Hurricane Fiona overcame the dry air and wind shear that had been stifling it to become the third hurricane of this year’s Atlantic season on Sunday in the waters just south of Puerto Rico. As of 11 a.m. EDT on Sunday, September 18, Fiona was packing top sustained winds of 80 mph and moving west-northwest at 8 mph, about 50 miles south of Ponce, Puerto Rico.

Fiona is a relatively large hurricane, so winds close to hurricane strength were already affecting Puerto Rico at midday Sunday. Sustained winds of 62 mph, gusting to 75 mph, were reported at Las Mareas on the southeast coast.

As Fiona clips the western end of Puerto Rico on Sunday afternoon and evening, it will put the island squarely on its stronger right-hand side, heightening the risks of wind and water. Much of the island can expect at least tropical storm-force winds sustained at 40 to 60 mph, enough to bring down trees and power lines. Puerto Rico is in a fraught multiyear process of upgrading its electrical grid, which remains compromised after the devastating impacts of Hurricane Maria in 2017 and a sequence of earthquakes in western Puerto Rico in late 2019 and early 2020. The lights went out on Saturday during a Fiona briefing from the governor, an unsettling harbinger of the power issues that could face many residents post-Fiona. As of 1 pm. EDT Sunday, reported that about 40% of the island’s customers were without power. UPDATE: Shortly after 1 p.m. an island-wide power outage hit Puerto Rico.

Flash floods and mudslides are the biggest immediate threat from Fiona. Because of Fiona’s relatively slow forward speed of 8 mph, rainfall totals of 10 to 20 inches will be widespread across Puerto Rico, and localized totals could top 25 inches where Fiona’s strong southerly winds hit the mountainous terrain. The wind threat is less across the eastern Dominican Republic, but rainbands on the west side of Fiona could bring pockets of 4 to 12 inches there.

Fiona’s rains have already caused havoc in the Leeward Islands; St. Claude Matouba Irfa, in the mountains in southwestern Guadeloupe, measured a 24-hour rainfall total of 19.85 inches (504.2 mm) on Saturday. One death on Guadeloupe is being blamed on flooding from Fiona.

Forecast for Fiona

The track forecast for Fiona is much more straightforward now that the hurricane has consolidated. Fiona will undergo a classic recurvature over the next several days, first going through the Mona Passage between Hispaniola and Puerto Rico on a northwesterly track, and then arcing northward and northeastward over time. Forecast ensemble members overwhelmingly agree on the recurvature, allowing residents of the U.S. East Coast to breathe more easily.

People in Bermuda need to take Fiona quite seriously. From Monday into Tuesday, the arcing path of Fiona will take it over an area of very warm sea surface temperatures (SSTs) that are 29-30 degrees Celsius (84-86°F), or about 1.5 degrees Celsius (2.7°F), warmer than average. These warm waters extend to unusual depth with high heat content, as shown in Figure 1, preventing cold water from being upwelled to dent Fiona’s strength. Despite moderate wind shear of around 15 knots, and an atmosphere that is only moderately moist (mid-level relative humidity of around 60%), Fiona could intensify dramatically, as the environment will gradually moisten and the wind shear will be largely aligned with Fiona’s motion. The DTOPS intensification index from the 12Z Sunday SHIPS model predicted a 51% chance that will Fiona will gain 30 mph of sustained wind by Monday morning.

Ocean heat content levels for Fiona
Figure 1. Ocean Heat Content (OHC) levels on September 18, 2022, with the 5 a.m. EDT advisory positions for Hurricane Fiona overlaid (annotated with the time in hours of the forecast). Fiona will move through a region with high OHC values of 75 -100 kilojoules per square centimeter (orange colors) for the next three days. OHC values in excess of 75 are highly favorable for rapid intensification of hurricanes. (Image credit: RAMMB/CIRA/CSU)

The National Hurricane Center brings Fiona to category 3 strength (115 mph winds) by Wednesday, which would make it the season’s first major Atlantic hurricane. In a typical year (1991-2020), the third hurricane arrives on September 7, the first major hurricane is observed on September 1, and the seventh named storm (not yet observed this year) arrives on September 3, so the 2022 season continues to lag behind climatology.

Despite the high confidence in Fiona’s general recurvature, it’s too soon to know whether the track will pass east, west, or over Bermuda on Thursday night or Friday morning. That said, a direct hit is certainly possible. Fiona has the potential to produce the largest impacts in Bermuda since the western eyewall of Hurricane Nicole passed directly over the island in 2016 while Nicole was a category 3 storm.

Radar image of Nanmadol
Figure 2. Radar image of Typhoon Nanmadol near the time of landfall on Japan’s Kyushu Island, at the head of Kagoshima Bay. (Image credit: Japan Meteorological Agency)

Powerful Typhoon Nanmadol hits Japan

Typhoon Nanmadol made landfall on Japan’s Kyushu Island near 7 p.m. local time (8 a.m. EDT) Sunday, September 18, near the head of Kagoshima Bay. At landfall, the Joint Typhoon Warning Center (JTWC) rated Nanmadol a high-end category 2 storm with 110 mph winds (1-minute average); the Japan Meteorological Agency (JMA) put Nanmadol’s winds at 105 mph (10-minute average), with a central pressure of 935 mb. This pressure is tied for fourth-lowest of any typhoon to make landfall on mainland Japan in the JMA database, which extends back to 1951.

About an hour later, the eye of the powerful typhoon passed over Kagoshima City (population 600,000), but the storm did not take a worst-case track for a devastating storm surge to push up the narrow bay the city lies on, with the strongest winds in the right-front quadrant of the typhoon affecting the coast just east of the bay. The portion of the coast is relatively sparsely populated, and it is likely that storm surge damage from the typhoon will end up being less destructive than the damage from rain and wind.  

Extreme rainfall and damaging winds affecting Japan

Typhoon Nanmadol tapped into a spigot of intense tropical moisture, and the storm has dumped truly prodigious amounts of rain over Japan’s mountainous terrain. At least five stations on Kyushu Island recorded over a half-meter (19.69 inches) of rain in just 24 hours on Sunday. The highest amount was 694.5 mm (27.34”) at Mikado; the 48-hour rainfall at that station was 830 mm (32.68”). Rains of this magnitude are capable of causing devastating flash flooding and mudslides, and Nanmadol will likely cause billions in damage in flooding alone.

Precipitation levels for Nanmadol
Figure 3. Typhoon Nanmadol precipitation for the 24 hours ending at midnight Sunday (local time). The highest amount was 694.5 mm (27.34”) at Mikado. The 48-hour rainfall at that station was 830 mm (32.68”). (Image credit: JMA)

Wind damage will also be heavy. When the typhoon passed over Yakushima Island, located about 30 miles south of Nanmadol’s landfall point on Kyushu, the peak hourly sustained 10-minute average winds were 36.4 m/s (82 mph), with a wind gust of 50.9 m/s (114 mph). However, there were few high-end sustained wind reports from some of the airports in the path of Nanmadol’s eyewall on Kyushu. For example, the highest sustained winds at Kagoshima City were 18.7 m/s (42 mph), with a wind gust of 43.5 m/s (97 mph). Nevertheless, Nanmadol will subject a huge region of Japan to damaging winds. The 11 a.m. EDT Sunday advisory from JTWC rated Nanmadol as a high-end category 1 typhoon with 90 mph winds, with typhoon-strength winds that extended out up to 85 miles from the center. JTWC predicted that Nanmadol would maintain typhoon strength for an additional 12 hours, when it would be more than 150 miles from its initial landfall location in Kyushu. Nanmadol is expected to turn to the northeast and track directly up the Japanese main island of Honshu, bringing strong winds and torrential rains to a remarkably large area of Japan.

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Jeff Masters, Ph.D., worked as a hurricane scientist with the NOAA Hurricane Hunters from 1986-1990. After a near-fatal flight into category 5 Hurricane Hugo, he left the Hurricane Hunters to pursue a...

Bob Henson is a meteorologist and journalist based in Boulder, Colorado. He has written on weather and climate for the National Center for Atmospheric Research, Weather Underground, and many freelance...