Tropical storm warnings have been hoisted in the northern Leeward Islands — including Saba and St. Eustatius, St. Maarten, Antigua, Barbuda, St. Kitts, Nevis, Montserrat and Anguilla — and could be expanded into Puerto Rico and the U.S. Virgin Islands by Thursday afternoon or evening. Existing watches will probably be upgraded to warnings as the 50 mph storm churns due west at 14 mph.
Winds up to tropical storm force will probably get there beginning Friday night and will accompany heavy rainfall on the order of 3 to 6 inches. After passing near or over Puerto Rico, Fiona looks to curve northward, at which point a jigsaw puzzle of uncertain atmospheric ingredients will play a west-vs.-east tug of war to determine where it ultimately goes.
Fiona is the sixth named storm of what, until now, has been a relatively quiet Atlantic hurricane season. The Atlantic basin is running at about 47.4 percent of average for ACE, or accumulated cyclone energy — a measure of overall storm activity.
According to hurricane researcher Philip Klotzbach, it’s the slowest start to a season since 2014, defying expert predictions of a particularly active 2022 season. By comparison, the hyperactive season of 2021 had already cranked out 20 named storms and was on the verge of dipping into the Greek alphabet.
As of 11 a.m. Eastern time Thursday, the center of Fiona was located about 495 miles east of the Leeward Islands and was moving west at a typical pace. That westward motion is expected to continue through Friday, when Fiona will deliver impacts to the islands and Puerto Rico.
Maximum sustained winds were estimated at 50 mph, and the National Hurricane Center anticipates subtle strengthening to a 55 mph storm. Thereafter, a plateau in intensity is expected as it continues west. 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 in forecasting and modeling efforts. An Air Force Hurricane Hunter plane will be dispatched to investigate the storm later Thursday.
On infrared satellite imagery, Fiona is replete with deep convection, or shower and thunderstorm activity. That’s evidenced by the darker reds and whites, indicative of high, cold cloud tops. But the majority of the storminess is displaced to the east of its low-level circulation — notice in white the low-level cloud field spiraling into the center, which is obscured by higher clouds to the east.
That lack of vertical alignment of the system is the result of westerly to northwesterly wind shear, or a change of wind speed and/or direction with altitude. It knocks the system off-kilter, and until it’s able to better stack itself vertically, Fiona will struggle to intensify. Strengthening isn’t really expected in the near-term, as shear doesn’t look to relax any time soon.
Eventually, the low-level center may become stretched if a thunderstorm and its associated updraft pass over said vortex, but whether that will happen before arrival in Puerto Rico remains to be seen.
Fiona is expected to bring impacts to the northern Leeward Islands beginning late Friday, and its core should cross the archipelago sometime early Saturday. A general 3 to 6 inches of rain, with a chance of locally higher amounts, is expected. Gusty squalls with winds approaching 50 to 60 mph are likely as well, along with dangerous coastal rip currents.
From there, the American (GFS) model hints that Fiona could…
Read More: Tropical Storm Fiona forms, soon to lash Lesser Antilles, Puerto Rico
