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HomeCats NewsCat 4 Fiona steams toward Canada; Caribbean disturbance 98L a major concern...

Cat 4 Fiona steams toward Canada; Caribbean disturbance 98L a major concern » Yale Climate Connections

Hurricane Fiona was accelerating poleward at midday Thursday on a collision course with Atlantic Canada, where it may rank among the strongest storms in that country’s history. A rare hurricane watch was issued Thursday by the Canadian Hurricane Center for portions of Nova Scotia, Newfoundland, and Prince Edward Island. Fiona may become a post-tropical cyclone just hours before reaching the coast, but hurricane-scale impacts are likely whether or not it does.

Fiona’s top sustained winds at 2 p.m. Thursday were 130 mph, at the low end of the category 4 range; the central pressure was holding steady at a very low 936 mb. Fiona was located about 345 miles west-southwest of Bermuda, and on its steady north-northeast track, Fiona is expected to pass roughly 100-150 miles northwest of the island on Thursday night. A direct hit is not expected, but given the size and strength of Fiona’s expanding circulation – including hurricane-force winds that extend up to 70 miles from its center – Bermuda was under a hurricane warning on Thursday.

Fiona’s passage will be close enough to give Bermuda more than a 90% chance of tropical storm conditions, including the risk of sustained winds 40-70 mph or stronger and intense squalls dropping 2 to 4 inches of rain. Large swells causing rip currents and dangerous surf will be a hazard not only in Bermuda, but also along much of the U.S. East Coast and Maritime Canada during the next few days.

As Fiona accelerates north-northeast on Friday, a strong midlatitude storm system will be approaching from the northwest, making for an exceptionally powerful double whammy. The National Hurricane Center predicts that Fiona will still be a major hurricane with sustained winds of 120 mph at 8 p.m. EDT Friday. On Friday night, the approach of the midlatitude upper-level trough will lead to an unusually quick conversion to an intense post-tropical cyclone – briefly enveloping a warm hurricane core at lower levels within a fast-evolving, higher-latitude-type storm. This phenomenon, recently named “instant warm seclusion,” is discussed in a new paper by graduate student Giorgio Sarro (now at the University of Chicago) and Clark Evans (University of Wisconsin-Milwaukee), now in press at Monthly Weather Review (see tweet below).

A famous recent case of the instant-warm-seclusion process is Hurricane Sandy, which became “Superstorm Sandy” – a post-tropical cyclone – just as it reached the coast of New Jersey. “Sandy was a great example,” Evans wrote in a tweet on Wednesday.

Much like Sandy, the impacts of Fiona will be essentially those of a hurricane, even if its formal classification changes in the hours before landfall. For this reason, Environment Canada has issued a hurricane watch for large parts of Atlantic Canada. “This storm is shaping up to be a severe event for Atlantic Canada and eastern Quebec,” the agency said in a statement on Thursday morning. “Numerous weather models are quite consistent in their prediction of what we call a deep hybrid low pressure system, possessing both tropical and intense winter storm properties, with very heavy rainfall and severe winds….most regions will experience some hurricane force winds. These severe winds will begin impacting the region late Friday and will continue on Saturday. cyclones of this nature have produced structural damage to buildings.”

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Widespread rains of 3 to 6 inches (75-150 millimeters) are expected over Atlantic Canada, with a corridor of even heavier rain likely along the track of Fiona’s core. “Some districts have received large quantities of rain recently, and excessive runoff may exacerbate the flooding potential,” Environment Canada noted. Huge waves can also be expected over a broad stretch of coastline, perhaps topping 39 feet (12 meters) in eastern parts of the Gulf of St. Lawrence. A significant storm surge is likely near and just east of the landfall point, especially if landfall coincides with the Saturday-morning high tide.

Fiona’s center most likely will come ashore in eastern Nova Scotia on Saturday morning, putting tiny Sable Island and larger Cape Breton Island at highest risk of the worst impacts. This is a lower-population region than central Nova Scotia, where Hurricane Juan became the costliest hurricane in Canadian history. Juan made landfall near Halifax at category 2 strength with 100-mph sustained winds and wreaked some $200 million (USD 2003) in damage. NHC predicts post-tropical Fiona will be packing 90-mph sustained winds near its landfall on Saturday morning.

Fiona is already a large hurricane, and its wind field will expand even further as it approaches Canada. Even if Fiona’s top winds are not quite as strong as Juan’s, a large swath of Atlantic Canada could experience hurricane-strength winds. Fortunately, there is much less development on the south-facing coast of eastern Nova Scotia than in the Halifax area, and Cape Breton’s largest city, Sydney, is somewhat protected on the east coast of the island. Nevertheless, Fiona will be a large-scale, high-impact storm for Atlantic Canada.

Fiona’s greatest mark in meteorological history may be its central pressure, which is predicted by multiple operational models to be as low as 925-930 millibars at landfall. This reading would smash the all-time sea-level pressure record for Canada of 940.2 millibars, set in St. Anthony, Newfoundland and Labrador, on January 21, 1977. (Note that about 60% of the 51 members of the 6Z Thursday European model ensemble predicted a sub-940 mb pressure, but only a few members of the GFS model ensemble did so.) Such a feat would be even more remarkable given that the strongest storms this far north are typically in the cold season.

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Although Fiona’s central pressure at landfall could be on par with some of the stronger U.S. hurricanes ever recorded, the huge size of Fiona means that the pressure gradient driving the winds will be much broader. This effect diffuses the storm’s energy into winds that are not quite so strong but that cover a broader area. Fiona is not expected to arrive with an eyewall, which produces the corridor of particularly intense wind damage one might see in a strong hurricane. However, NHC is predicting that sustained winds up to hurricane strength will extend by as much as 100 miles from Fiona’s center around the time of landfall, and tropical-storm-force sustained winds (39 mph or stronger) may extend a startling 300 miles from the storm center. As a result, tree falls and power outages with Fiona may cover a particularly large area, especially in Nova Scotia.

Figure 1. Tracks of all category 2 and stronger hurricanes to make landfall in Canada since 1851. (Image credit: NOAA)

Category 2 hurricanes and ex-hurricanes hitting Canada are rare

The 11 a.m. EDT Thursday intensity forecast from NHC puts Fiona just inland over eastern Nova Scotia as an extratropical storm with 90 mph winds on Saturday morning. This forecast is just below category 2 strength, so ex-Fiona is not predicted to be among the seven hurricanes or ex-hurricanes that have hit Canada at category 2 strength. According to the NOAA Historical Hurricane Tracks website, five Category 2 or stronger hurricanes have made landfall in Canada since records began in 1851:

  • Hurricane Five of 1893, which hit Sable Island with 100 mph winds before hitting the Burin Peninsula of Newfoundland on August 18 as a cat 1 with 90 mph winds.
  • The 1927 Nova Scotia Hurricane, which hit Yarmouth, Nova Scotia, with 105 mph winds, killing at least 173 people on 23 ships that sank in the storm. Flood damage in Nova Scotia was severe.
  • Hurricane Ginny of 1963, which hit southwestern Nova Scotia with 105 mph winds.
  • Hurricane Michael of 2000, which hit Newfoundland with 100 mph winds. (Note that NOAA’s Hurricane Research Division does not list Michael as being a hurricane when it made landfall, so there is some debate about whether the storm was extratropical at landfall.)
  • Hurricane Juan of 2003, which took a worst-case track and hit Halifax, Nova Scotia with 100 mph winds, killing 8 and causing $200 million (2003 USD) in damage – Canada’s most expensive hurricane on record.

And two ex-hurricanes have hit Canada at category 2 or 3 strength:

  • Ex-Hurricane Luis of 1995, which hit southeastern Newfoundland at category 3 strength, with 120 mph winds. A 95-foot rogue wave triggered by Luis hit the ocean liner Queen Elizabeth 2 about 230 miles south of Newfoundland, and a nearby buoy measured a 98-foot-high wave at roughly the same time. These are among the highest waves ever observed in the open ocean.
  • Ex-Hurricane Helene of 1958, which hit eastern Nova Scotia at category 2 strength, with 100 mph winds. Ex-Helene caused considerable wind and flood damage to Nova Scotia and Newfoundland.
Figure 2. Visible satellite image of 98L at 1:10 p.m. EDT September 22, 2022. (Image credit: NOAA/RAMMB/Colorado State University)

Disturbance 98L: a dangerous threat for Caribbean and Gulf of Mexico

An innocuous-looking tropical wave named 98L, along the north coast of South America in the southeastern Caribbean, may not look like much today, but the top computer models foresee a dramatic future for the disturbance – as a tropical storm or hurricane that may affect the western Caribbean and/or Gulf of Mexico next week. The system was bringing gusty winds and heavy showers to the ABC Islands and to the north coast of South America on Thursday afternoon, as it headed west-northwest at 10-15 mph.

Satellite imagery and Curacao radar on Thursday afternoon showed 98L with a moderate amount of heavy thunderstorm activity slowly growing more organized. A broad surface circulation had formed, but there was no well-organized surface circulation. A Thursday morning pass from the ASCAT satellite (see Tweet below) revealed that 98L had developed westerly winds of 15-20 knots on the south side of its circulation center, which is typically the hallmark of a disturbance on its way to becoming a tropical depression.

The main impediment for development for 98L on Thursday was the presence of Hurricane Fiona so nearby: Upper-level outflow from Fiona was bringing strong upper-level winds out of the north-northeast over 98L, creating high wind shear of 25-30 knots. Otherwise, conditions were favorable for development, with warm sea surface temperatures of 29-30 degrees Celsius (84-86°F) and a moist atmosphere (a mid-level relative humidity of 70%).

Continued high wind shear from Fiona’s upper-level outflow is expected to impede development of 98L through Friday morning, and 98L’s close proximity to the coast of South America may also hinder it. Odds for development will rise by Friday afternoon, when Fiona will be approaching Canada, allowing wind shear over 98L to drop to the moderate range, 10-20 knots. On Saturday, 98L will be in the central Caribbean, where favorable conditions for development are expected: very warm water of 30 degrees Celsius (86°F) with a high heat content, moderate wind shear, excellent outflow channels aloft, and a moist atmosphere (a mid-level relative humidity of 75-80%). The entire northern half of the Caribbean has been free of tropical cyclones all season, so these untouched waters (running about 0.5 degrees Celsius or 0.9 degree Fahrenheit above average for late September) will be particularly ripe for supporting any well-organized cyclone with favorable atmospheric conditions.

Figure 3. Track forecasts out to six days for 98L from the 6Z Thursday, September 22, run of the European ensemble model. Individual forecasts of the 51 ensemble members are the lines color-coded by the wind speed in knots they predict for 98L; red colors correspond to a category 1 hurricane. The heavy black line is the ensemble mean forecast. The time in hours from the model initialization time are in grey text. (Image credit: weathernerds.org)

The Thursday morning runs of all three of the top models for tropical cyclone genesis – the GFS, European, and UKMET – showed 98L developing into a tropical depression by early next week at the latest, as did many of the GFS and European model ensemble forecasts. These models had the advantage of assimilating data from last night’s dropsonde mission over the southeastern Caribbean, performed by an Air Force hurricane hunter aircraft which dropped 31 of the probes.

Over the past couple of days, multiple cycles of the GFS and European operational and ensemble model runs have depicted a robust hurricane moving across the western Caribbean and toward the Gulf of Mexico by the middle of next week. This consensus is a sign of model confidence in favorable conditions and cannot be ignored; however, model unanimity is not the same thing as model skill. Any twist in development along the way could affect all of these model solutions.

The spread in model track solutions is huge, with impacts to Central America, Mexico’s Yucatan Peninsula, Jamaica, the Cayman Islands, Cuba, and the U.S. Gulf Coast all in play. At this time, it appears that the western Gulf Coast (Texas) is at relatively low risk. While this situation could change, climatology does favor Texas landfalls to occur more often in late August and early September than in late September. And the model that shows the most westerly solutions for 98L – the GFS model – appears to be having trouble with the storm.

It is certainly plausible to anticipate that 98L could turn northwest and enter the Gulf of Mexico next week, since a trough of low pressure capable of creating the proper steering currents is expected to move across the U.S. Such a track is common toward the later side of hurricane season (late September into October), as the jet stream begins to dip further south and pull tropical systems northward and across the Gulf. Any threat to the U.S. Gulf Coast would most likely be in the general range of 6 to 10 days from now, so there is plenty of time to monitor 98L’s evolution.

In its 2 p.m. EDT Thursday Tropical Weather Outlook, NHC gave 98L 2-day and 5-days development odds of 80% and 90%, respectively.

Tropical Storm Gaston nears the Azores in central Atlantic

Residents of the western Azores should follow the forecasts for Tropical Storm Gaston, but no other land areas will be threatened by this storm. As of 2 p.m. EDT Thursday, Gaston had top winds of 65 mph, and was headed east-northeast at 21 mph toward the Azores. Given an array of less-than-ideal conditions, Gaston will probably weaken, as it enters a region with higher wind shear and colder waters. Gaston is expected to become post-tropical by Saturday.

Two other waves to watch: 90L and 99L

A tropical wave (Invest 90L) that moved off the west coast of Africa on Thursday has good model support for development through Saturday. The wave is expected to move on a somewhat unusual north-northwest track between the Cabo Verde Islands and the coast of Africa, and likely become post-tropical near the western Canary Islands by Sunday or Monday, in a region with cool waters, high wind shear, and dry air. This wave could bring rains of 2 -4 inches to the western Canary Islands Sunday through Monday. In its 8 a.m. EDT Thursday Tropical Weather Outlook, NHC gave this wave 2-day and 5-day development odds of 60%.

Only a handful of tropical cyclones have made it within 200 miles of the Canary Islands, including Delta in 2005 and Theta in 2020; none of these storms have been over or south of the islands themselves.

A tropical wave in the central Atlantic, several hundred miles west-southwest of the Cabo Verde Islands, was designated Invest 99L by NHC. The wave is in a dry environment (mid-level relative humidity of 50%), but sea surface temperatures are warm and wind shear is moderate, which could allow some slow development. Satellite imagery showed that 99L had developed a broad surface circulation, but had a very limited amount of heavy thunderstorm activity. The wave has only limited model support for development as it moves northwest at 5 mph, far from any land areas. In its 8 a.m. EDT Thursday Tropical Weather Outlook, NHC gave 99L 2-day and 5-day development odds of 20% and 30%, respectively.

The next two names on the Atlantic list of storms are Hermine and Ian.

Please donate to help hurricane victims

To help out with Fiona recovery efforts in Puerto Rico, please join us in donating to one of these worthy causes:

The Partnership for Inclusive Disaster Strategies (Formerly Portlight.org), helping disabled people in Puerto Rico recover from the hurricane.

The Fiona Community Response Fund, a coalition of community-led organizations working on immediate response to fulfill needs over the short- and long-term.

Red Cross


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Daniel Husband
Daniel Husbandhttps://petnews2day.com
I'm the editor for Pet News 2Day. I also a dog groomer for almost 5 years plus work along side my wife with her dog walking business too so I really understand the pet industry.

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