The Atlantic was living up to the climatological peak of hurricane season on Friday, September 10. One long-lived hurricane was heading for an expected landfall in Canada, and two other systems are likely to develop by early next week.

Hurricane Larry was spinning across the Northwest Atlantic on Friday afternoon, holding at category 1 strength with top winds of 80 mph. At 2 p.m. EDT Friday, Larry was located about 465 miles southwest of Cape Race, Newfoundland, zipping to the north-northeast at 29 mph. In its ninth day as a hurricane, Larry is a sprawling system, with hurricane-force winds extending up to 90 miles from its center and tropical-storm-force winds extending up to 240 miles.

Figure 1. Visible satellite image of Hurricane Larry heading toward Newfoundland, Canada, at 1:27 p.m. EDT Friday, September 10, 2021. (Image credit: University of Wisconsin).

Strong convection (showers and thunderstorms) continued to spiral around Larry’s broad center, as the storm remained over sufficiently warm sea surface temperatures of around 27 degrees Celsius (81°F). Wind shear was light to moderate, around 10 knots. Dry air (mid-level relative humidity around 50%) lent some patchiness to Larry’s convective banding.

Strong, well-defined steering currents will turn Larry slightly toward the northeast, putting it on course late Friday evening to strike Newfoundland, the large island that makes up part of the Canadian province of Newfoundland and Labrador. Colder water and increased wind shear will hasten Larry’s conversion into a powerful extratropical cyclone, but Larry may still be classified as a category 1 hurricane when it reaches southeast Newfoundland, perhaps passing over or near the provincial capital and largest city, St. John’s. According to the Weather Company’s Jonathan Erdman, the last hurricane to make landfall in Newfoundland was Igor in 2010.

Figure 2. Tracks of all category 1 and stronger hurricanes to affect Newfoundland since 1851. (Image credit: NOAA)

Hurricanes hitting Newfoundland are uncommon; NOAA’s hurricane database shows 13 category 1 or stronger hurricanes have hit the island since 1851. Two of these were category 2 storms: Michael in 2000, and an unnamed 1893 storm. However, many other hurricanes not shown in the graphic above have passed over Newfoundland as hurricane-strength extratropical storms shortly after having lost their tropical characteristics.

After it exits Newfoundland, Larry will continue to be a major weathermaker, dumping several feet of snow in southeast Greenland as it spins just offshore with gale-force winds pushing onto the rugged terrain. Such hurricane-spawned snowfall can be a surprising factor in helping to maintain Greenland’s storehouse of ice against the challenges of a warming climate.

Mindy is no more

After just 31 hours as a tropical storm, Mindy was declared a post-tropical cyclone at 11 p.m. EDT Thursday, September 9, as it hurtled east-northeast well off the coast of South Carolina. Coastal flooding resulting from Mindy’s storm surge as it made landfall Wednesday evening on the Florida Panhandle was minor, with less than two feet of surge observed at tide gauges along the Florida Gulf Coast.

The heaviest two-day rainfall from Mindy occurred in the central Florida Panhandle and across coastal South Carolina. Peak amounts observed by CoCoRaHS volunteers as of Friday morning included 4.75 inches at Seabrook Island, SC, and 4.53 inches just north of Tallahassee.

Figure 3. Infrared satellite image of a tropical disturbance in the Northwest Caribbean at 1530Z (11:30 a.m. EDT) Friday, September 10, 2021. (Image credit: RAMMB/CIRA/CSU)

Two new Atlantic tropical cyclones expected to form

Two tropical waves were showing increased potential for development on Friday. The next two names on the Atlantic list are Nicholas and Odette. Both names have been used only once before, for tropical storms in 2003.

Closest to North America was a disturbance festering in the far Northwest Caribbean and adjacent parts of Central America and the Yucatan Peninsula. Convection remained disorganized on Friday, but as the system drifts northwest, it will encounter an existing low-pressure system in the Bay of Campeche over the weekend. The most likely outcome is for a tropical depression to develop, perhaps strengthening into a tropical storm before continuing northwest to north-northwest and striking the coast of northeast Mexico or southern Texas early next week. In its 2 p.m. EDT Friday Tropical Weather Outlook, the National Hurricane Center gave this system 2-day and 5-day odds of development of 40% and 70%, respectively. A hurricane hunter aircraft is scheduled to investigate this area on Sunday afternoon.

The probable main impact would be rain of two to four inches along the coast of the western Gulf of Mexico, perhaps extending northward to the upper Texas and Louisiana coasts as the system pulls a slug of very moist air onshore toward its north end. Localized coastal rains could be heavier as the week unfolds, and NOAA is predicting 7-day rainfall amounts could total over seven inches for much of the Texas coast and southwest Louisiana coast.

Figure 4. Probability of a tropical depression forming between 8 p.m. EDT Saturday, September 11, and 8 p.m. EDT Monday, September 13, based on the 0Z Thursday ensemble output of the European forecast model. (Image credit: weathermodels.com)

Another system worth watching was moving off the coast of Africa on Friday evening and heading west-northwest into the eastern tropical Atlantic. This disturbance likely will affect the Cabo Verde Islands on Saturday night and Sunday, and intensify further as it moves away from Africa. Long-range model ensembles strongly support eventual development of this system. In its 2 p.m. EDT Friday Tropical Weather Outlook, the National Hurricane Center gave this system 2-day and 5-day odds of development of 50% and 70%, respectively. This system will be a relatively slow mover, so plenty of time remains to monitor its progress further into the Atlantic.

Figure 5. Infrared satellite image of a tropical disturbance emerging from the coast of Africa at 1530Z (11:30 a.m. EDT) Friday, September 10, 2021. (Image credit: RAMMB/CIRA/CSU)

Category 5 super typhoon Chanthu headed toward Taiwan

After rapidly intensifying to a category 5 storm with 160 mph winds on Wednesday in the Northwest Pacific east of the Philippines, Typhoon Chanthu has undergone some fluctuations in strength, weakening to a Cat 4 with 140 mph winds on Thursday, then restrengthening to 165 mph winds early Friday. These fluctuations were likely the result of eyewall replacement cycles – a process whereby the inner eyewall collapses and is replaced by a larger-diameter eyewall, common in intense tropical cyclones. Chanthu is a very small storm, and small tropical cyclones are capable of very rapid intensity changes, both strengthening and weakening.

At 11 a.m. EDT Friday, the Joint Typhoon Warning Center (JTWC) rated Chanthu a category 5 super typhoon with top winds of 160 mph, headed northwest at 12 mph; the Japan Meteorological Agency (JMA) assigned Chanthu a central pressure of 905 mb. Chanthu skirted the northeast coast of the Philippines’ Luzon Island on Friday morning, but was on track to hit the Philippines’ tiny Babuyan Island (population 1,400), with its western eyewall.

Forecast for Chanthu

Chanthu is in an environment supportive for typhoons, with sea surface temperatures of 29-30 degrees Celsius (84-86°F), light wind shear, and a moist atmosphere. The predicted track from JTWC and JMA will bring Chanthu perilously close to Taiwan on Saturday, when the core of the typhoon likely will pass over northern Taiwan or just offshore to the east. Chanthu likely will be at category 4 strength at that time, and capable of causing devastating damage. As Chanthu moves north, its most dangerous side will be on the east (the right-hand side), so a track just offshore could reduce the wind threat, but torrential rains and mudslides would remain a major concern. After Chanthu passes Taiwan, steering currents likely will take it to the north, with a potential threat to eastern China by early next week.

Chanthu is Earth’s second-strongest tropical cyclone of 2021, and is one of four category 5 storms so far this year:

Super Typhoon Chanthu in the Northwest Pacific near the Philippines (165 mph winds, September 8);
Super Typhoon Surigae in the Northwest Pacific near the Philippines (190 mph winds, April 17);
Tropical Cyclone Faraji in the southwest Indian Ocean (160 mph winds, February 8); and
Tropical Cyclone Niran in the South Pacific Ocean (160 mph winds, March 5).

Earth averaged 5.3 category 5 storms per year between 1990 and 2020, according to ratings made by the NHC and the U.S. Navy’s Joint Typhoon Warning Center. 

Category 2 Olaf hits Mexico’s Baja Peninsula

In the Eastern Pacific, Hurricane Olaf put on an impressive display of rapid intensification Thursday, going from a tropical storm with 50 mph winds to a category 2 hurricane with 100 mph winds in the 24 hours before making landfall on the southern tip of Mexico’s Baja Peninsula at 11 p.m. EDT Thursday, September 9. Olaf is the strongest hurricane to hit the southern tip of Baja since category 3 Hurricane Odile of 2014, which killed 18 and did $1.3 billion in damage.

Interaction with the Baja Peninsula’s rugged terrain  weakened Olaf, and at 11 a.m. EDT Friday, Olaf was a tropical storm with 70 mph winds, headed northwest at 10 mph, just offshore of Baja. Steering currents are expected to carry Olaf to the west, away from Baja, by Friday night, as the storm rapidly weakens.

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Jeff Masters

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

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...