Tropical Storm Fiona forms, heading towards Puerto Rico’s Lesser Antilles

Tropical Storm Fiona formed hundreds of miles east of the Lesser Antilles late Wednesday and will bring heavy rain, rough surf, coastal rapids and strong wind gusts to the Leeward Islands and Puerto Rico. This is only what looks like the first act of a long journey to the western Atlantic, and there are growing signs that Fiona could end up being a hurricane and possibly a hurricane to watch in Bermuda or the US East Coast.

A tropical storm warning has been issued for the northern Leeward Islands, including Saba and St. Petersburg. Eustatius, St. Maarten, Antigua, Barbuda, St. Kitts, Nevis, Montserrat and Anguilla – and could expand to Puerto Rico and the U.S. Virgin Islands by Thursday afternoon or evening. Existing watches may be upgraded to a warning as the 50 mph storm is moving west at 14 mph.

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Tropical storm-strength winds are likely to reach there starting Friday night, along with about 3 to 6 inches of heavy rain. After passing near or over Puerto Rico, Fiona appears to be bending north, as a jigsaw puzzle of uncertain atmospheric composition engages in an east-west tug of war to determine where it ultimately goes.

Fiona is the sixth named storm, and the Atlantic hurricane season has been relatively quiet so far. The Atlantic Basin’s ACE averaged about 47.4 percent, or accumulated cyclone energy — a measure of overall storm activity.

According to hurricane researcher Philip Klotzbach, it was the slowest start to the season since 2014, bucking experts’ predictions for a particularly active 2022 season. By contrast, the 2021 hyperactive season has already produced 20 named storms and is on the verge of entering the Greek alphabet.

As of 11 a.m. ET Thursday, the center of Fiona was about 495 miles east of the Leeward Islands and was moving west at typical speeds. This westward movement is expected to continue through Friday, when Fiona will have an impact on the islands and Puerto Rico.

Maximum sustained winds are estimated at 50 mph, and the National Hurricane Center expects the storm to intensify slightly to 55 mph. After that, a plateau is expected in intensity as it continues westward. The agency has required ships within 300 miles of the storm’s location to record and submit weather observations every three hours, which will aid in forecasting and modeling efforts. Later Thursday, an Air Force Hurricane Hunter aircraft will be dispatched to investigate the storm.

On infrared satellite images, Fiona is full of deep convection, or showers and thunderstorm activity. This is evidenced by the darker reds and whites, indicating that the cloud tops are high and cold. But most of the storm shifted to the east of its low-level circulation—note the white low-level cloud field spiraling into the center, obscured by higher clouds to the east.

The lack of vertical alignment of the system is the result of westerly to northwesterly shear or changes in wind speed and/or direction with height. It throws the system off balance and Fiona will struggle to strengthen until it can stack vertically better. A strengthening isn’t really expected in the short term, as the shear isn’t going to loosen up anytime soon.

Ultimately, if the thunderstorm and its associated updraft pass through the vortex, the lower-level center could become tense, but it remains to be seen whether this will happen before reaching Puerto Rico.

Fiona is expected to make an impact on the northern Leeward Islands from late Friday, and its core should cross the islands sometime early Saturday. Typically 3 to 6 inches of rain is expected, with higher localized levels possible. Winds approaching 50 to 60 mph and dangerous coastal rip currents are also likely.

From there, the United States (GFS) model suggested that Fiona could track north of Puerto Rico while still sweeping across the northeastern edge of U.S. territory.

Instead, the European model simulates the orbit south of Puerto Rico and eventually into Hispaniola. This could disrupt the storm’s circulation before emerging in the waters of the southeastern Bahamas. The storm’s downpours over the Dominican Republic and Haiti are likely to cause flooding and landslides, especially in mountainous areas where double-digit rainfall totals are likely.

The Hurricane Center’s forecast for Fiona’s track distinguishes the difference between the U.S. and European models, calling for Fiona in Puerto Rico before Fiona begins to curve northward through the Mona Strait, west of the island and east of Hispaniola. Open a path in the sky. The final wild card, and different track scenarios, is when to turn north right, depending on the strength and location of the northeast high pressure. This height acts like a guardrail.

Eventually, Fiona will be directed north, and if it avoids land and its core remains intact, it could begin to intensify over the next five to seven days.

Some computer model simulations predict that it will pass ominously near the east coast, be diverted westward by the Bermuda High, and steer it further along the coast by approaching low pressure trying to capture it. Other models allow it to escape the sea, which would pose a greater risk to Bermuda. All in all, it’s too early to tell – but it’s something you’ll want to keep an eye on.

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