The tropical Atlantic is expected to continue its highly unusual dormant state this week, which is typically one of the peak weeks for hurricane activity. At 2 p.m. ET Tuesday, the National Hurricane Center was not tracking any named storms and was giving only a 30% chance of seven-day development for two tropical disturbances, one in the central Caribbean and the other off the coast of Africa. The pair were less than enthusiastic about developments in Monday's run of GFS and European modeling duo 0Z and 6Z, with less than half of the members showing development.
The only threat to land is unrest in the central Caribbean, which brought heavy rain to the Dominican Republic and Haiti on Tuesday afternoon. Satellite loops show the disturbance is disorganized, with a small amount of strong thunderstorm activity and not much rotation. Moderate wind shear of 10-20 knots, a fairly humid atmosphere, and near-record warm waters of about 30 degrees Celsius (86°F), conditions were moderately favorable for development—despite large-scale suppression of sinking air developed.
The disturbance is moving west at about 15 mph and will bring heavy rain to Honduras on Friday, with some members of the European Ensemble Model 6Z running Tuesday predicting the potential for a tropical depression to form. The disturbance will bring heavy rain to Belize and Mexico's Yucatan Peninsula over the weekend, and possibly into the southwestern Gulf of Mexico (Bay of Campeche) on Sunday. Some members of the European ensemble model 0Z run on Tuesday predicted that the unrest could move further north early next week and potentially threaten the United States, but the GFS model ensemble was lukewarm on that idea in Tuesday morning's run.
On Tuesday, the National Hurricane Center was tracking two additional disturbances, one in the tropical mid-Atlantic and another off the aforementioned African coast. Both disturbances are expected to move west-northwest, eventually reappear, and are unlikely to pose a threat to the Caribbean Islands or North America.
Why so quiet? An update on forecasters’ headaches, and why probabilistic predictions aren’t “wrong”
The Atlantic is now receiving widespread attention from seasonal forecasters and other hurricane experts who are trying to understand why there has been so little activity since early August. As we discussed in “Where Are the Hurricanes?” There is no shortage of hypotheses in the August 27 article, but it may ultimately take a paper (or several of them) to reveal why this period was so quiet.
One crucial thing to remember is that seasonal hurricane forecasts are probabilistic in nature, even if they are not presented that way. NOAA made clear its possibilities. In its latest outlook update (August 8), NOAA projects a 90% chance of an above-average Atlantic hurricane season and a 10% chance of a less active season than normal. These are the odds of a once-in-a-decade unexpected lull, and in fact we saw just that 11 years ago in 2013. The outlook for the 2013 season is a 70% chance of being above average, a 25% chance of being near average, and a 5% chance of being below average. The year ended up producing a near-average number of 14 named storms in the Atlantic, but only two hurricanes, no major hurricanes, and cumulative cyclone energy of only 36.1, compared with the 1991-2020 average of 123.
As we noted last week, the most obvious factor in recent days has been that the unrest has flowed out of Africa further north than usual – often sucking in large amounts of Saharan dust and dry air – before settling in the main developing region between the Caribbean Limited instability. (Meanwhile, rainfall in the Sahara remains above average, and an article on severe-weather.eu on Monday detailed the once-in-a-century event.)
As boreal autumn approaches, the upper atmosphere will cool faster than the surface in the Atlantic subtropics and tropics, so instability may increase and intensify hurricane activity. Sea surface temperatures remain at record and near-record levels in key formation areas, so there is a good chance of sharp warming in the second half of the season. As many of our readers are well aware, “just one” can cause untold suffering and tens of billions of dollars in damage.
For more information on this strange quiet, see Michael Lowry's recent post on Substack, and the Colorado State University forecaster's two-week outlook for Atlantic activity released late Tuesday, September 3 (link appears at Colorado State University (below the page on the forecast website). The Colorado State University team concluded: “We believe the most likely categories for Atlantic hurricane activity over the next two weeks are below normal (60%), near normal (30%), and above normal (10%) It’s less likely.”
Rainfall in Yagi, Philippines kills at least 14 people; may make large-scale landfall in China
In the Pacific, Tropical Storm Yagi passed through the northern Philippines on Monday local time, bringing heavy rain. Local officials reported at least 14 deaths from flooding and landslides, according to the Associated Press. “Yagi” is expected to become a strong typhoon when it crosses the South China Sea, and may make landfall in southern China around Friday local time, and may make a second landfall in northern Vietnam over the weekend.
The Joint Typhoon Warning Center predicted on Tuesday morning that Yagi would reach a Category 3 peak shortly before making its first landfall, which is consistent with the Category 3 and 4 peaks predicted by the HWRF and HAFS-A models, respectively.
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