand.
This setup bears some similarity to that of Tropical Storm Barry, which became a tropical depression on Saturday afternoon, June 28, only about 130 miles offshore from Veracruz, Mexico. Barry strengthened into a tropical storm the next morning and made landfall just a few hours later near Tampico, with top sustained winds of 45 mph. Barry’s remnants lingered for days from northeast Mexico into southern Texas, feeding into the catastrophic Hill Country flash floods of July 5. In contrast, the current system is predicted to continue stoutly north after coming onshore; by Sunday or Monday, its remnants may briefly bolster showers and thunderstorms over the Central Plains.
Jeff Masters contributed to this post.
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Great Job Bob Henson & the Team @ Yale Climate Connections Source link for sharing this story.
