On Monday, for just the second time on record, the Atlantic has five simultaneous hurricanes, tropical storms, and tropical depressions, as Hurricane Paulette, Hurricane Sally, Tropical Storm Teddy, Tropical Storm Vicky, and Tropical Depression Rene all roamed the waters.
Colorado State University hurricane scientist Phil Klotzbach says the only other time five simultaneous tropical cyclones existed in the Atlantic was September 11-14, 1971. The record is six, set during the period September 11-12, 1971: Edith, Fern, Ginger, Unnamed, Heidi and Irene.
Just four days after the climatological midpoint of the Atlantic hurricane season, we’ve had 20 named storms so far in 2020, an astounding level of activity. Only 2005 had more named storms during an entire season, with 28.
Sally intensifies into a dangerous hurricane
At 12:30 p.m. EDT Monday, September 14, Sally was centered 165 miles southeast of Biloxi, Mississippi. Sally was a strengthening hurricane with 90 mph winds, moving west-northwest at 7 mph with a central pressure of 985 mb. Wind gusts as high as 66 mph were observed late Monday morning at the VK 786/Petronius (Chevron) oil rig offshore from Mobile, Alabama (elevation 53 feet).
Sally was bringing heavy rains to the Florida Panhandle and to the Alabama coast on Monday. On Sunday, Sally brought more than five inches of heavy rains to portions of the Florida west coast, after deluging the Florida Keys on Saturday with 11.36 inches at Key West and 11.99 inches at Lower Matecumbe Key.
Satellite and radar images showed a sharp increase in the intensity of Sally’s heavy thunderstorm activity on Monday morning, with the surface center of circulation reforming to the east under the most intense thunderstorms, allowing the storm to become vertically aligned. Moderate wind shear of 10-20 knots from upper-level winds out of the west continued to interfere with heavy thunderstorm formation on the west side of Sally’s circulation. However, radar imagery showed Sally in the process of closing off an eyewall, and once that process is complete, the wind shear will have less of an impact and more rapid intensification can occur.
Satellite imagery late Monday morning appeared to show a pattern called a Central Cold Cover (CCC), with a single large thunderstorm dominant. Typically, the huge thunderstorm when a CCC pattern is present is anchored to the arm of a low-level rain band some distance outside of the storm’s core; in that case, development is typically slowed until the large thunderstorm goes away (kudos to Boris Konon and Mark Lander for pointing this out). Usually, a storm is at an intensity of about 55 – 65 mph when a CCC occurs, though a CCC can happen at any stage of development. It is possible that this CCC structure may be able to slow Sally’s intensification.
Forecast for Sally
The track forecast for Sally has more uncertainty than usual for a storm expected to make landfall in less than 48 hours. Sally is forecast to move in a general west-northwest motion at about 6 – 7 mph through Monday night. Steering currents will weaken by Monday night, causing a slowdown of Sally’s forward speed to 5 mph or less, as the storm begins to feel the influence of a strong band of upper-level west-southwesterly winds over the southern U.S.
A weakness in the ridge of high-pressure steering Sally should allow the storm to turn north by Tuesday morning, when Sally will be very close to the coast. The timing of this turn will strongly depend upon how quickly Sally organizes and intensifies. A stronger storm will be affected more by the upper-level winds, which are blowing from the west, forcing a quicker turn to the right and resulting in a landfall in Mississippi or Alabama. A slower-organizing storm is more likely to make landfall in Louisiana, at a lower intensity. With Sally now a hurricane, a turn more to the right and landfall in Mississippi or Alabama appears most likely.
Wind shear may decrease to around 10 knots by Monday night, which will potentially allow Sally to completely close off a center and finish building an eyewall. The air mass surrounding Sally is reasonably moist, with a mid-level relative humidity around 65%, so dry air is unlikely to be a major hindrance to this process.
By Tuesday morning, wind shear is expected to tick up a notch, to around 20 – 25 knots, which may slow or halt the intensification process. This shear will be caused by the strong band of upper-level westerly winds helping steer Sally more to the right, as mentioned above. This band of winds will also ventilate Sally, though, providing an upper-level outflow channel capable of aiding intensification.
Sally will be over the very warm waters of the northeastern Gulf of Mexico, where sea surface temperatures are around 29.5°C (85°F). There is plenty of heat energy in the ocean waters Sally will be traversing to support rapid intensification, as the storm should remain just northeast of a cool eddy with low oceanic heat content over the southeast Gulf.
How much Sally strengthens will depend in large part on how quickly it closes off an eye; a period of rapid intensification cannot be ruled out if the storm organizes quickly enough. The 12Z Monday run of the SHIPS model gave a 16% chance that Sally would rapidly intensify by 30 mph in a 24-hour period, and an 11% chance it would intensify by 50 mph in 36 hours. Sally was just shy of meeting that 16% chance of intensifying 30 mph in 24 hours, since it intensified by 25 mph between 8 a.m. and 12:30 p.m. EDT Monday.
The official forecast calls for Sally to peak as a category 2 hurricane with winds of 105 mph, but it could reach category 3 hurricane strength with 115 mph winds if it manages to close off a complete eyewall by Tuesday morning.
Rainfall and storm surge: two major concerns with Sally
Regardless of its landfall intensity, the primary damage from Sally is likely to result from the slow-moving storm’s torrential rains. Sally is expected to move at 6 mph or less through Thursday, leading to rainfall measurements in feet rather than in inches. Models suggest that localized totals in excess of two feet are possible. A larger corridor of 8-16 inches can be expected near the coasts of southeast Louisiana, Mississippi, Alabama, and the extreme western Florida Panhandle.
Storm surge is also a major concern, with up to 11 feet of surge predicted along the east side of New Orleans. As discussed in Sunday’s post, New Orleans’ rebuilt levee system has proven it can handle storm surge flooding of at least 17 feet, the peak level of storm surge flooding observed during Hurricane Isaac in August 2012. However, many areas outside this levee system are not as well fortified and suffered destructive storm surge flooding during Isaac. Sally is likely to produce a prolonged and dangerous storm surge from Monday into Wednesday across far southeast Louisiana, Mississippi, Alabama, and far western Florida.
Trabus Technologies maintains a live storm surge tracker for Sally. As of 3 p.m. EDT Monday, the peak surges measured at NOAA tide gauges from Sally were:
3.2 feet at Shell Beach, Louisiana (southeast of New Orleans)
2.7 feet at Apalachicola, Florida
2.6 feet at Waveland, Mississippi
2.4 feet at Panama City Beach, Florida
2.3 feet at Cedar Key, Florida
Paulette makes a direct hit on Bermuda
Hurricane Paulette made a direct hit on the island of Bermuda early Monday morning, with its 40-mile-wide eye encompassing almost the entire island at 5 a.m. EDT. At landfall, Paulette was a category 1 hurricane with 85 mph winds. The hurricane’s winds increased to 90 mph while Bermuda was in the eye; at 9 a.m. EDT, when the rear eyewall was pounding the island, NHC upgraded Paulette to a category 2 hurricane with 100 mph winds.
An island-wide outage knocked out power to 20,000 customers on Bermuda at approximately 1 a.m. EDT, but the Government of Bermuda reported via Twitter at 8 a.m. that the island had experienced “no major issues” during passage of the front eyewall of Paulette. With its years of hurricane experience, Bermuda is well-fortified against storms such as Paulette.
Peak winds reported by the Bermuda airport during passage of Paulette were 55 mph, gusting to 89 mph, but the station did not report a 4 a.m. EDT observation, when the most intense part of Paulette’s eyewall was overhead. Between 2 – 3 a.m. EDT, an observing station at the National Museum of Bermuda reported sustained winds of 62 mph, with gusts up to 96 mph. A weather station in Wreck Road, Bermuda, reported a sustained wind of 80 mph and a gust to 107 mph around 10 a.m. EDT.
With conditions for intensification favorable, Paulette is expected to become a high-end category 3 storm with 125 mph winds on Tuesday, becoming the Atlantic’s second major hurricane of 2020. Increased wind shear and cooler waters will begin a weakening trend on Wednesday. (Note that by the time the hyperactive 2005 season got to the “P” storm, Philippe, that season had already produced four major hurricanes.)
Tropical Depression Rene just hanging on
Far to the southeast of Paulette, slow-moving Tropical Depression Rene was on its last legs Monday. Top sustained winds were a mere 30 mph, and strong wind shear was pushing dry air into the tiny system. Rene will likely become a remnant low by Tuesday.
Tropical Storm Teddy forms in the central Atlantic
Tropical Storm Teddy, which formed in the central Atlantic on Monday morning, was headed west at 14 mph at 11 a.m. EDT Monday with top sustained winds of 40 mph. Teddy is expected to turn to the northwest on Wednesday, well before reaching the Lesser Antilles Islands.
Conditions for intensification will be very favorable late this week, and Teddy is predicted to be a major hurricane by Friday. Bermuda and Newfoundland, Canada, may potentially be at risk from Teddy.
Tropical Storm Vicky forms in the Eastern Atlantic
Tropical Storm Vicky formed in the eastern Atlantic at 11 a.m. EDT Monday, about 350 miles west-northwest of the Cabo Verde Islands. Vicky was headed northwest at 6 mph, with top sustained winds of 45 mph. Vicky will have favorable conditions for development through Monday night, with sea surface temperatures near 26.5 Celsius (80°F), moderate to high wind shear of 20 – 25 knots, and a moist atmosphere. However, wind shear is predicted to rise to a prohibitively high 40 – 60 knots Tuesday through Wednesday, destroying Vicky by Thursday. Vicky is not a threat to any land areas.
Another tropical wave coming off coast of Africa has potential to develop
A new tropical wave, emerging from the coast of Africa on Monday, has some modest model support for development late in the week as it moves west at about 10 mph. Two of the 51 members of the 0Z Monday European model ensemble forecast showed this system would develop into a tropical storm that would reach the Lesser Antilles Islands by Tuesday, September 22.
In its 2 p.m. Monday EDT Tropical Weather Outlook, NHC gave this wave two-day and five-day odds of development of 20% and 50%, respectively. The next name on the Atlantic list of storms is Wilfred — the last name on the list.
Keeping an eye on Gulf of Mexico disturbance
NHC on Monday was monitoring an area of interest over the western Gulf of Mexico producing a few disorganized showers and thunderstorms. Some slow development is possible while this system moves southwestward at 5 – 10 mph over the western Gulf of Mexico this week.
Dry air over the western Gulf of Mexico, however, is likely to inhibit its development, as will wind shear. In its 2 p.m. EDT Monday Tropical Weather Outlook, NHC gave this system two-day and five-day odds of development of 10% and 20%, respectively.
The 2020 parade of record-early named storms continues
Teddy’s arrival on September 14 marks the earliest date that any Atlantic season has produced its nineteenth tropical storm, topping the record held by an unnamed storm from October 4, 2005, which was classified after the season was over. Vicky’s arrival on September 14 marks the earliest date that any Atlantic season has produced its twentieth tropical storm, topping the record held by Tammy from October 5, 2005.
With the Atlantic hurricane season just four days past the climatological half-way point, we’ve already had 20 named storms, seven hurricanes, and one intense hurricane. Only two Atlantic hurricane seasons since 1851 have had that many named storms during an entire season. The record was 28 named storms in 2005, followed by 1933, with 20 named storms. According to Colorado State University hurricane scientist Phil Klotzbach, the averages for this point in the season are seven named storms, three hurricanes, and 1.5 intense hurricanes.
Bob Henson contributed to this post.
Posted on September 14, 2020 (2:39pm EDT).