Fiona to bring life-threatening flood risk to Puerto Rico, Virgin Islands

Tropical Storm Fiona was closing in on the Leeward Islands Friday morning, and AccuWeather forecasters warned that the storm’s strong winds and heavy rains would begin impacting the northeastern Caribbean by Friday night. There is the potential for Fiona to become a hurricane after turning northward next week, and one scenario could bring the storm near the United States East Coast.

As of 8 a.m., Fiona, the sixth named storm of the season, was located about 175 miles east of Guadeloupe in the Leeward Islands and its maximum sustained winds remained at 50 mph after its winds reached 60 mph Thursday. Tropical-storm-force winds extend outward up to 125 miles, the National Hurricane Center said. The outer bands from Tropical Storm Fiona were nearly reaching some of the Leeward Islands Friday morning.

The tropical storm is the most significant tropical system to impact the Caribbean so far this Atlantic hurricane season, which has been unusually quiet, and meteorologists say although the storm is forecast to lose some intensity as it encounters the rugged mountainous terrain of some islands, it will still bring a substantial flood risk.

Tropical storm watches were in place for Puerto Rico and the U.S. and British Virgin Islands, and forecasters warned that those islands could get slammed with heavy rainfall amounts as high as 10 inches, which would pose a significant flood and mudslide risk.

Tropical storm watches were upgraded to warnings in parts of the Leeward Islands Thursday. The government of Antigua and Barbuda issued the warnings for Antigua, Barbuda, St. Kitts, Nevis, Montserrat and Anguilla, the NHC said. Elsewhere, the Netherlands government issued a warning for the islands of Saba and St. Eustatius, while the government of St. Maarten declared a warning as well.

Disruptive wind shear has been limiting Fiona’s strength since it formed Wednesday night, and Fiona will encounter another strength-limiting factor over the weekend as it drifts over the warm waters of the northeastern Caribbean.

After the storm passes the Lesser Antilles, its circulation will encounter 4,000-foot mountains on Puerto Rico and 10,000-foot mountains on Hispaniola. These high mountains will exert a drag on the system and allow dry air to mix into the storm’s circulation. Because of these conditions, Fiona is unlikely to gain much strength through this weekend and could trend weaker for a time.

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Winds are likely to remain within tropical storm force, between 40 and 60 mph, through this weekend. Most of the winds at this level will be in the form of gusts from locally heavy thunderstorms where an AccuWeather Local StormMax™ gust of 70 mph is possible. But, even at this level, there is the likelihood of power outages and minor property damage.

Despite Fiona’s moderate wind intensity, there is every indication that the tropical storm will pack enough moisture to bring torrential downpours across the island of the northeastern Caribbean, with the heaviest rain likely where the terrain is the most mountainous in Puerto Rico, the Dominican Republic and Haiti.

Non-flooding rainfall, although disruptive, can be beneficial where there have been few downpours this summer. However, a general 4-8 inches of rain is forecast to fall on much of Puerto Rico and the Dominican Republic with an AccuWeather Local StormMax™ of 18 inches. Rainfall of this magnitude will trigger life-threatening flash flooding and mudslides. Even 2-4 inches poised for the Virgin Islands and Haiti can lead to localized flooding and debris flows, forecasters warn.

Given an anticipated significant flooding threat with 8-12 inches of rain across portions of far western Puerto Rico and eastern Dominican Republic, AccuWeather forecasters have rated Fiona a 1 on the AccuWeather RealImpact™ Scale for Hurricanes.

The worst conditions in terms of torrential downpours and gusty winds will spread westward across the Lesser Antilles through Friday night and Saturday. The storm’s forward speed is likely to slow down, which will be another factor concerning the heavy rainfall.

Puerto Rico will feel the impacts of Fiona from Saturday through Sunday. From Sunday to Monday, Fiona will likely take a turn to the north and travel across Hispaniola and unleash flooding rain and gusty winds on the Dominican Republic and Haiti.

If the rugged mountains of Hispaniola do not completely tear up Fiona, the combination of warm water and a lower amount of wind shear could allow the storm to gain strength as it moves on a north-northwest path near the Bahamas early next week.

Where Fiona will track later next week and the following weekend will depend on the behavior of the jet stream. One scenario keeps a southward dip in the jet stream in place long enough to guide Fiona on a curved path over the western and northern Atlantic. This idea remains the leading potential long-term track.

A NOAA satellite image showed Tropical Storm Fiona churning over the Atlantic Ocean, moving westward toward the Caribbean Sea, on Friday, Sept. 16, 2022.

However, there is another scenario that has been gaining a bit in percentages over the past few days. In this possibility, the southward dip in the jet stream does not last long enough to keep Fiona at sea. Instead, the jet stream dip races away and a zone of light steering winds remains. This could allow Fiona to wander close to the Atlantic coast of the U.S. next weekend and beyond.

As a result, people in the Turks and Caicos, the Bahamas, Bermuda, the U.S. and Atlantic Canada should monitor Fiona’s progress, AccuWeather forecasters say.

So far the 2022 Atlantic hurricane season has paled in comparison to the previous two years. Last year at this point of the season, some 20 named storms had developed in the Atlantic basin. Though September 2022 has seen a relative flurry of tropical activity, there has not been a hurricane within striking distance of the U.S. mainland yet this season, and August was a historically inactive month, which went without a single named storm for the first time in 25 years.

Another metric meteorologists use to gauge the overall intensity of a hurricane season is ACE, or the accumulated cyclone energy of each named storm in a hurricane season. Given that there have been just six named storms this year, the 2022 ACE value, which stood at 31.1 as of Sept. 16, according to Colorado State University, was also dramatically trailing the pace of the 2021 Atlantic hurricane season, which finished with a value of 145.7.

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