Historically, hurricane season peaks about Sept. 10, activity typically in top gear leading into October. But this year’s hyperactive September came screeching to a halt Friday, when Teddy and Beta in the Atlantic and Lowell in the Pacific fizzled or lost tropical characteristics entirely. Since then, the world’s oceans have been virtually silent. But they won’t be for long.
A large zone of rising air at mid-to-upper levels of the atmosphere will soon overspread the Atlantic from the west, at the same time as global circulations favor an uptick in shower and thunderstorm activity. The two factors could overlap to bring about a renewal in tropical busyness.
An area to watch
The National Hurricane Center is already monitoring one area in the northwest Caribbean that could prove problematic in the coming week. The center estimates a 50-percent chance that tropical development will occur sometime in the next five days.
A strip of clumped thunderstorm activity can be seen on satellite north of Venezuela, west of the Lesser Antilles, associated with a weak westward-moving wave at the mid-levels of the atmosphere. The system is rather diffuse, but models hint that a more concentrated lobe of vorticity, or spin, could consolidate along its southern flank.
Uncertainty is a bit greater than normal when it comes to this system, which will probably arrive north of Honduras in the extreme northwest Caribbean by Friday. After that, the details become hazy.
If that blob of spin ends up forming along the central or northern part of that axis of disturbed weather, then the system could latch onto steering currents that would eventually bring it west of Cuba and perhaps into the Gulf of Mexico. But if it becomes established farther south, the system could end up being steered into the Yucatán Peninsula and becoming disheveled before having a chance to organize.
Right now, there is no way to determine which is more likely or whether an in-between scenario may be realized.
But a glance at the long-range pattern — which will feature a dip in the jet stream containing cool air over the eastern half of the country — suggests anything that hypothetically made it into the Gulf of Mexico would be carried north or northeast.
A Central American Gyre
Looking ahead, the upcoming pattern may also prove conducive to the formation of a Central American Gyre, or CAG. Think of it as a sort of broad, weak, whirlpool-like eddy in the mid-levels of the atmosphere that spans 500 miles or more across.
Within this diffuse area of spin, smaller pockets or denser spin may serve to nucleate attempts at developing tropical systems. But it’s impossible to tell where this may occur or whether it does at all.
Some CAG events are effective at pinching off multiple areas of spin, while others struggle. Once in a while, a CAG itself can evolve into a tropical storm or hurricane.
Regardless, heavy rain is a likelihood for portions of Central America in the coming weeks.
Down the road
In the next two to three weeks, there is a chance that tropical activity could become considerably more robust as multiple larger-scale-forcing mechanisms in the atmosphere overlap, including an increase in rising motion over the west Atlantic and an augmentation of thunderstorm activity.
Weather models suggest that, within this extended stretch of favorable conditions, multiple systems may try to take advantage before the end of the month. It’s likely the active stretch will last at least two weeks and, perhaps, carry us into the start of November.
October has a reputation as being a sneaky month for “homegrown” tropical cyclones that develop near the East Coast and Gulf of Mexico, and this year may prove no exception. It’s only September, and hurricane season still has eight weeks to go.