The arrival of extra-favorable conditions for cyclones could not come at a worse time, coinciding with the traditional peak of hurricane season. In early September, it doesn’t take much to spin up a storm. But when you add to it an atmosphere extremely predisposed to cranking out storms, plus unusually warm ocean waters, look out.
On Thursday, the National Oceanic and Atmospheric Administration issued an updated hurricane outlook that calls for an “extremely active” season, with the likelihood of expending every name on the National Hurricane Center’s current list for 2020. That would require dipping into the Greek alphabet. The up to 25 named storms that NOAA is forecasting is the most it has ever predicted in a seasonal forecast.
In addition to seasonal forecasts through all of hurricane season, it’s possible to make sub-seasonal forecasts, looking two to four weeks into the future. At that range, one can discern broader features that could be supportive for developing tropical cyclones.
Weather patterns conspire in two weeks’ time
Using that approach, it appears the next week to 10 days, through roughly Aug. 15 or 16, will trend toward a lull in hurricane activity. In the near term, there are no immediate signs of any potential storm development, and tropical cyclones are not likely for the time being.
That’s thanks to something called a convectively-coupled Kelvin wave. It’s named after a 19th-century British mathematician and physicist. In brief, this is a large, overturning circulation in the atmosphere, with the wave characterized by sinking air ahead of it and rising air behind. When the air subsides, it inhibits the organized thunderstorm activity needed to cook up a storm.
Conversely, the rising branch of that convectively-coupled Kelvin wave is currently over the eastern Pacific. And that’s where the National Hurricane Center is tracking a tropical disturbance, currently south of Guatemala, that will probably become the next tropical storm in the eastern tropical Pacific Ocean.
Eventually, that rising branch of the Kelvin wave will move east, over the Atlantic. Its presence there will serve to boost the odds of tropical storms and hurricanes.
Around the same time the Kelvin wave’s rising branch arrives, the Madden-Julian Oscillation will swing into a favorable structure for Atlantic storminess, too. The Madden-Julian Oscillation, or the MJO, is a larger overturning circulation than Kelvin waves, which circles the globe at the tropics every 30 to 60 days. It, too, can enhance or dampen the odds of tropical cyclones.
Computer model guidance suggests that the MJO will enter a phase that is supportive of more widespread thunderstorm activity over the tropical Atlantic between Aug. 15 and Aug. 24, although some models delay that a bit.
Why stronger storms could have a better chance of reaching the U.S.
There will be some overlap, known to meteorologists as “constructive interference,” between the Kelvin wave and the MJO. This means the two features could team up to increase the odds of storms more than either of them would on its own.
That alone is problematic, but there are also signals that could favor tropical cyclones making it farther west, with a lesser likelihood of recurving harmlessly out to sea before approaching land. Long-range models suggest the Bermuda high, which is an area of high pressure in the vicinity of Bermuda that often forms at this time of year, will build a bit farther south and west than is typical.
That would influence the atmospheric steering currents that help determine where a cyclone may travel. In an updated hurricane outlook released this week from Colorado State University, meteorologists found well above average odds of a major hurricane (Category 3, 4, 5) making landfall in the Lower 48 states compared with the seasonal average odds.
What to expect
Simply stated, expect an end to August that ranges between busy and very busy, a period that will probably lead into September. By mid September, we’ll be in the climatological peak of hurricane season anyway, so there is no reason to expect a significant slowdown.
The waters off the East Coast are anomalously warm, by as much as 1.3 degrees in the Caribbean and nearly 1 degree in the Gulf of Mexico. Sea surface temperatures are also above average in the Caribbean Sea and the “main development region,” between West Africa and the Lesser Antilles. This is the region that many of the most damaging hurricanes in history have formed.
Warmer ocean temperatures support wetter and more intense storms, while also making rapid intensification more likely. The warmer-than-average waters are in part a product of human-caused climate change.
When a storm rapidly intensifies, the maximum sustained winds near its eye increase 35 mph or more in 24 hours. Rapid intensification was common among Harvey, Irma, Maria, Florence, Michael and a number of the other storms that have affected the United States in the past several years. Rapid intensification is difficult to predict.
Prepare now, rather than when a storm is approaching
If you live near the Atlantic coastline, you are susceptible to tropical storms and hurricanes. Even inland, you may be vulnerable to the remnants of tropical cyclones. Taking steps to prepare now will help you later.
Before a storm brews, learn and understand the nature of the threats that could affect you. If you’re near the shore, wind and storm surge flooding could be your greatest threats. If you live inland, it could be freshwater flooding. In between may mean a mix of it all.
Knowing what threats you are vulnerable to and if you reside in a flood plain, along with heeding the advice of local officials, will help facilitate your decision on whether to stay or leave when the moment arises.
Before a storm, ensure you have a two-week supply of nonperishable food and at least seven days’ worth of medications for you, your loved ones and pets. For water, plan on one gallon per person per day, according to the Federal Emergency Management Agency.
Your “hurricane kit” should contain anything essential you might need. FEMA says this should include a manual can opener, tools, batteries, a flashlight, maps and a whistle to signal for help. The kit should be stored in waterproof, airtight bags.
Because of the coronavirus pandemic, the Centers for Disease Control and Prevention has also joined the conversation on hurricane preparation this year, recommending that personal protective equipment, including sanitizers and masks, be included as well. They also are reminding residents to have toiletries, spare eyeglasses, contact lens solution and other essentials on hand. You should have at least seven days’ worth of medication in your kit, too, according to FEMA.
It is also a good idea to make sure all vital paperwork is digitized, and make copies to keep in your vehicle.
The next two months have the propensity to be extremely busy.
The United States may get lucky, but don’t bet on it. The atmosphere and ocean don’t look to be in our favor.