Above: Infrared image of Tropical Storm Vongfong at 1720Z (1:20 pm EDT) Tuesday, May 12, 2020. (RAMMB/CSU/CIRA)
The first named storm of 2020 in the entire Northern Hemisphere—Tropical Storm Vongfong—has developed, and it is expected to be an intensifying typhoon as it approaches the central and northern Philippines later this week. Update (3 pm EDT Wednesday): Already a Category 2 typhoon, Vongfong is now expected to strike the Philippines as a Category 4 storm on Friday local time (see below).
Meanwhile, a disturbance expected to take shape just northeast of The Bahamas could take on subtropical characteristics by the weekend. Update (3 pm EDT Tuesday): In a special Tropical Weather Outlook, NOAA/NWS National Hurricane Center gave the system a 70% chance of subtropical development between Thursday and Sunday.
The Bahamas disturbance is expected to be triggered by a pocket of energy in the subtropical jet stream. Now in the Northeast Pacific, this upper-level impulse will race across northern Mexico around Thursday and Friday and approach Florida and The Bahamas this weekend. As it does, the impulse will roll atop a decaying frontal zone left behind by the sprawling, chilly dome of high pressure dominating the eastern U.S. in recent days. As noted by weather.com, Florida’s east coast can expect several days of onshore flow around this high; there’s a high risk of rip currents through Friday along coastal Broward, Miami-Dade, and Palm Beach counties.
Any development would more likely be subtropical rather than tropical, given the existing frontal zone and the fact that sea-surface temperatures are still on the cool side—around 24°C to 26°C (75–79°F). That’s about 0.5°C above average for this time of year but still at or just below the typical 26°C threshold for tropical development.
Whatever forms in the next few days is very unlikely to directly affect Florida. The ECMWF and GFS ensemble runs from 0Z Tuesday agree with prior runs in taking any development northeastward from the vicinity of The Bahamas, away from the U.S. East Coast. Both ensembles had less than a 10% chance of the system affecting the Southeast U.S. coast, including Florida, and similarly low odds that the system would become a subtropical or tropical storm. As suggested by the NHC outlook, there’s a somewhat better chance that this system could become a subtropical depression.
Yet another early-season named storm?
The Atlantic’s hurricane season doesn’t start till June 1, but it’s become increasingly common in recent years to get our first named storm in the pre-season period. Each year since 2015 has had at least one named storm before June 1, and there were a total of eight pre-June named storms in the last decade, as shown below. All of these were tropical storms unless otherwise noted.
2012: Alberto (May) and Beryl (May)
2015: Ana (May); became a subtropical storm, then tropical storm
2016: Alex (January), a hurricane affecting the Azores, and Bonnie (May)
2017: Arlene (April); began as a subtropical depression, then tropical depression and tropical storm
2018: Alberto (May); became a subtropical storm, then tropical storm
2019: Andrea (May), subtropical storm
The Atlantic hurricane season does appear to be getting longer in the region south of 30°N and east of 75°W, according to a 2008 paper by James Kossin (University of Wisconsin–Madison) in Geophysical Research Letters. A 2016 analysis by Ryan Truchelut of WeatherTiger also supported this idea. However, Juliana Karloski and Clark Evans (University of Wisconsin–Milwaukee) found no trend in tropical cyclone formation dates when looking at the entire Atlantic for the period 1979–2014. Note that subtropical cyclones were not recognized by NHC until 1972 and were not officially named until 2002.
Vongfong a heavy rain/flood threat for the Philippines
A tropical depression several hundred miles east of the central Philippines was named Tropical Storm Vongfong early Wednesday local time, with top sustained winds set at 35 knots (40 mph) by the Joint Typhoon Warning Center (JTWC). The name Vongfong means “wasp” in Cantonese, noted Matthew Cuyugan on Twitter.
Vongfong is already fairly well structured, with an expanding zone of showers and thunderstorms (convection) and moderate outflow at upper levels. Vongfong will benefit from low wind shear (less than 10 knots) for the next couple of days, along with sea-surface temperatures of around 29°C (84°F) and a moist mid-level atmosphere (near 70% relative humidity).
Vongfong is predicted by JTWC to arc westward and attain minimal typhoon strength by the time it reaches the central Philippines on Thursday local time. Update: In its 12Z Wednesday forecast update, JTWC pegged Vongfong's top sustained 1-minute winds at 105 mph, and the center predicted that Vongfong's rapid intensification trend would continue. Vongfong may make landfall on Thursday night or early Friday local time near Catanduanes island as a Category 4 typhoon.
After it reaches the Philippines, Vongfong is projected to gradually recurve northward, possibly running along or near the length of large and populous Luzon island. Such a track would dent its strength over time but could lead to a serious heavy rain and flooding threat, with the GFS model suggesting that localized rainfall amounts on the order of 10” – 20” would be possible.
Vongfong is the year’s first named storm in the Northwest Pacific as well as the entire Northern Hemisphere, kicking off what’s been an unusually slow start to tropical cyclones north of the equator. On average (1981-2010), through May 12, there have been two named storms in the Northwest Pacific and a total of more than 11 named storm days globally, based on statistics from Colorado State University’s real-time monitoring of cumulative tropical cyclone activity.
The East Pacific's hurricane season officially begins on Friday, May 15.
Potential Bay of Bengal storm this weekend
WU cofounder and Cat 6 founder Jeff Masters has this update on a potential threat in the Bay of Bengal next week:
“Two of our top models for predicting tropical cyclone genesis--the GFS and European models-- predicted in their most recent runs that the first named storm of the season in the North Indian Ocean would form this weekend, in the Bay of Bengal. Some of the most devastating tropical cyclones in world history have occurred during the May pre-monsoon tropical cyclone season in the Bay of Bengal, and residents of India, Bangladesh, and Myanmar should monitor any potential development this weekend. Ocean temperatures are exceptionally warm over the Bay of Bengal—near 31°C (88°F), which is over 1°C (1.8°F) above average. Both the GFS and European models predicted that a hurricane-strength Tropical Cyclone Amphan would be in the Bay of Bengal early next week.”
Dr. Jeff Masters contributed to this post.