Fears that a quiet Atlantic would leap into a more hectic back-loaded season are coming to pass this week. Fiona became the year’s first major hurricane early on Tuesday, September 20. A new tropical depression further north may become Tropical Storm Gaston by midweek. And a disturbance dubbed Invest 98L in the central tropical Atlantic has the potential to become a serious threat by early next week as it moves toward the western Caribbean and perhaps onward to the Gulf of Mexico.
Fiona’s ascent to major hurricane status brings the 2022 Atlantic tally to six named storms, three hurricanes, and one major hurricane. The 1991-2020 climatological averages for this point in the season are 9.7 named storms, 4.5 hurricanes, and 2.0 major hurricanes. The first major hurricane of the season typically appears by September 1. This year’s accumulated cyclone energy (ACE) index is currently running 50% of average for the date, but it will be closer to average by the end of the week, as Fiona churns the Atlantic at major hurricane strength.
On Tuesday, the five-year anniversary of catastrophic Hurricane Maria in Puerto Rico, the island was just beginning to catch its breath after a soggy, windy assault from Fiona on Sunday and Monday. The rains on the island were dwindling, but Fiona had dumped catastrophic amounts of rain: more than 12″ over large parts of Puerto Rico, triggering widespread flash flooding that likely cost billions, the Governor of Puerto Rico said. A number of stations recorded more than 25 inches of rain, and the state 24-hour precipitation record may have been broken: A rain gauge near Caguas reported an astonishing 27.14 inches of rain in the 24 hours ending at 10:15 a.m. EDT Monday, which if confirmed would set a new 24-hour rainfall record for Puerto Rico. The old record is 23.75 inches (this is a 24-hour precipitation record, not merely a calendar-day record, an official at NOAA confirmed in an email).
Virtually the entire island lost power at the storm’s peak, and restoration efforts are still in early stages. The website poweroutage.us estimated at midday Tuesday that power had been restored to about 20% of the 1,468,223 electricity customers it tracks in Puerto Rico. Approximately 25% of the island lost cell phone service and/or water on Monday. One indirect death in Puerto Rico was blamed on Fiona.
Fiona brought more than eight inches (203.2 mm) to much of the eastern tip of the Dominican Republic. The maximum 5-day rainfall ending at 8 a.m. EDT Tuesday at a major airport was 13.95 inches (354.4 mm) at La Romana; Punta Cana received 11.35 inches (288.3 mm). Two deaths in the Dominican Republic were blamed on Fiona.
Turks and Caicos Islands
Fiona moved through eastern parts of the Turks and Caicos Islands early Tuesday. Western parts of Fiona’s inner core appear to have affected Grand Turk Island, and the storm moved almost directly over the Caicos Islands, though the strongest winds were on Fiona’s eastern side, away from the Turks and Caicos. On Tuesday morning, an unofficial weather station on South Caicos reported sustained winds of 77 mph, gusting to 98 mph.
Forecast for Fiona
As of 11 a.m. EDT Tuesday, Fiona was centered about 40 miles north-northwest of Grand Turk Island, moving north-northwest at 9 mph. Fiona was a low-end category 3 storm with top sustained winds holding at 115 mph. The hurricane appeared to be undergoing an eyewall replacement cycle, a process common in intense hurricanes where the inner eyewall collapses and is replaced by an outer eyewall with a larger diameter. This process will often weaken a hurricane’s top winds by 10-20 mph, but spread hurricane-force winds over a wider area.
Conditions are favorable for Fiona to remain a major hurricane for the next several days. Though wind shear of 15-20 knots could be a limiting factor, Fiona will be drawing on very warm sea surface temperatures of 29-30 degrees Celsius (84-86°F), with ample deep oceanic heat content through Wednesday. With one or more periods of strengthening possible between now and Thursday, Fiona could reach category 4 strength, as predicted by the National Hurricane Center. It’s also possible that one or more eyewall replacement cycles will keep Fiona just shy of cat 4 strength. In either case, Fiona will remain a formidable storm through midweek, and its wind field will gradually expand. Waves near the center of the hurricane are predicted to reach 40-55 feet, which will generate large swells and rip currents along parts of the U.S. East Coast over the next several days, and Maritime Canada late in the week.
Ensemble model runs increasingly agree that Fiona will track far enough west of Bermuda to spare the island a direct hit. Nevertheless, Fiona’s gale-force winds will extend almost 200 miles east of the center on the storm’s stronger right-hand side on Thursday night, when Fiona is expected to be passing 50 to 150 miles west of Bermuda. Thus, tropical storm conditions are quite likely in Bermuda, and hurricane-force winds cannot yet be ruled out. The 11 a.m. EDT Tuesday Wind Probability Forecast gave Bermuda an 81% chance of receiving tropical storm-force winds, and a 21% chance for hurricane-force winds.
Fiona a significant threat to Canada
Fiona is predicted to maintain major hurricane strength unusually far to the north, thanks to sea surface temperatures between Bermuda and Canada that are up to 2 degrees Celsius (3.6°F) above average. The 11 a.m. EDT Tuesday NHC forecast put Fiona near the eastern tip of Nova Scotia on Saturday morning as a category 2 hurricane with 100 mph winds; the Wind Probability Forecast gave several locations in Newfoundland and Nova Scotia 10-23% odds of experiencing hurricane-force winds this weekend. These odds will likely rise as Fiona approaches Canada and the track and intensity of the hurricane become clearer.
As Fiona approaches Canada, the hurricane will merge with a trough of low pressure, transition to a hurricane-strength extratropical storm, and slow down, subjecting Canada to an unusually long and severe battering by what may be one of the strongest storms ever to affect the region. The NOAA/NWS Weather Prediction Center is explicitly forecasting a central pressure below 960 mb just south of Atlantic Canada on Saturday. Such a value would threaten the lowest pressures on record in that region for September. (An all-time record is less likely, since winter storms can be fierce in this area).
The Tuesday morning runs of the GFS and European models are even more eye-opening, predicting that Fiona would reach Nova Scotia and Newfoundland on Saturday morning with a central pressure below 940 mb. According to NOAA, the all-time lowest pressure ever recorded in this region was 940.2 mb on January 21, 1977 (see Tweet below by David Roth). Wind, storm surge, and flooding from heavy rains will all be significant hazards from Fiona in Canada; with the trees still in full leaf, major tree and power line destruction will likely occur.
Tropical Depression 8 forms in central Atlantic, poses no threat to land
Tropical Depression Eight (TD 8) formed at 11 a.m. EDT Tuesday in the central North Atlantic, about 1110 miles west-southwest of the Azores, but poses no threat to land. Satellite imagery on Tuesday afternoon showed a well-developed surface circulation and a modest area of heavy thunderstorms. Conditions favor slow strengthening, and TD 8 is likely to become Tropical Storm Gaston by Wednesday. Steering currents favor a slow northeasterly track, and by Saturday, TD 8 may get caught in Hurricane Fiona’s circulation and get swung more to the north, putting the system in a region with higher wind shear and colder waters and thus ending its life as a tropical cyclone.
Disturbance 98L a potential significant threat for the Caribbean
A more serious concern is a tropical wave about 500 miles east of the Windward Islands on Tuesday afternoon, which was headed west at 15-20 mph. This disturbance, which NHC on Tuesday morning designated Invest 98L, has the potential to be trouble for the Western Caribbean toward the end of this week. Satellite imagery on Tuesday afternoon showed that the thunderstorm actively had grown more concentrated in 98L since Monday, and a satellite wind instrument (ASCAT) revealed on Tuesday morning that a broad surface circulation might be starting to form. 98L had conditions ripe for slow development, with moderately high wind shear of 15-20 knots, warm sea surface temperatures of 29.5 degrees Celsius (85°F), and a reasonably moist atmosphere (mid-level relative humidity of 65%).
The wave is predicted to bring heavy rain showers and gusty winds to the Windward islands on Wednesday and enter the southeastern Caribbean on Thursday. Close proximity to the coast of South America may impede development on Wednesday and Thursday, and so too will wind shear, predicted to rise to the high range, 20-25 knots.
Odds for development will rise on Friday, when 98L will have gained some latitude and entered the central Caribbean. With warm water, moderate wind shear, and a moist atmosphere expected in the central and western Caribbean Friday through early next week, conditions will be ripe for development. All three of the top models for tropical cyclone genesis – the GFS, European, and UKMET – showed 98L developing into a tropical depression, as did a number of the GFS and European model ensemble forecasts. Many of these model runs went on to produce a robust hurricane in the western Caribbean and into the Gulf of Mexico next week. Such an outcome is certainly plausible, but given the extended time range, it is too soon right now to place high confidence on any particular scenario, despite the general model consensus.
In its 2 p.m. EDT Tuesday Tropical Weather Outlook, NHC dramatically boosted the 2-day and 5-days development odds of 98L to 60% and 80%, respectively. The same outlook also flagged the far eastern tropical Atlantic with 5-day development odds of 20% for a new tropical wave coming off Africa later this week. The next two names on the Atlantic list of storms after Gaston are Hermine and Ian.
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