The bell has rung; Tropics shift into high gear
By Skip Rigney
On August 20th every year, Professor Bill Gray would walk through the offices and hallways of Colorado State University’s Department of Atmospheric Science ringing a bell. The late Dr. Gray, whose expertise was tropical meteorology, wanted to emphasize that the “real” hurricane season was just beginning.
The official hurricane season for the Atlantic basin, which includes the Caribbean Sea and the Gulf of Mexico, begins in June each year. But, there are typically many more hurricanes in the fifty days from late August to mid-October than in the first 80 days of the season, and the middle-season storms tend to be the most intense and dangerous.
So far 2020 has not been typical. Two tropical storms formed in May before the official season even began. Add two in June, five in July, and two during the first 19 days of August, and you have the most named storms to ever develop so early in the season.
How could it get any busier? Well, as if hearing Dr. Gray’s bell ringing on Thursday, two tropical depressions formed, one in the Caribbean Sea and one farther east in the Atlantic. By Monday, both systems are forecast to be in the Gulf of Mexico.
As I write this on Friday morning, the system in the Atlantic has strengthened into Tropical Storm Laura. Laura could become a threat to south Mississippi by Tuesday or Wednesday. If the system in the northwest Caribbean strengthens, it will be named Marco. It is forecast to enter the Gulf on Sunday.
The last time there were two tropical storms or hurricanes in the Gulf simultaneously was June 18, 1959. Tropical Storm Beulah was aimed at Mexico, and an unnamed hurricane was heading toward Tampa, Florida. That’s according to Dr. Phil Klotzbach, a student of Dr. Gray’s, and now a research scientist at Colorado State.
Klotzbach notes that the only other two-cyclone-day in the Gulf, at least that we know about, was September 5, 1933, when a major hurricane made landfall in south Texas at the same time a tropical storm was hitting north Florida.
Whereas the 2020 early season has excelled in terms of total numbers, the storms so far have been generally weak. (Although the hundreds of thousands of people on New York’s Long Island who were without power for days in the wake of Tropical Storm Isaias might disagree.) Only two of the first eleven storms this season reached hurricane status, and those two only made it to Category One status.
Forecasting tropical cyclone intensity is almost always harder than forecasting where the storms will go, and the intensity forecasts for Laura and Marco are even more challenging than usual.
If the storms pull in too much dry air, they will weaken, and dry air is lurking near both systems. If Laura gets too close to the islands of the Greater Antilles, it’s circulation could be torn apart. Marco faces a similar threat from the Yucatan Peninsula of Mexico. Strong winds at differing directions in the upper atmosphere, known as wind shear, are forecast to plague both Laura and Marco from time to time, ripping off the tops of their thunderstorms.
But, it’s late August. The ocean waters are warm.
The bell has rung.