Climatology

Puerto Rico crippled by flash flooding and power failures as Fiona heads toward Bermuda » Yale Climate Connections

Hurricane Fiona made landfall on the southwestern corner of Puerto Rico at 3:20 pm EDT Sunday as a category 1 storm with 85 mph winds. Although Fiona arrived as “only” a Cat 1, the impacts from Fiona’s rains have been catastrophic – characteristic of a major hurricane – with widespread rainfall amounts of 1-2 feet causing devastating flooding.

Challenging and 24-hour rainfall record

Multiple locations in Puerto Rico recorded more than 20 inches of rain in the 24 hours ending at midnight Sunday. According to the National Weather Service, the Puerto Rico record for 24-hour rainfall is 23.75 inches, set at Toro Negro Forest on October 7, 1985, during the passage of a tropical wave that later became Tropical Storm Isabel. The National Weather Service reported that Fiona brought 22.00 inches during the calendar day Sunday to a COOP site (Adjuntas). Rain gauges near Ponce reported 21.09 inches and near Caguas reported 20.62 inches respectively.

The Caguas rain gauge recorded an astonishing 27.14 inches of rain in the 24 hours ending at 10:15 am EDT Monday, which if confirmed would set a new 24-hour rainfall record for Puerto Rico.

As of 11 am EDT Monday, the National Weather Service reported that three rivers in Puerto Rico were at major flood stage, and at least 10 rivers have been at major flood since Sunday, with several exceeding their all-time record water levels set in 2017 during Hurricane Maria.

While rain has been the main story with Fiona, the hurricane also brought high winds that caused significant tree and power line damage. Winds gusted as high as 103 mph at the Ponce Yacht and Fishing Club shortly before 2 pm EDT Sunday, and to 113 mph inland at higher elevations at Yauco in southwestern Puerto Rico.

Arriving on top of ongoing problems with Puerto Rico’s power grid, Fiona’s winds and flooding were likely responsible for an island-wide power outage that began near 1 pm EDT Sunday. As of 10 am EDT Monday, poweroutage.us was reporting that 90% of the island was still without power. Since wind damage will be less with Fiona than with Maria, power in larger cities may be restored more quickly this time, but prolonged outages are still quite possible, especially in remote areas where flooding will make access difficult. Approximately 25% of the island’s population was also without wateras of 8 am EDT Monday.

Severe flooding in the Dominican Republic

Overnight, Fiona jogged westward through the Mona Passage between Puerto Rico and the Dominican Republic, strengthening to a 90-mph hurricane before making landfall at 3:30 am EDT Monday about 20 miles south-southwest of Punta Cana in the Dominican Republic. Torrential rains from Fiona began affecting the eastern portion of the Dominican Republic on Sunday night and continued into Monday afternoon, causing damaging flooding (see Tweet below from the town of Higüey).

As of 11 am EDT Monday, Fiona was moving back offshore along the northeastern coast of the Dominican Republic. The hurricane’s strength was dented only slightly during its overland trek, as top sustained winds were still at 85 mph. Even more concerning, Fiona’s sprawling circulation continued to pull heavy rain bands northward into Puerto Rico at midday Monday. Rainfall totals of 8 to 16 inches from Sunday to Monday morning are widespread across the island, according to reports from CoCoRaHS and other sources.

Fiona expected to become 2022’s first major Atlantic hurricane

As Fiona moves away from the Caribbean and embarks on a classic recurving path, she will enter an environment very supportive of strengthening. Moderate wind shear of 15-20 knots will be largely aligned with Fiona’s motion, and the storm’s well-organized structure and very warm, moist low-level air should enable it to thrive despite a surrounding deep atmosphere that is only moderately moist (mid- level relative humidity of around 60 percent). Fiona will also benefit from very warm sea surface temperatures (SSTs) of 29-30 degrees Celsius (84-86°F), or about 1.5 degrees Celsius (2.7°F), warmer than average. Moreover, these warm waters extend to unusual depth with high heat content.

Two top operational intensity models, HWRF and HMON, agree with statistical guidance in calling for Fiona to rapidly intensify from Monday to Tuesday. The SHIPS DTOPS tool from 12Z Monday shows a 63% chance that Fiona will gain 35 mph of sustained wind by 12Z Tuesday, which would bring it to solid category 3 status (120 mph). HWRF and HMON likewise have Fiona becoming a major category 3 storm by midday Tuesday, and the National Hurricane Center (NHC) forecast calls for Fiona to be a major hurricane by 0Z Wednesday.

As of midday Monday, NHC does not explicitly predict Fiona to reach category 4 strength, and the storm may embark on eyewall replacement cycles around midweek that keep it from intensifying further, but both HWRF and HMON suggest that periods of category 4 strength are quite possible . The new HAFS model agrees.

There is high confidence in Fiona’s general recurving path, keeping the hurricane well east of North America but carrying it close to Bermuda late Thursday or early Friday. Despite the high overall confidence, it’s still too soon to know for sure whether Fiona might pass west, east, or over Bermuda.

The latest guidance is leaning towards a path just west of Bermuda, but potentially close enough to bring damaging wind from the hurricane’s stronger right-hand side to the island. That said, a direct hit is not yet out of the question. Given the unusually warm waters ahead of Fiona, this hurricane 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.

Figure 2. Track forecasts out to 10 days for Fiona from the 6Z Monday, September 19, run of the GFS ensemble model. Individual forecasts of the 31 ensemble members are the lines color-coded by the wind speed in knots they predict for Fiona; red colors correspond to a category 1 hurricane. The heavy black line is the ensemble mean forecast. The time in hours from the model initialization time are in gray text. (Image credit: weathernerds.org)

On Friday night or Saturday morning, Fiona is expected to reach Newfoundland, perhaps as a hurricane, but more likely as a potent, fast-moving post-tropical cyclone. In either case, Fiona will likely be near hurricane strength.

New threat approaching the Caribbean

A tropical wave about 700 miles west of the Windward Islands on Monday afternoon was headed west to west-northwest about 10-15 mph, and was producing a disorganized area of ​​heavy thunderstorms. The wave is predicted to pass through the Windwards and enter the Caribbean on Thursday. This wave, with support for development from the operational GFS model and a number of members of the GFS and European model ensemble forecasts, will need to be monitored for development later this week. In its 2 pm EDT Tropical Weather Outlook, NHC gave this system a 20% chance of development, mainly between Wednesday and Saturday.

Well to the north, in the central North Atlantic, another system could briefly take on tropical characteristics in the next couple of days but would pose no threat to land. This system has 2- and 5-day odds of development of 30%, implying that the odds are low beyond Wednesday.

The next name on the Atlantic list of storms is Gaston.

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