The 2020 parade of record-early named storms in the Atlantic continued on Monday, September 7, with the formation of Tropical Storm Paulette in the central Atlantic. Paulette has been joined by Tropical Depression 18 (TD 18) in the eastern Atlantic, which will likely become Tropical Storm Rene later on Monday. Neither storm is on a track that poses a long-range threat to the Caribbean or U.S.

A west-northwest to northwest track into the central Atlantic

Steering currents will carry both Paulette and TD 18 to the west-northwest or northwest during the week. This will put them into the central Atlantic in a location where few tropical cyclones ever go on to make a landfall in the Caribbean or the U.S., making them excellent candidates to be “fish” storms – tropical cyclones primarily of concern to shipping, with no impact on any land areas. There are two exceptions: TD 18 may bring tropical storm conditions to the Cabo Verde islands on Monday evening through Tuesday, and Paulette could affect Bermuda by the middle of next week.

It is likely that as Paulette gets stronger, it will move farther north, where strong winds of an upper-level trough expected to form north of Puerto Rico later this week will have a greater influence on a stronger storm. This trough is also likely to bring higher wind shear, weakening Paulette.

TD 18 is less likely to experience high wind shear from this trough, and more likely to become a hurricane. TD 18 may move slightly faster than Paulette, allowing the two storms to grow close enough late this week to affect each other’s track and intensity.

2020 parade of record-early named storms continues

With three days to go until the typical September 10 frequency peak of the Atlantic hurricane season, we’ve already had 16 named storms, five hurricanes, and one intense hurricane. According to Colorado State University hurricane scientist Phil Klotzbach, the averages for this point in the season are six named storms, three hurricanes, and one intense hurricane.

Paulette’s arrival on September 7 marks the earliest date, in records going back to 1851, that any Atlantic season has produced its sixteenth tropical storm, topping the record held by Philippe from September 17, 2005. Only five more names remain on the 2020 Atlantic list: Rene, Sally, Teddy, Vicky, and Wilfred. TD 18 is likely to become Tropical Storm Rene later on Monday; the record for earliest-forming “R” storm in the Atlantic is September 18, 2005 (Rita).

It is looking increasingly likely that the National Hurricane Center will have to turn to the Greek alphabet, a last resort that’s been used only in 2005. That unforgettable year produced tropical storms Alpha, Beta, Gamma, Delta, Epsilon, and – on December 30 – Zeta.

A potential more concerning storm: the next African tropical wave

Top models for forecasting tropical cyclone genesis are giving strong support for development to a new tropical wave predicted to emerge from the coast of Africa on Thursday.

This wave is predicted to move mostly westward at low latitude at roughly 15 mph next week. Given its lower-latitude position compared to Paulette and TD 18, this new tropical wave may be a threat to the Caribbean and North America. In a 2 p.m. EDT Monday Tropical Weather Outlook, NHC gave the new wave two-day and five-day odds of development of 0% and 50%, respectively.

NHC was also watching an area of low pressure, located just southwest of Bermuda, producing sparse and disorganized heavy thunderstorm activity and moving slowly westward toward the southeastern U.S. In a 2 p.m. EDT Monday Tropical Weather Outlook, NHC gave this disturbance two-day and five-day odds of development of 10% and 30%, respectively.

Typhoon Haishen hits South Korea

Typhoon Haishen roared ashore in eastern South Korea near the city of Ulsan around 7 p.m. EDT Sunday as a category 2 storm with 100 mph winds. Haishen’s eye passed over the eastern side of the city of Busan, South Korea’s second largest city. Remarkably, this was only a few miles from the Busan-area landfall point for category 2 Typhoon Maysak on September 2.

As with Maysak, Haishen could not drive a large storm surge to the coast into the port of Busan (the world’s fifth-largest shipping port), as the winds in Busan blew offshore as the storm approached. However, Haishen caused considerable wind damage in Busan, where sustained winds peaked at 63 mph, gusting to 75 mph, at 7:30 a.m. local time on Monday.

The typhoon knocked out power to over 500,000 people on Japan’s island of Kyushu, where a wind gust of 138 mph was recorded at Nomomachi (Nagasaki Prefecture). Rainfall amounts as high as 600 mm (23.62 inches) were recorded on Kyushu, at Misato on the southeast coast. According to a story from watchers.news, Haishen killed one person in Japan, left four people missing, and injured at least 108 people. South Korea suffered one fatality. South Korea’s Jeju Island received 552 mm (21.7 inches) of rain by 10 a.m. local time on Monday; Yangsan received 296 mm (11.7 inches), and Ulsan received 245 mm (9.6 inches).

An unprecedented battering for Korea

According to NOAA’s historical hurricanes database, between 1945 and 2019 Korea (including both North and South Korea) had not been hit by three typhoons (sustained winds of at least 74 mph) in one year.

So Typhoon Haishen’s landfall was historic, as Typhoon Bavi had made landfall on August 27 in North Korea at category 1 strength, and Typhoon Maysak had made landfall on September 2 in South Korea at category 2 strength. The NOAA database lists 14 typhoons that have passed over South Korea prior to 2020 – 10 at category 1 strength, three category 2s and one category 3. Only three typhoons passed over North Korea prior to 2020, all minimal category 1 storms with 75 mph winds.

Extreme tropical cyclones can breed extreme jet stream behavior

As Typhoon Maysak plowed northwards towards Korea during the first two days of September, it was able to maintain its intensity unusually far to the north because of near record-warm ocean waters created by one of the greatest heat waves in east Asian history.

Ocean temperatures in late August south of Korea were 30 degrees Celsius (86°F) – more than two degrees Celsius (3.6°F) above average. The intense heat wave that helped create these unusually warm ocean waters also brought Japan its hottest day in recorded history – Hamamatsu, Japan, on August 17 tied the record set in 2018 for hottest temperature ever measured in Japan, with 41.1 degrees Celsius (106°F). The extreme heat has carried over into the first week of September, with Sanjo, Japan, setting the nation’s all-time September heat record on September 3, with 40.4 degrees Celsius (105°F).

Supercharged by this remarkable ocean heat, Maysak was able to make landfall in South Korea on September 2 as one of only five category 2 or stronger typhoons on record since 1945 to hit the nation.

When Maysak merged with the jet stream as a powerful extratropical storm on September 2nd and 3rd, the supercharged storm injected a tremendous amount of energy into the jet stream, helping accelerate the winds of that mighty river of air to nearly 200 mph – a wind speed nearly five standard deviations above average. As shown in the tweet (click this link to animate and see the full explanation), the jet stream responded to Typhoon Maysak’s energy by contorting into a series of amplified ridges and troughs downstream from east Asia during Labor Day weekend. That in turn led to formation of an unusually strong trough of low pressure over Alaska, development of a record-intensity ridge of high pressure over the western U.S., and an unusually strong trough of low pressure now taking shape over the Rocky Mountain states.

How climate change is making hurricanes more dangerous

The ridge over the western U.S. brought all-time record heat and intense wildfire activity to many locations in California September 5 – 6. The intense trough of low pressure developing over the Rocky Mountain states is predicted to bring a startling case of weather whiplash to Colorado: places where it was 100 degrees Fahrenheit on Sunday will get snows of 3 – 7 inches on Tuesday. In some locations, these may be the earliest snows on record for the season.

The unusual jet stream behavior behind the current extreme U.S. weather was made more likely by global warming, as part of the ocean warmth that enabled Typhoon Maysak to penetrate so far to the north at high intensity occurred because the planet as a whole is on pace for its warmest or second-warmest year on record – behind only 2016.

As explained in a 2014 paper by Kossin et al., “The poleward migration of the location of tropical cyclone maximum intensity,” typhoons and hurricanes have been growing more intense farther to the north in recent decades, and this effect can be plausibly linked to the changes in global circulation that are causing an expansion of the tropics, which is thought to have a significant link to human-caused global warming.

The unusual jet stream behavior may also be linked to the near-record decline in Arctic sea ice currently underway. As of September 7, coverage of sea ice in the Arctic was the second-lowest on record, behind only 2012, according to the National Snow and Ice Data Center. This is an area of active research, but numerous studies in recent years have linked Arctic sea ice loss to unusual jet stream behavior of the type now occurring (see the excellent June 2020 summary at Carbon Brief).

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Posted on September 7, 2020 (3:41pm EDT)