Tropical Storm Fiona is forming and will soon hit the Lesser Antilles and Puerto Rico
Tropical storm warnings have been issued for the northern Leeward Islands – including Saba and St Eustatius, St Maarten, Antigua, Barbuda, St Kitts, Nevis, Montserrat and Anguilla – and could be extended to Puerto Rico and the US Virgin Islands by Thursday afternoon or evening. Existing watches will likely be upgraded to warnings as the 50mph storm turns due west at 13mph.
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Winds up to tropical storm force will likely arrive beginning Friday evening and will be accompanied by heavy rains in the range of 3 to 6 inches. After passing near or over Puerto Rico, Fiona seeks to curve north, in which case a puzzle of uncertain atmospheric ingredients will play a west versus east tussle to determine where it ultimately goes.
Fiona is the sixth named storm in what has been a relatively quiet Atlantic hurricane season so far. The Atlantic Basin is operating at around 47.4% of average for ACE, or accumulated cyclonic energy – a measure of overall storm activity.
According to hurricane researcher Philip Klotzbach, this is the slowest start to the season since 2014, defying expert predictions of a particularly active 2022 season. By comparison, the hyperactive 2021 season had already unleashed 20 named storms and was about to plunge into the Greek alphabet.
At 8 a.m. EST on Thursday, the center of Fiona was located about 545 miles east of the Leeward Islands and was moving west at a typical pace. This westward movement is expected to continue through Friday when Fiona will impact the islands and Puerto Rico.
Maximum sustained winds were estimated at 50 mph, and the National Hurricane Center predicts subtle strengthening to a 55 mph storm. Thereafter, a plateau of intensity is expected continuing westward. The agency has asked ships within 300 miles of the storm’s position to record and submit weather observations every three hours, which will aid forecasting and modeling efforts. An Air Force Hurricane Hunter aircraft will be dispatched to investigate the storm later Thursday.
In infrared satellite imagery, Fiona is full of deep convection, or shower and thunderstorm activity. This is highlighted by the darker reds and whites, indicative of cold high clouds. But the majority of the storm is being moved to the east of its low-level circulation – notice in white the low-level cloud field rolling towards the center, which is obscured by higher clouds at ballast.
This lack of vertical system alignment is the result of west to northwest wind shear, or a change in wind speed and/or direction with altitude. This destabilizes the system and until it is able to better stack vertically, Fiona will have a hard time stepping up. A strengthening is not really expected in the short term, as the shear does not seem to relax anytime soon.
Eventually, the low-level center may stretch if a thunderstorm and its associated updraft pass over said vortex, but it remains to be seen if this will happen before arriving in Puerto Rico.
Fiona is expected to impact the northern Leeward Islands from Friday evening, with its core expected to cross the archipelago early Saturday. General rain of 3 to 6 inches, with a possibility of locally higher amounts, is expected. Gusty gusts with winds approaching 50-60 mph are also likely, along with dangerous coastal rip currents.
From there, the US model (GFS) suggests that Fiona could follow northern Puerto Rico while sweeping the northeastern fringe of US territory.
Conversely, the European model simulates a track south of Puerto Rico and possibly into Hispaniola. This could shred the storm’s circulation before it emerges over southeastern Bahamian waters. Torrential downpours from the storm over the Dominican Republic and Haiti could well lead to flooding and landslides, especially in mountainous areas where there is potential for double-digit rainfall.
The Hurricane Center’s forecast for Fiona’s path splits the difference between the US and European models, calling for a path over Puerto Rico before Fiona sails into the Mona Passage to the west of the island and to east of Hispaniola as it begins to curve north. The ultimate wild card, and therefore the different track scenarios, is when this right turn to the north will take place, which depends on the strength and position of the anticyclone to the northeast. This top acts as a bodyguard.
Ultimately, Fiona will be headed north, where, if she escapes earth and her inner core remains intact, she could begin to escalate within the next five to seven days.
Some computer model simulations predict it will pass ominously close to the east coast, deflected westward by the Bermuda High and pulled further inshore as it approaches low pressure seeking to capture it. Other models allow it to escape at sea, which would pose a greater risk to Bermuda. All in all, it’s just too early to tell, but it’s one you’ll want to keep a close eye on.