Social media is buzzing this afternoon over the possibility that Tropical Storm Erika could strengthen into a hurricane and threaten the U.S. East Coast next week. However, the forecast is far from certain, and the storm could either make landfall or fall apart or swerve out to sea. Predicting the future is hard, and Tropical Storm Erika represents one of those frustrating limits of weather forecasting.
This forecast is a low-confidence, everything-is-possible extravaganza that relies completely on how well the storm is able to strengthen and maintain its organization in the next few days, so we have to wait and see what it does to get a better idea of what it will do from that point on. Frustrating!, I know, especially if you live near the coast.
Here’s what we know right now.
(If you’re on mobile, the animated satellite loop above is 3.93 MB.)
After days of menacing and teetering on the edge of formation, the National Hurricane Center pulled the trigger at 11 o’clock last night and declared a swirling mass of clouds far east of the Caribbean a tropical storm. This afternoon, it’s...not looking all that good!
Nonetheless, the latest advisory from the NHC shows the storm hauling west at 20 MPH (that’s pretty fast) with a small area of marginal tropical storm force winds—up to 40 MPH—in the patch of thunderstorms near the center. Despite its current appearance, the NHC (and several models) expect the storm to slowly get its act together over the next few days, gradually increasing in strength as it draws closer to the Leeward Islands, the northern part of which are under a tropical storm watch right now.
The above animation shows an exposed low-level center of circulation, with all of the convection to the south of Erika’s swirl. Healthy storms do not look like that. Storms need convection completely surrounding their circulation in order to maintain organization and grow in strength. If the dry air wins and those storms fall apart, Erika’s done. It is an ex-storm. Bereft of life, it rests in peace.
Erika is moving into a layer of dry, dusty air that blew off the Sahara a few days ago, which is even worse news for a storm that’s hanging on by a thread. Given its current state, I’m not too confident that we’re still going to have a Tropical Storm Erika by this time tomorrow—let alone by this weekend—but I defer to the experts on that call. It could very well start getting its act together and become something that makes us nervous.
Strength Is Everything
This graphic is called a spaghetti model, or a compilation of dozens of runs of different weather models that predict where Erika’s center of circulation will go over the next five days. The resulting mess of tracks looks like spaghetti, giving us a really good idea at how much agreement (or lack thereof) there is between the different weather models. A wide spread indicates low confidence and diverging solutions, while tightly-packed lines shows general model agreement and higher confidence in its track.
If Erika survives, it looks pretty certain that it’s going to head toward the west-northwest, but after that, its future is uncertain.
The bad news is that Erika’s ultimate track directly relates to its strength. Remember the tropical storm that was supposed to turn into a hurricane and threaten Hawaii this week? That forecast banked on Tropical Storm Kilo turning into a hurricane, which would have then caught the steering currents and curved northeast into the western part of the island chain. Kilo struggled—much like Erika is right now—and it never gathered the deep thunderstorm activity necessary to embed itself in the wind currents it needed to head toward Hawaii.
The depth and strength of a tropical cyclone is key to where it goes. A weaker storm with smaller, less-intense thunderstorms around its core will be steered by low-level winds. A stronger tropical storm or hurricane with thick, deep, intense thunderstorms surrounding its eye will be steered by winds in the middle and upper levels of the atmosphere.
If Erika manages to strengthen and become a formidable storm in the coming days—as many models say it will, despite its current appearance—we’ll see it roughly follow the track delineated by the National Hurricane Center’s latest forecast. A stronger Erika will be steered by a deeper layer of winds in the atmosphere, which would generally drive it toward the Bahamas. A significantly weaker Erika—a solution supported by the GFS and European models—will get caught in the flow closer to the surface, taking it on a more westerly track, possibly over the Greater Antilles, where it would probably encounter the same fate as now-dead Danny.
This forecast will be a nail-biter until we can get a better idea of what it will do. Social media is currently flooded with computer models showing an enormous hurricane threatening the southeastern United States early next week. That’s a distinct possibility, sure!, but it’s also just as possible that Erika will fall apart, turn out to sea, turn west into the Greater Antilles, or cross into the Gulf of Mexico.
Prepare Now, Just in Case
All options are on the table at this point. It’s going to be something we have to watch like a hawk, and this forecast should be a little unsettling for you to see if you live along the U.S. East Coast. It’s late August. We’re entering the climatological peak of hurricane season, so this is the kind of thing we fully expect to happen, even in an El Niño year.
If you live anywhere near the coast—from Texas to Maine—you should already have a plan and supplies in place in the event of a tropical storm or hurricane. If you don’t have a plan, make one and gather supplies. It’s better to be prepared than caught off-guard.
You should have enough non-perishable food, water, batteries, flashlights, cash, prescription medication, first aid supplies, gas in the car, and hand sanitizer/hand wipes to last you at least a week. Having cash on hand is especially important—debit and credit cards are useless if the power and telephone/internet go out. If you live in an evacuation zone, start thinking about where you’ll go if you’re told you need to leave.
Full advisories from the National Hurricane Center come out every six hours— at 5:00 and 11:00 AM/PM Eastern Time—with position/intensity updates every three hours as long as there are watches and warnings in effect.