Hurricane Erin embarks on a ferocious week of churning the Atlantic » Yale Climate Connections

Newly designated Hurricane Erin is predicted to roil the waters of the Atlantic for a week or more as it arcs westward and northward. Erin is predicted to be a major hurricane (Category 3 or stronger) for at least three days, likely peaking as a Cat 4 as it traverses unusually warm waters between The Bahamas and Bermuda. Erin’s powerful, expanding circulation will lead to days of high surf, beach erosion, and deadly rip currents from the Greater Antilles to The Bahamas, Bermuda, and the Southeast U.S. coast, eventually spreading northward to Atlantic Canada.

As of 11 a.m. EDT Friday, August 15, Erin had reached minimum hurricane strength, with sustained winds of 75 mph and a central pressure of 996 millibars. The Cat 1 storm was centered about 460 miles east of the northern Leeward Islands. Moving west-northwest at 18 mph, Erin had begun a long-awaited rightward bend that should take it just north of the Leewards and Puerto Rico. Tropical storm watches were out across most of the northern Leewards: even though landfall is not expected there, the weaker left-hand side of Erin could still bring winds near tropical-storm strength as it passes just north of these islands, along with locally heavy rains that could lead to flash flooding.

Erin is the Atlantic’s first hurricane of the year, arriving on the heels of four relatively weak tropical storms. On average (1991-2020), the year’s first Atlantic hurricane develops on August 11, so Erin is just four days “late”. Hurricanes have been arriving “early” for more than a decade now: the last time the Atlantic saw its first hurricane of the year develop after the climatological average date was in 2013, when Humberto reached hurricane strength on September 11. (We can expect to see another Humberto sooner rather than later, as the six-year rotation of Atlantic hurricane names means that this year’s list is the same as 2013’s.)

Intensity forecast for Erin

Erin was already an impressive hurricane at midday Friday. It might have developed even more quickly had Saharan dust and dry air not infiltrated its well-defined circulation at the outset. Showers and thunderstorms (convection) were gradually consolidating around Erin’s core on Friday, with squalls extending well to the west and north.

Conditions are ripe for Erin to become a formidable hurricane. The mid-level atmosphere surrounding Erin will moisten with time, as relative humidity will increase from around 55 percent on Friday to around 65 percent early next week. Erin’s robust circulation is expected to help the hurricane fend off potential negative effects from the strong wind shear (10-20 knots) expected to prevail from late weekend into early next week. And Erin will be traveling over exceptionally warm water in the area east and north of The Bahamas. Sea surface temperatures beneath Erin’s path will rise from around 28-29 degrees Celsius (82-84 degrees Fahrenheit) on Friday to 30°C (86°F) by early next week. These values, which are up to 1-2°C (2-4°F) warmer than average for mid-August, 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).

The Friday morning forecast from the National Hurricane Center predicts a period of rapid intensification from Friday evening to Saturday evening, by which point Erin is forecast to be a Category 3 major hurricane with top sustained winds of 120 mph. (Rapid intensification is defined as top sustained winds increasing by at least 30 knots or 35 mph in 24 hours.) Even with wind shear increasing by late in the weekend, the center still predicted Erin to reach Category 4 strength by late Sunday, perhaps continuing as a major hurricane through midweek with minor fluctuations in strength.

The 12Z Friday run of the SHIPS statistical model gave Erin a 23% chance of gaining 30 knots of strength in 24 hours. Those odds are 3.3 times higher than the climatological norm. The newer DTOPS model within SHIPS had substantially higher odds, at 48%.

Track forecast for Erin

The wealth of model ensemble forecasts now available to forecasters has been proving its value with Erin. While individual model runs shifted west or east at times, especially earlier in the week, the ensembles have mostly stayed the course. The model consensus makes it clear that Erin will almost certainly take a best-case track between The Bahamas and Bermuda, most likely avoiding any landfall and staying well east of the U.S. East Coast. The main exception is Bermuda, where a few ensemble members project a direct hit or a near-miss. Even if it avoids a direct landfall, Bermuda is likely to end up on the more intense right-hand side of Erin, with potentially significant impacts.

Down the line, Erin may end up tracking over or near Newfoundland and Labrador late next week, most likely as a powerful post-tropical storm.

Elsewhere in the Atlantic

We’re heading toward the peak of Cabo Verde season, when easterly waves streaming off the coast of Africa often serve as the seeds of tropical cyclones in the Atlantic. Several such disturbances are already lined up, and at least one of these may develop next week as it crosses the Main Development Region of the tropical Atlantic. Long-range ensemble models, particularly the GFS, suggest this system – assuming it develops – would traverse the tropics at a lower latitude than Erin. Residents from the Leeward Islands toward the Greater Antilles will want to keep an eye out, as any such development could begin to affect these islands as soon as next weekend (August 23-24) if it were to materialize. Steering currents will depend in part on how Erin evolves, so it’s much too soon for any firm long-range prognosis.

A disturbance over the western Gulf dubbed Invest 98L continued to produce showers and thunderstorms as it rolled onto the coast of southern Texas at midday Friday. Hurricane hunters detected no low-level circulation in this system, and in its 2 p.m. EDT Friday Tropical Weather Outlook, the National Hurricane Center gave this system a near-zero chance of development.

Jeff Masters contributed to this post.