Implacable Hurricane Larry continues to lumber to the northwest at 13 mph as a large and powerful hurricane over the open central Atlantic. At 11 a.m. EDT Wednesday, Larry, with top sustained winds of 110 mph, finally lost its major hurricane status, after having been a category 3 storm since 3Z Saturday (11 p.m. EDT Friday). 

Satellite images showed Larry with a large eye, thick eyewall, and virtually no outer spiral bands. These qualities are characteristic of a special type of hurricane referred to as “annular”. Such hurricanes tend to form when the surrounding atmosphere is dry, making it difficult for the storm to maintain far-flung spiral bands.

Warm waters and low wind shear will provide a supportive environment for Larry over the next two days, but upwelling of cool water, decreasing heat content in the ocean, and dry air are likely to gradually degrade the hurricane. Larry is expected to pass just east of Bermuda on Thursday morning, bringing one to two inches of rain and winds near tropical storm-force. In its 11 a.m. EDT Wednesday wind probability forecast, the National Hurricane Center (NHC) gave Bermuda a 26% chance of experiencing tropical storm-force winds of 39 mph or more from Larry, but no chance of hurricane-force winds. A Tropical Storm Warning is up for the island.

Larry’s large size and long duration at category 3 strength are making the hurricane a formidable wave machine, and the Caribbean islands, Bahamas, Bermuda, and Florida were experiencing its resulting large waves and dangerous rip currents on Wednesday morning. These conditions, spreading westward and northward, will affect much of the U.S. East Coast and Canadian Maritime Provinces by Wednesday evening.

A trough of low pressure passing to the north of the hurricane is predicted to turn Larry to the north on Thursday, taking the hurricane about 150 miles east of Bermuda late Thursday morning. The trough will then turn Larry more to the northeast, bringing it near or over southeastern Newfoundland, Canada, on Friday night or Saturday morning. At that time, Larry will likely be a category 1 hurricane and transitioning to a powerful extratropical storm. In its 11 a.m. EDT Wednesday wind probability forecast, the NHC gave Cape Race, Newfoundland, an 82% chance of experiencing tropical storm-force winds of 39 mph or more from Larry, and a 22% chance of hurricane-force winds.

Figure 1. GeoColor satellite image of 91L at 12:20 p.m. EDT Wednesday, September 8, 2021. (Image credit: RAMMB/CIRA/Colorado State University)

Disturbance 91L likely to bring rains of 1-3 inches to Southeast U.S

In the northeastern Gulf of Mexico, an area of disturbed weather designated 91L was growing more organized and moving northeastward at about 10-15 mph, bringing heavy rain showers to the northeast U.S. Gulf Coast and adjacent waters, as seen on satellite imagery and Tallahassee radar. Though waters are warm and the atmosphere moist, 91L was experiencing moderate wind shear of 10-20 knots from an upper-level trough of low pressure, interfering with development.

Steering currents are predicted to continue carrying 91L to the northeast this week, bringing the system inland over the Florida Panhandle on Wednesday night. Heavy rains of one to three inches from 91L will likely affect a swath from the Florida Panhandle to coastal South Carolina, Wednesday through Thursday. On Thursday, 91L is predicted to emerge into the Atlantic Ocean off the Southeast U.S. coast. 91L could then develop over the warm waters of the Gulf Stream as it moves to the east-northeast away from the Southeast U.S. coast. 91L does have some modest model support for development, and in its 8 a.m. EDT Wednesday Tropical Weather Outlook, the NHC gave the system two-day and five-day odds of development of 50%. The next name on the Atlantic list of storms is Mindy. No hurricane hunter missions are tasked for 91L.

Two other areas to watch this weekend

This weekend may also be a time to watch for development of a new tropical wave expected to move off the coast of Africa on Friday or Saturday. In its 8 a.m. EDT Wednesday Tropical Weather Outlook, the NHC gave the new wave 2-day and 5-day odds of development of 0% and 20%, respectively.

The southwestern Gulf of Mexico’s Bay of Campeche will be another area for possible tropical cyclone formation this weekend, when a tropical wave may enter the Gulf and begin to develop, according to some of the ensemble members of the 6Z Wednesday run of the GFS model.

Super Typhoon Chanthu hits Cat 5

In the remarkably short time of 48 hours since it become a tropical depression, Typhoon Chanthu in the Northwest Pacific underwent extreme rapid intensification, topping out as a category 5 super typhoon with 160 mph winds at 5 a.m. EDT Wednesday in the waters east of the Philippines. Chanthu is a very small storm, and small tropical cyclones are capable of very rapid intensity changes, both strengthening and weakening. At its peak, Chanthu featured a tiny “pinhole” eye about four to six miles in diameter.

After hitting Cat 5 strength, Chanthu weakened slightly. It is likely that the inner eyewall collapsed and was replaced by a larger-diameter eyewall, a process known as an eyewall replacement cycle, common in intense tropical cyclones. At 11 a.m. EDT Wednesday, the Joint Typhoon Warning center (JTWC) said Chanthu was a category 4 super typhoon with 155 mph winds, heading west at 12 mph. On Friday, Chanthu is predicted to pass just north of the Philippines’ main island of Luzon as a dangerous category 4 storm, then gradually weaken before making landfall in China on Sunday.

Earth has had four category 5 storms so far in 2021:

Super Typhoon Chanthu in the Northwest Pacific near the Philippines (160 mph winds, September 8);
Super Typhoon Surigae in the Northwest Pacific near the Philippines (190 mph winds, April 17); (Editor’s note: This was corrected to 190 mph from the 180 in the original post)
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 NOAA’s National Hurricane Center and the U.S. Navy’s Joint Typhoon Warning Center. 

Figure 2. Barges battered by Hurricane Ida as seen on August 30, 2021. (Image credit: Congressman Garret Graves)

Mississippi River reopens; Port of South Louisiana remains closed

The Lower Mississippi River reopened to shipping on September 4, after being closed for navigation for a week after the impact of Hurricane Ida. According to Reuters, numerous barges and boats were sunk in the lower Mississippi River by Ida, and other debris has obstructed the navigation channel. These hazards are forcing daylight-only shipping in just the center of the river on a stretch from New Orleans upriver, with other restrictions.

Shipping is far from back to normal, with the country’s leading grain shipping port, the Port of South Louisiana, still closed and without power after being pounded by Ida when it was at category 3 strength with 115-120 mph winds. The port moved about 65% of the country’s soybean exports and 55% of corn exports in 2020. The September 2 port status report said it would be “some time” before the port would be fully operational, with no update since then.

That notwithstanding, U.S. Agriculture Secretary Tom Vilsack said on Wednesday that despite damages from Ida, the USDA does not expect them to “significantly curtail our capacity to export” grains. It is fortunate that Ida did not hit in October, during the peak grain export period, or the impact on exports would have been far more severe.

Power restoration progressing

According to the U.S. Department of Energy, 378,000 customers in Louisiana remained without power on Wednesday morning, down from the just over one-million customers who were without power at the height of Ida’s power outages on August 30. The hardest-hit areas, like Barataria in Jefferson Parish (see Tweet below), may not have their power restored until September 29.

Five oil refineries in Louisiana remained shut on Wednesday due to Ida, accounting for about 6% of the total U.S. refining capacity. On September 7, 79% of the oil production and 78% of the natural gas production in the federally administered areas of the U.S. Gulf of Mexico remained shut-in, according to estimates by the Bureau of Safety and Environmental Enforcement.

Toxic aftermath of Ida just beginning to be understood

Given Ida’s category 4 intensity at landfall and the large number of oil industry and other heavy industrial sites the hurricane impacted, it should be expected that the number of spills of oil and toxic substances released into the environment will be among the highest on record for a hurricane. The Washington Post reported on Tuesday night that over 2,000 spills of chemicals or oil occurred from Ida (see Tweet below).

Bob Henson contributed to this post.

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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...