Would-be Tropical Storm Bonnie – a strong disturbance the National Hurricane Center has designated Potential Tropical Cyclone Two – has the appearance of a tropical storm on satellite Wednesday morning but the deceptive clouds cloak what’s happening near the ocean surface, where the system lacks a defined wind circulation to officially classify it as such.
As we discussed in Tuesday’s newsletter, these fine details matter, as without a closed circulation, the Potential Tropical Cyclone can’t begin the process of strengthening and will remain in a state of arrested development.
A big factor stifling the development of Potential Tropical Cyclone Two has been its fast forward motion.
The disturbance has been sailing along at around 25 mph and has accelerated Wednesday morning to over 30 mph.
This is a very fast motion for a wannabe tropical cyclone. In fact, in the deep tropics, more than 95 percent of “fixes” (position and intensity estimates) for tropical depressions, storms and hurricanes are slower than 25 mph.
Of the nearly 70 hurricanes that have formed in the deep tropics during the satellite era (since 1966), only three ever exceeded the 25-mph threshold (Elsa in 2021, Ivan in 2004, and Allen in 1980) and only one hurricane (Elsa last hurricane season) exceeded the 30-mph speed threshold.
Developing systems in particular tend to move more slowly, and even once they form, studies show very fast forward motion exceeding 22 mph pump the brakes on strengthening, which is why we see so few quickly-moving hurricanes.
Potential Tropical Cyclone Two is also grazing the coast of South America, which at least in the short term will limit its development potential.
Once it clears South America Thursday, it’s expected to slow down and, with environmental conditions largely favorable, may take advantage of a narrow window to strengthen before reaching the coast of Nicaragua on Friday.
The system could be upgraded to Tropical Storm Bonnie later Wednesday and is forecast to be near hurricane strength as it approaches Central America later this week.
Also of note, the National Hurricane Center forecasts future-Bonnie to maintain its circulation as a tropical storm through its passage over Central America and into the eastern Pacific Ocean.
If it does so, it would maintain its name (“Bonnie”) in the eastern Pacific and become only the second Atlantic-Pacific crossover storm on record to keep its name in both the Atlantic and Pacific since the rule change took effect back in 2000 (Otto was the first to do so in 2016).
The name “Bonnie” was included in the original six lists of rotating male/female names introduced in 1978 (the tropical cyclone naming lists each year include a male name followed by a female name followed by a male name, etc.; this practice began in the late 1970s when male names were added).
Of the seven Bonnies to have formed in the Atlantic since 1980, although some have been strong and impactful like Hurricane Bonnie in 1998, none has been deadly or destructive enough to retire the name, so it continues to be recycled every six years.
About half of the original 126 names from the six inaugural 1979 lists remain on to this day.
Otherwise across the tropics, an area of low pressure in the Gulf has a very small window for development Wednesday before moving inland over Texas where the upshot will be largely beneficial rains to drought-stricken areas.
Hurricane Hunters are scheduled to investigate the system Wednesday afternoon.
A disturbance in the middle Atlantic will be moving toward the Greater Antilles in the coming days.
While it may bring heavy rains to Puerto Rico and the U.S. Virgin Islands this weekend, it’s headed into the teeth of hostile wind shear, so development beyond the next few days is unlikely.