Visible image from NASA's Terra satellite of Typhoon Maysak on August 31, 2020, after the storm had moved past Japan's Ryukyu Islands (outlined). (Image credit: NASA Worldview)

Fearsome Typhoon Maysak began angling toward the southern coast of South Korea on Tuesday, September 1, after swinging through Japan’s Kyushu Islands as the equivalent of a Category 4 hurricane. Maysak is on track to slam populous southeastern South Korea on Wednesday night local time with sustained winds that could exceed 100 mph, together with a destructive storm surge.

Typhoon Maysak could become one of South Korea’s strongest typhoons on record

Maysak’s eastern eyewall – the most dangerous part of this storm – passed directly over Japan’s tiny Kume Island on Monday night. A peak wind gust of 54 meters per second (about 122 mph) was reported at Kitihara on Kume Island, which received almost nine inches of rain in 24 hours, according to weather.com’s Jonathan Erdman. Hurricane chaser James Reynolds (@EarthUncutTV) documented shrieking winds and huge waves.

“Happy to report I saw no major building damage on Kumejima which is to be expected, these islands are built for the strongest typhoons,” Reynolds tweeted. “Power is out in many places and lots of cleaning up to be done.”

Maysak is continuing to track toward a potential landfall west of Busan – South Korea’s second-largest city and the world’s fifth-largest port. That track would put the Busan area on the storm’s more dangerous eastern side. Maysak then will angle leftward, taking an unusual course near the peninsula’s east coast that could bring torrential rains and high wind across both South Korea and North Korea and into far northeast China as the typhoon transitions into a strong extratropical storm.

Even if Maysak passes far enough west of Busan to spare the city its strongest winds, the storm’s broad, powerful circulation likely will push a substantial storm surge toward the Busan area, where the geography is particularly prone to surge impacts. What’s more, typhoons appear to be delivering stronger surges to the Busan area even after sea-level rise due to climate change is taken into account. A 2016 study in the Journal of Coastal Research led by Sang Myeong Oh found that typhoon landfalls from 1962 to 2014 drove a seven-inch increase in the annual maximum surge height (AMSH) in Busan, a rate of increase about 50% higher than the local trend in mean sea level (MSL).

On the plus side, Maysak has embarked on a weakening trend that will cut its top winds prior to landfall. Vertical wind shear is increasing, and the typhoon’s once-distinct eye became fragmented on satellite imagery on Wednesday. Moreover, the western half of Maysak will be passing over a cool wake left behind by Typhoon Bevi, which passed west of the Korea Peninsula just a week ago. Sea surface temperatures (SSTs) in this wake are lower than the standard 26°C (79°F) threshold for sustaining a tropical cyclone (though much warmer just to the east, where the bulk of Maysak will be traveling). There is also the possibility of an eyewall replacement cycle, the “shedding” of an old eyewall that can reduce a tropical cyclone’s strength for a day or so. In this case, Maysak would have to rebuild a new eyewall quickly under less-than-optimal conditions before making landfall.

Figure 1. Forecast from the 6Z Tuesday, September 1 run of the HWRF forecast model showing Typhoon Maysak nearing landfall on the south central coast of South Korea at 15Z Wednesday (midnight Wednesday night Korea time) with a projected central pressure of 934 mb and top sustained winds of 90 knots (about 105 mph). This is not an official forecast of landfall location and strength. (Image credit: tropicaltidbits.com)

All things considered, it remains possible that Maysak will strike South Korea with a central pressure below the national record of 950 mb, as consistently indicated by multiple runs of the HWRF model (one of the best for tropical cyclone intensity).

Widespread 4-8 inch rains from Maysak will be falling atop ground soaked by South Korea’s second wettest monsoon season on record, and also by rains from Typhoon Bevi just last week.

Next up: Haishen

More trouble lies on the horizon with Tropical Storm Haishen, now gathering strength in the Northwest Pacific. Long-range models show that Haishen could reach Category 4 strength on a course that will take it over or near southwest Japan by Sunday, and perhaps toward the Korean peninsula as a weakening system after that.

Figure 2. Departures from average sea surface temperature (degrees Celsius) across the Northwest Pacific on September 1. (Image credit: tropicaltidbits.com)

Monsoon and typhoon season over the tropical Northwest Pacific had been remarkably calm until the last few days of August. For the first time in the satellite era, no typhoons were reported during July. As one might expect in the warming climate, the lack of activity to churn up the waters allowed the Northwest Pacific to warm to record or near-record levels (see image below). These warm waters will give a major boost to Haishen as it heads toward Japan.

Tropical Storm Nana expected to drench northern Honduras

On Tuesday morning, September 1, NOAA’s National Hurricane Center (NHC) dubbed a strong disturbance south of Jamaica Potential Tropical Cyclone 16. NHC uses the “potential tropical cyclone” (PTC) designation, first used in 2017, for any system that is not yet a tropical cyclone (meaning a center of low pressure with a warm core and a closed circulation at the surface) but one that could affect land as a tropical storm within 48 hours. The system was upgraded to Tropical Storm Nana on Tuesday afternoon.

Figure 3. GeoColor visible satellite image of Potential Tropical Cyclone 16 at 1600Z (noon EDT) September 1, 2020. (Image credit: RAMMB/CIRA/Colorado State University)

Though PTC 16 did not have a closed surface circulation on Tuesday morning, it was a healthy disturbance, with a distinct cluster of showers and thunderstorms (convection) and upper-level spin evident. The system was hustling westward at 18 mph with top sustained winds of 40 mph, moving atop warm SSTs of around 29°C (84°F).  On its upgrade to Nana, the winds were boosted to 50 MPH.

Oceanic heat content is very high along Nana’s path, so if the system does organize, it will have plenty of warm water to access. The atmosphere will be steadily moistening, with mid-level relative humidity climbing above 60%. Moderate to strong wind shear (10-20 knots) will be the main cap on any rapid strengthening of Nana.

NHC predicted Nana will head westward toward a likely landfall in Belize on Thursday. A tropical storm watch was issued for Belize and the north coast of Honduras. Given the mostly favorable conditions ahead of it, Nana could reach hurricane strength before landfall.

As Nana parallels the Honduras coast, its strongest winds are expected to remain offshore on the right-hand (north) side. Heavy rains may extend across the rugged coastal area and adjacent islands.

The next two names on the Atlantic list are Nana and Omar. The earliest fourteenth storm of any Atlantic season in records back to 1851 is Nate (September 5, 2005), so this year is likely to continue setting a record pace.

Figure 4. GeoColor visible satellite image of Tropical Depression 15 at 1620Z (12:20 p.m. EDT) September 1, 2020. (Image credit: RAMMB/CIRA/Colorado State University)

Tropical Depression 15 clinging to life off the Southeast Coast

Tropical Depression 15 continued to spin on Wednesday morning about 140 miles east-southeast of Cape Hatteras, North Carolina. TD 15 was moving away from the southeastern coast at about 14 mph, and no U.S. impacts are expected. Westerly wind shear was keeping the disorganized convection associated with TD 15 well east of the center of circulation. As it moves across very warm waters (SSTs of 30°C or 86°F), the depression could briefly bump up to minimal tropical storm strength before it gives in to the destructive effects of rapidly increasing wind shear.

Far out in the eastern Atlantic, several tropical waves have tried to organize themselves without success over the past few days. NHC is now pegging a wave just coming off Africa with a 40% chance of development between Thursday and Sunday as it heads west across warm tropical waters. If it holds together, this system would not reach the longitude of the Lesser Antilles until next week.

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Posted September 1, 2020 (2:24pm EDT)

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...

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