Subtropical Storm Alpha (2020)

Storm Active: September 18

Around September 14, a non-tropical low formed in the northeastern Atlantic, at around 45 ° N latitude. Unusually, it moved slowly south-southeastward over the following couple of days and then took a turn toward the east. This brought it over at least somewhat warmer water, and some more cloud cover developed near the center. By September 18, based on information from satellite imagery and Portugal-based radar, the system had developed a warm-core and a small, but well-organized convective pattern. As with some northeastern Atlantic cyclones from previous years, the tiny warm-core was still contained in a larger extratropical cyclone. A combination of these factors led to the naming of Subtropical Storm Alpha*, with maximum sustained winds estimated at 50 mph.

With Alpha's formation, 2020's parade of storms continued at a ridiculous pace. Alpha was the 22nd named storm, the earliest, and only second, 22nd storm ever recorded, after Wilma of 2005 which formed on October 17 of that year. After completing the hurricane names list for a given year, the Greek alphabet is used to name cyclones. 2020 was only the second year this was ever required, again after 2005. This wasn't the only strange thing about Alpha. Just a few hours after classification, the storm made landfall in central Portugal, with winds of 50 mph and a minimum pressure of 996 mb. Only Vince of 2005 had made landfall in Europe as a tropical or subtropical cyclone before in recent history, though many cyclones reach Europe after becoming extratropical.

After landfall, the low-level circulation was quickly weakened by its encounter with mountainous terrain, though this did not prevent heavy downpours from occurring in Portugal and western Spain. Less than 12 hours after operationally being classified a subtropical storm, Alpha became extratropical. Its remnants dissipated over northern Spain the next day.

*Note: Though operationally classified on September 18, the post-season analysis in 2021 indicated that Alpha in fact had become a subtropical storm the previous day.

The above images shows Subtropical Storm Alpha just before landfall in Portugal.

The precursor to Alpha spent several days in the northeast Atlantic as an extratropical cyclone (triange points above) and only became subtropical briefly (square points).

Tropical Storm Wilfred (2020)

Storm Active: September 18-20

On September 14, a low-latitude tropical wave moved across the coastline of the nation of Guinea into the eastern Atlantic ocean. The system tracked a bit north of west over the next several days at 10-15 mph and displayed some organized thunderstorm activity. By late on September 17, there was a low-pressure center, and satellite estimates indicated that gale-force winds were occurring. The next morning, a closed circulation developed, so the disturbance was upgraded directly to Tropical Storm Wilfred. Wilfred was the 21st named storm of the 2020 season, surpassing the known storm total for 1933, which had previously had the second-most storms on record with 20 (though totals before the satellite era were likely undercounted). Only 2005 had a 21st named storm previously, Vince, which formed on October 9 of that year, so Wilfred handily beat this record. 2005's 21st storm was a "V" not a "W" due to an unnamed tropical storm identified in post-season analysis. By the same token, Wilfred was only the second time the letter "W" was even used, after 2005's Wilma.

Ocean waters were pretty warm under Wilfred, but the ouflow of massive Hurricane Teddy far to the northwest was already causing increasing shear over the cyclone. Convection became rather disorganized overnight and an uncoved low-level swirl appeared on visible satellite imagery on September 19. Nevertheless, Wilfred maintained minimal tropical storm intensity through the day. Soon after, weakening began and it became a tropical depression. Late that night, it dissipated.

The above image shows Wilfred shortly after formation.

Wilfred spent only a few days as a tropical storm before it succumbed to unfavorable conditions.

Tropical Storm Beta (2020)

Storm Active: September 17-22

During the second week of September, a trough of low pressure formed over the eastern Gulf of Mexico. It produced some showers, but otherwise did not show signs of development. Fortunately for the disturbance, it moved extraordinarily slowly, drfiting generally westward for five days until it was off the coast of Texas. Meanwhile, Tropical Depression Nineteen moved into the Gulf and strengthened into Hurricane Sally, which made conditions near the trough unfavorable for cyclonogenesis. As before, though, it wasn't going anywhere. It next dipped south toward the Bay of Campeche, and was vigorous enough to produce heavy rain near the coastline of southern Texas and Mexico as it went. Around the 15th, a surface low-pressure center formed and gradually deepened. It moved little, but thunderstorm activity became concentrated, culminating in the formation of Tropical Depression Twenty-Two during the evening of September 17.

A trough over the United States tugged the depression slowly toward the northeast or north-northeast over the next day toward the central Gulf of Mexico. Convection increased some, but the center was a bit elongated. Nevertheless, measurements indicated the presence of tropical storm force winds on the 18th, so the depression strengthened into Tropical Storm Beta. Oddly, two additional storms had been named in the time between Tropical Depression Twenty-Two formed and when it strengthened to a tropical storm; these two took the names Wilfred and Alpha, leaving Beta for our depression. Beta was the 23rd named storm of 2020, only the second time this occurred after 2005's Alpha, which was named on October 22 of that year (note that 2005 had an unnamed subtropical cyclone identified after the season's conclusion, explaining why Alpha was the 23rd storm).

Beta strengthened some that evening and its minimum pressure dropped a fair bit. It was still being affected by shear from the steering trough, which exposed the center of circulation overnight. The displaced moisture brought steady rain to southern Lousiana for a day or so. On the 19th, the trough lifted out to the northeast and Beta missed its escape route. Instead, it turned westward and slowed to a crawl as a new ridge built in to the north. Wind shear decreased some too, allowing convection to recover the center that afternoon. The storm had a new threat to deal with: a dry continental airmass approaching from the west. It did a decent job combating this and maintained a central dense overcast. On the 20th, Beta reformed a bit farther west and picked up some speed in that general direction, maintaining its intensity as a moderately strong tropical storm.

By September 21, the system neared the central Texas coastline. Steering currents were collapsing again and Beta slowed down, bringing an extended period of frequent rainfall to some parts of southeast Texas. The storm weakened a bit too due to land interaction. It officially made landfall that night and weakened to a tropical depression during the morning of September 22. Dry continental air eliminated nearly all deep convection, but Beta still was a wet storm at the surface: the Houston area received over a foot of rain from the storm. There wasn't much to steer the cyclone, but it started moving east-northeast over land that afternoon, tracing a weak upper-level trough. The cyclone was far enough from the coast that weakening continued, and it degenerated into a remnant low late on September 22. This low brought moderate rainfall across the south, Ohio valley, and ultimately mid-Atlantic as it moved northeastward for the next several days before dissipating.

Beta was a well-organized tropical storm in the satellite image above, taken on September 20.

The storm took a slow, meandering track through the Gulf of Mexico before making landfall in Texas.

Tropical Storm Vicky (2020)

Storm Active: September 14-17

On September 11, a system emerged off of Africa that was partially associated with a tropical wave that became Teddy in a few days time. An area of vorticity split off and tracked more northward. The next day, it moved over the Cape Verde islands, bringing isolated heavy rainfall. Soon after that, a low pressure center appeared and on September 14, the system managed to develop into Tropical Depression Twenty-One northwest of the Cape Verde islands. A linear outflow boundary approaching from the northwest signaled the arrival of less favorable atmospheric conditions, but the depression nonetheless strengthened into Tropical Storm Vicky later that day. Vicky was the earliest twentieth named storm, or "V" storm, after Tropical Storm Tammy of 2005, which formed on October 5 of that year. Tammy was the twentieth storm of 2005 due to an unnamed storm that was identified in post-season analysis. The 2005 season was also the first to use the letter "V", making 2020 the second such occurrence.

Shear came roaring in out of the west and exposed the center of circulation soon after, but Vicky strengthened a bit more to reach peak winds of 50 mph late that evening. The next day, the system turned toward the west-northwest but persisted as a tropical storm. It seemed that other aspects of the upper-air environment (as well as warm ocean temperatures) were enough to offset the shear a little. Nevertheless, weakening eventually commenced on September 16. The outflow of the nearby and powerful Hurricane Teddy hastened Vicky's demise and it became a remnant low on September 17. Moving south of west now, the low continued on a little further until dissipation occurred.

The image above shows Vicky over the eastern Atlantic, with the Cape Verde islands in the bottom right.

Vicky moved into a highly unfavorable environment after forming and hence was a short-lived tropical storm.

Hurricane Teddy (2020)

Storm Active: September 12-22

On September 10, a fairly well-organized tropical wave entered the Atlantic from the east. It had an ample amount of moisture associated with it and moved steadily westward south of the Cape Verde islands. But as with several previous systems in the 2020 season, there was another tropical wave right on its heels, which had an influence on the first's ultimate development and track. That second wave ultimately became Tropical Storm Vicky. By the next day, the system had a low-pressure center associated with it. Convection wrapped halfway around the center in a curved band over the western semicircle; on the 12th, further organization led to the designation of Tropical Depression Twenty.

There was a little bit of northerly shear affecting the depression, which kept the convection confined to the southern semicircle throughout the next day. Further, the large circulation was still partially embedded in a monsoon trough located in the Intertropical Convergence Zone, which slowed intensification in the short term. Eventually, thunderstorm activity became more concentrated and began to wrap around the circulation. The depression was upgraded to Tropical Storm Teddy early on September 14. This was the earliest nineteenth, or "T" storm, surpassing the record set by the unnamed Azores subtropical storm of 2005, which formed on October 4 of that year.

Teddy had a lot going for it: light shear, warming waters, and plenty of humidity. It began to intensify quickly later that day as it continued just north of west, bringing it to a high-end tropical storm. The increase in winds paused on September 15 as the system took some time to build an eyewall and fight off incursions of dry air. Teddy turned northwest and strengthened again overnight to category 2 hurricane strength. It was a large system, with excellent outflow in all directions but the west. The storm passed well to the northeast of the Lesser Antilles on the 16th, sparing them of any impacts save large waves. Starting that evening, more deep convection developed and wrapped around the eye, which itself warmed and cleared out by early on September 17. Teddy became a very powerful hurricane, rocketing up to category 4 strength by the afternoon and reaching its peak intensity of 140 mph winds and a pressure of 945 mb.

The cyclone underwent some structural changes overnight and became a bit less defined, leading to a bit of weakening. Aircraft and satellite measurements indicated the next day that an eyewall replacement cycle (EWRC) began, in which a new outer eyewall formed, contracted, and eventually replaced the old. These EWRC's are typical for strong hurricanes. They usually lower its top winds, but expand its windfield, and indeed Teddy's wind radii had increased by that afternoon, even though it was down to a category 3. The new outer eyewall became more complete over the next day as the cyclone fluctuated in intensity, but Teddy's EWRC was quite slow. By the afternoon of September 19, the inner eyewall had finally collapsed for the most part, leaving the outer one surrounding a much larger, ragged eye.

Teddy had taken a turn back toward the west-northwest that day, but it soon resumed its northwest course. Environmental factors were becoming less conducive for a hurricane: the storm was tracking over the cold wake left by Hurricane Paulette about a week prior, the air was becoming drier, and wind shear was increasing. As a result, Teddy's eye filled in and it weakened to a category 2. The storm rounded the edge of the retreating subtropical ridge that evening, turning north and then east of north. On September 21, this fortunately brought the center well east of Bermuda, which had just had a direct hit from Paulette. Even so, Teddy was large enough to bring tropical storm conditions to the island from 150 miles away.

The storm began a rather complex interaction with an frontal low approaching from the northwest that day. The lows rotated a bit around one another, accelerating Teddy northward and bending its track back to the left. At the same time, warm Gulf stream waters and a baroclinic energy boost deepened the hurricane even as it began to dsiplay extratropical characteristics. The minimum central pressure dropped back to 950 mb at its lowest during the morning of September 22. By that time, Teddy was a few hundred miles south of Nova Scotia, but was slowing down. The cyclone was certainly a hybrid of tropical and extratropical, though it had enough of a warm core to still be considered a hurricane. Maximum winds decreased to category 1 strength, but Teddy was now extremely massive: rain extended as far west as eastern Maine and tropical storm force winds reached over 300 miles in every direction from the center, including over 500 (!) miles in the northeast quadrant. The entire island of Nova Scotia was within the wind field.

Luckily, Teddy soon lost its baroclinic energy source and also moved over much colder waters, bringing about a steady decay of the cyclone, as well as extratropical transition late that night. The low that had been Teddy made landfall in central Nova Scotia with maximum winds of around 65 mph on September 23 and continued into the Gulf of St. Lawrence later that day. The low was absorbed by a larger system on the 24th.

The image above shows Teddy as a major hurricane over the open Atlantic.

This image is Teddy on September 22 shortly before completing extratropical transition. It was a large, hybrid cyclone, ranking among the largest recorded by gale force wind diameter. The U.S. northeast is visible at top left, along with some smoke in the upper atmosphere from the 2020 California wildfires.

Teddy hit Nova Scotia as an extratropical cyclone, but by then it was weakening significantly, so imapacts were limited.

Hurricane Sally (2020)

Storm Active: September 11-17

An upper-level trough located east of the Bahamas began to produce shower and thunderstorm activity around September 9. It tracked slowly westward over the next day and brought heavy rain to the northern Bahamas. On the 10th, it began to organize very quickly: convection increased and allowed the circulation at the upper-levels to work down to the surface. Sea level pressures were falling by September 11 and the spin tightening. That afternoon, Tropical Depression Nineteen was designated between Andros Island and the south Florida coastline.

Overnight, the depression moved over the southern Florida peninsula. Most rain, apart from some outer bands, was occurring south of the center. Convection continued to increase in this area, but the low-level swirl evident on visible imagery lifted more northward on September 12 and paralleled the western Florida coastline. Surface observations near the tip of the Florida peninsula justified an upgrade to Tropical Storm Sally that afternoon. Sally broke the record for earliest 18th named storm, or "S" storm, crushing the mark set by 2005's Stan, which was named on October 2 of that year.

By September 13, Sally had moved further over the Gulf of Mexico, and was strengthening steadily. The center was still moving west-northwest out a bit ahead of the associated thunderstorms, but overall organization was increasing as outflow and banding became more pronounced. Soaking rains lingered over southwestern Florida through that afternoon until Sally moved farther away. Beginning that evening, a central dense overcast (CDO) exploded over the system and expanded in all directions. The morning of September 14 arrived with a much larger Sally in the Gulf of Mexico, though the centers were still not vertically aligned.

However, Sally's structure underwent another large change later that morning: the old low-level center dissipated and a new one formed farther northeast near the center of the CDO. This sparked a burst of intensification that brought the storm from a strong tropical storm to a category 2 hurricane with peak sustained winds of 100 mph. The surge in wind speeds only halted that evening when some dry air entered the circulation from the southwest. Sally was moving very slowly west-northwestward, only about 100 miles from the Gulf coastline, so that prolonged heavy rains affected the Florida panhandle and soon pushed into coastal Alabama and Mississippi.

By that time, steering currents had largely collapsed and Sally's motion was little more than a drift. The next day, the hurricane turned more to the north, though there were many short-term wobbles, and the forward speed was only about 2 mph. Aircraft measurements indicated that Sally's winds had dropped back to category 1 strength, perhaps due to upwelling of cooler waters or upper-level winds. However, the system's satellite presentation remained very organized and the central pressure actually dropped the afternoon of the 15th to new lows. At first, winds did not carch up, but as the center closed in on the coast, Sally put on one last burst of strengthening. The eye cleared out more than it had at any time previously and the storm regained category 2 strength. Sally was at its peak intensity of 105 mph winds and a minimum pressure of 965 mb when it made landfall just west of the Alabama/Florida border a bit before 5:00 am local time on September 16.

The system turned northeast over land, still hardly gaining speed, and rapidly weakened throughout the day. It became a tropical storm that afternoon and a depression that evening. Torrential rain spread through Georgia and the Carolinas even after Sally was downgraded to a remnant low on September 17. Rain totals along the Gulf coast of Florida and Alabama exceeded 15 inches over a wide region, with over 20 inches in several places. The remnants of Sally finally moved into the Atlantic on the 18th and soon merged with another system.

The above infrared satellite imagery shows Sally intensifying a few hours before landfall.

Sally moved very slowly before landfall and caused widespread flooding in the Florida panhandle and the Alabama coast.

Tropical Storm Rene (2020)

Storm Active: September 7-13

A vigorous tropical wave moved over Senegal and then emerged into the Atlantic Ocean on September 6. Upon hitting water, it already had a well-defined circulation. Only a day later, the system was classified Tropical Depression Eighteen just east of the Cape Verde islands. Ocean temperatures were not as warm in the far east Atlantic and the storm wasn't producing especially strong convection, but it developed banding features. This prompted an upgrade to Tropical Storm Rene the afternoon of the 7th as the system moved over the islands, producing heavy rains and gale force winds. Rene broke the record for earliest "R" storm set by Rita of 2005, which was named on September 18.

The system was moving westward at a fairly fast clip, so it had moved out of the islands by the afternoon of the 8th. Despite a moist atmosphere, Rene had almost nothing in the way of a central dense overcast and in fact weakened briefly to a tropical depression late that night. By morning, however, the system had produced a large burst of thunderstorm activity and it soon regained tropical storm strength. Rene moved west-northwestward throughout the next couple of days and remained pretty ragged. It seemed that dry air aloft was offsetting other favorable factors and preventing Rene from maintaining any semblence of organization. The repeated waxing and waning of the system caused some fluctuations in the intensity, but the system was a minimal tropical storm again on September 11.

Meanwhile, Rene's window of light upper-level winds was coming to a close as a trough to the west began to exert its influence in the form of increasing wind shear. On September 12, the system weakened to a tropical depression and turned more to the right. Intermittent popups were all the storm could manage over the next couple of days as it gradually spun down. The ridge north of Rene began to build back in too and slowed the cyclone's forward motion to a standstill. Unfavorable atmospheric conditions caused the storm's center to lose definition and it degenerated into a remnant low on September 13.

Rene produced little to no deep convection during its time as a tropical cyclone.

After bringing rain to the Cape Verde islands, Rene did not affect any further landmasses.

Hurricane Paulette (2020)

Storm Active: September 6-16, 21-22

On September 2, a tropical wave entered the Atlantic basin from Africa, the latest of a long train of disturbances to do so. The system was quite disorganized, and matters were made worse for it by the presence of another wave nearby and a third several hundred miles further west. The two nearby waves merged south of the Cape Verde islands, while the third was moving little. Two low pressure areas near one another often begin to rotate cyclonically (counterclockwise) around one another by the Fujiwhara effect. This had the impact of shunting the combined wave around toward the northwest. The system it was rotating around dissipated by the 5th and atmospheric conditions for development became more favorable.

Nevertheless, our wave had multiple vortices associated with it. These sprialled inward over the next couple of days. Late on September 6, thunderstorm activity increased too and Tropical Depression Seventeen was designated. The center was still elongated southwest to northeast, but the broader circulation and banding were quite impressive. During the morning of the 7th, the depression became Tropical Storm Paulette. The new earliest "P" storm, it replaced Philippe of 2005, which formed on September 17 of that year. At the time, steering currents around Paulette were quite weak, and it did little more than drift northwestward that day.

The storm strengthened steadily throughout the next day as outflow improved, peaking at 65 mph sustained winds and a pressure of 995 mb. Wind shear from an upper-level trough increased out of the southwest by the later part of day September 8. This displaced convection northeast, eventually exposing the center of circulation and beginning a weakening trend. At the same time, the subtropical ridge built in from the north, which got Paulette moving a bit more quickly toward the west-northwest on September 9. This motion was a bit erratic but the storm generally stayed on the same heading for the next couple of days. Wind shear peaked in excess of 40 kt on September 10, but Paulette continued to generated impressive thunderstorm activity northeast of the center and weakening was only gradual.

Turning toward the northwest on September 11, the system passed through the area of highest shear and moved toward better atmospheric conditions and warmer water. This set Paulette on a strengthening trend once again. The cyclone's structure also changed significantly as the direction of shear shifted from out of the southwest to out of the southeast. Paulette had a bit of a "squashed" appearance, with large, healthy outflow channels to the west-southwest and east-northeast, but a small diameter in the perpendicular direction, once again due to the shear. This was now rapidly diminishing, however. It did not take long for Paulette to take full advantage: a clear eye appeared and the storm became a hurricane late on the 12th.

The storm spent the early part of the day on September 13 mixing some dry air out of the core, and it was successful. The eye became larger and more symmetric during the afternoon and intensification continued. Continuing northwestward, Paulette was aiming straight at Bermuda; conditions there began to deterioriate later that day. At the same time, the storm reached the western extremity of the subtropical ridge and began to recurve, turning toward the north. Paulette hit Bermuda directly before dawn on September 14, with maximum sustained winds of 90 mph and a minimum central pressure of 973 mb. Remarkably, arond 5 am local time, the entire island was inside the eye of Paulette. A little later, hurricane force winds again battered Bermuda as the southern eyewall came through.

The system continued strengthening as it turned northeastward away from the island, reaching category 2 status later that morning. Paulette achieved its peak intensity of 105 mph winds and a central pressure of 965 mb later on the 14th. Meanwhile, it was accelerating northeastward ahead of an approaching cold front. On September 15, ocean temperatures under the storm plunged; combined with the encroaching front, this began to induce extratropical transition and maximum winds decreased. The next morning, Paulette became extratropical. The remnants moved east and slowly weakened before veering south on September 17. Several days later, it passed west of the Azores and then south of them as it turned back toward the east under the influence of a trough over the northeastern Atlantic.

These movements had brought former Paulette over warmer waters again, enough for it to regain deep convection and once again become a tropical storm late on September 21. This classification was short-lived, though. Stable air and cooler water quelled any thunderstorm activity that had redeveloped and Paulette became a remnant low late the next day. The low then reversed course and moved west again. It finally dissipated several days later.

The above image shows Paulette as a category 2 hurricane over the open Atlantic.

Between when Paulette first became a tropical cyclone and its final transition into a remnant low, a remarkable seven named storms formed in the Atlantic: Rene, Sally, Teddy, Vicky, Beta, Wilfred, and Alpha.

Hurricane Nana (2020)

Storm Active: September 1-3

A tropical wave entered the Atlantic on August 23 from the west African coastline and traversed the tropical Atlantic. It began to show signs of development around the 27th, but the process was slow, and the wave was still moving quickly at a low latitude. Early on August 30, the system passed through the Windward Islands. During its trek through the eastern Caribbean, the wave looked much better on satellite imagery, but there was little "under the hood": any low-level vorticity was way south near the South American coastline.

A low pressure center developed a bit later as the system near Jamaica and brought heavy rainfall there beginning late on August 31. After that, a vigorous circulation spun up rapidly and Tropical Storm Nana was named during the afternoon of September 1, already with 50 mph winds! At the time it was located south of Jamaica. Nana broke the earliest "N" storm record, previously held by Nate of 2005, which formed on September 5 of that year.

Aiding Nana were warm ocean temperatures and a moist atmosphere. Hindering it was moderate shear out of the north. This lead to a pattern of oscillating convective bursts: the storm would develop a central dense overcast only to have it retreat toward the south. This limited Nana to a slow rate of strengthening as it continued west, but there was plenty of rainfall on the south side that affected Honduras on September 2. It had enough time to reach category 1 hurricane strength late that evening. It peaked at sustained winds 75 mph winds and a pressure of 994 mb before it made landfall in southern Belize overnight.

Once inland, Nana turned a bit more south of west and rapid weakening ensued. This fortunately limited rainfall totals over Belize and Guatemala. By late afternoon on September 3, the cyclone was a tropical depression. Within a matter of hours, it dissipated over mountainous inland Mexico. The next day, the remnants of Nana emerged into the Gulf of Tehuantepec in the Pacific Ocean, just south of the narrowest isthmus of Mexico. On September 5, these remnants spawned Tropical Storm Julio in the Pacific (the storm received a new name because the low-level circulation of Nana dissipated before reforming). This short-lived storm moved out into the open Pacific before dissipating on the 7th.

The above images shows Nana as a tropical storm on September 2. The cyclone was small and compact and the low-level cloud arcs visible in the northern half of the circulation indicate the effects of wind shear on the system.

Nana dissipated over Mexico, but its remnants moved over the Pacific Ocean.