Now the system is set to pass close to Bermuda as a high-end storm before charging at the Canadian Maritimes, lashing Nova Scotia with winds potentially gusting upward of 100 mph. By then it may no longer be tropical, but it could be just as strong as a high-end Category 1 or low-end Category 2 hurricane.
It comes amid a sudden awakening of tropical storm activity in the Atlantic. Tropical Storm Gaston developed west of the Azores on Tuesday, and two other tropical waves in the eastern Atlantic are of interest.
The most concerning disturbance, however, is just east of the Windward Islands. That one is set to cross the Lesser Antilles, reaching the Caribbean later this week and entering an extremely favorable environment for intensification. The odds of a hurricane entering the Gulf of Mexico are increasing, and people along the Gulf Coast, including in the United States, should pay close attention.
At least four killed in Puerto Rico during Hurricane Fiona, FEMA says
The sudden uptick in Atlantic tropical activity comes just a week after the climatological peak of hurricane season, meaning it’s right on schedule. August was the first since 1997 not to feature a single named storm developing anywhere across the basin, but next week may reinforce the adage that it only takes one storm for a quiet season to turn catastrophic.
As of midmorning Wednesday, Fiona was a Category 4 hurricane with winds in the eyewall sustained at up to 130 mph. It was moving due north at 8 mph about 700 miles southwest of Bermuda. The British overseas territory has been placed under a tropical storm warning and a hurricane watch, the latter in case the projected track of Fiona swings closer to the island.
On a recent reconnaissance flight, a Hurricane Hunter aircraft encountered winds of 144 mph at 8,530 feet altitude in the eyewall. That’s supportive of surface winds around 130 mph.
Infrared satellite revealed a mature eye and cloud-top temperatures of minus-112 degrees Fahrenheit, which indicates clouds towering about 50,000 feet tall. It appeared Fiona may be fending off a bit of dry air from the north and west.
The Hurricane Hunters also found a roughly 14- or 15-degree spike in air temperature within the eye. That’s a sign of intensity. Air rises in the eyewall and subsides in the eye, sinking, warming, drying up and hollowing out a void of cloud cover. That’s why the strongest hurricanes’ eyes are often the hottest and sometimes feature sunshine.
Transition into Canadian superstorm
Fiona is set to pass west of Bermuda on Thursday night or Friday morning. The island will probably see tropical storm conditions, or winds of 39 mph or greater, along with heavy downpours in the outer rain bands. Afterwards, it will continue north while being tugged back to the west by an approaching mid-latitude low-pressure system.
As Fiona approaches the Canadian Maritimes, it will begin to tap into jet stream energy, converting into an “extratropical,” or nontropical, low. It’s unclear whether Fiona will still retain tropical characteristics as it barrels into Canada early Saturday. Regardless, wind gusts of 100 mph or more are likely.
Exacerbating the winds will be a “pressure dipole,” or the juxtaposition of an intense high-pressure system south of Greenland. The proximity of two extreme systems — one a storm with low pressure and the other a dome of warm, high pressure — will amplify the winds because of the extreme pressure gradient, or change in air pressure with distance.
Euro Model is in with a record-breaking (if it happens) 935mb Fiona superstorm into eastern Nova Scotia – Western Newfoundland Sat morning. With this intensity and the strong high to its NE, the waves in the North Atlantic will be mountains! pic.twitter.com/F1sYbWQfhp
— Bill Karins (@BillKarins) September 20, 2022
There are signs that Fiona could obliterate minimum air pressure records for September and potentially for all months on record in Nova Scotia. The lowest air pressure recorded there was 950.5 millibars. (Typical sea level air pressure is around 1,015 millibars; any deficit represents “missing” air that has a vacuum-like effect, which results in strong winds.) Models are suggesting Fiona might have an air pressure around 930 millibars. Superstorm Sandy in 2012 was around 940 millibars when it crashed into New Jersey.
In addition to extreme winds, a storm surge of 5 to 8 feet would be possible, along with offshore waves 80 feet high. Extremely dangerous conditions will result for mariners.
Also in the Atlantic is the newly minted Tropical Storm Gaston. It’s 775 miles west of the Azores and has winds of 65 mph.
On satellite imagery, Gaston’s convection, or thunderstorm and downpour activity, was not as robust as it was 24 hours ago. It also may be beginning to acquire nontropical characteristics; the arcing band of thunderstorms east of the center is suggestive of a cold front taking shape. Truly tropical systems do not have fronts.
The storm will slowly meander northeast over the coming days, potentially bringing gale-force winds to the Azores this weekend before weakening and drifting westward.
A developing gulf, Caribbean threat
There are three other areas to watch in the Atlantic. One is over the east central Atlantic and has a low-to-medium chance of development in the long range, but near-term strengthening is unlikely at present. There’s another tropical wave over Senegal that could begin to develop as soon as it moves offshore of the African coastline in the coming days.
Then there’s a third system near the Windward Islands. That’s the one that could be a big problem.
In the coming days, it will slip through the Lesser Antilles with some wind and rain, but shear — or a disruptive change of wind speed and/or direction with height — will preclude its further development through the end of this week. That shear stems from outflow, or high-altitude exhaust, exiting Fiona well to the north.
But by Sunday or Monday, the shear will relax. The system, dubbed 98L, will find itself in an extremely favorable environment characterized by bathlike seawater nearing 90 degrees. That means the Caribbean is replete with untapped “oceanic heat content,” or fuel to support an intense cyclone. Shear will be weak, and high pressure aloft will help fan exhaust air away from 98L. That evacuation of “spent” air will make it easier for the fledgling storm to inhale warm, humid air in contact with the ocean from below. That will foster intensification.
From there, it’s impossible to know exactly when the storm will begin to curve north. Cuba or the Yucatán Peninsula could be in play, or the storm could whirl directly into the Gulf of Mexico.
One thing’s for certain: Putting a developing storm in the Caribbean with low shear and toasty water temperatures in September is like lighting fireworks inside a tent. You don’t know exactly which way the firework will go, but once the fuse is lit, something’s going to get hit.