While we’ve stressed over the eventual track of powerful Hurricane Joaquin over the next few days, a concerning number of people may not be aware that a significant—potentially devastating—flash flood event will take place with or without the hurricane coming close to land. Many spots could see more than a foot of rain this weekend.

Biblical Rainfall

The driving force for all of the big weather we’ll see over the next couple of days is that sharp trough in the jet stream that’s digging across the eastern United States this afternoon. The trough will grow even sharper by tomorrow, with an upper-level low (and eventually a low pressure system at the surface) wringing out a deep slug of tropical moisture in the atmosphere over the southeast.

The result will be rain, and lots of it. We could be staring down an event that will shatter many all-time rainfall records, bringing with it the potential for a significant flooding event over a wide stretch of real estate.

The Weather Prediction Center’s latest forecast shows a huge area of ten or more inches of rain across South Carolina and small parts of Georgia and North Carolina, with a bullseye of 15 or more inches possible in parts of western and central South Carolina, including Greenville. Radiating out from there is a widespread area of five or more inches of rain.

The heaviest rain will begin tonight and could last through Monday night.

Remember that the rainfall totals above do not take into account the potential for Hurricane Joaquin to make landfall. This is rain on its own, caused by a separate event that will influence the track the hurricane takes. If the hurricane does veer west and make landfall, it will turn an already-bad flooding event into an absolute disaster.

It’s important to note that the rainfall predictions from the WPC are generalizations—actual rainfall totals will be much more localized than this, with spots caught under the heaviest showers and thunderstorms potentially seeing much higher totals, while places that manage to escape a constant train of precip seeing rainfall totals that wind up under what’s currently forecast.

Hurricane Joaquin

Joaquin continues to lash the Bahamas as a major hurricane this afternoon as it very slowly moves toward the southwest at 6 MPH. As of 5:00 PM EDT, the storm is now a category four with 130 MPH winds, and it’s expected to maintain this intensity (or strengthen just a little bit) over the next day before it starts to weaken on Saturday.

While we’re heavily focused on what could happen here in the United States, this is an extremely bad situation in the Bahamas. The hurricane is moving just slow enough that several islands have experienced hours upon hours of hurricane force winds, torrential rain, and a significant storm surge. Many structures on the islands are built for hurricanes, though, so hopefully the folks there are safe and will come out of the storm without much of a toll on humans or property.

Normally, this is where I would generate a pretty map showing the National Hurricane Center’s cone of uncertainty along with the forecast points and watches/warnings in effect. I’m not going to do that this time around. Hurricane researcher Brian McNoldy posted a good article at the Capital Weather Gang explaining the major shortcomings of the cone of uncertainty in a situation like this.

The cone of uncertainty shows you the average historical track error in the NHC’s forecasts for previous storms. As you get farther out in time, their average margin of error increases by several dozen miles. By the end of the forecast period—five days—the average track error over the past five years has been something like 250-260 miles. It’s a static cone that doesn’t take into account large model spread like we’re seeing right now.

The current NHC forecast—you know, the one pointing Joaquin toward the Northeast—is a compromise forecast. It’s splitting the difference between models that send Joaquin into the East Coast and models that send Joaquin out to sea. I’m willing to say it’s unlikely—not impossible, but unlikely—that Joaquin will split the difference and head toward Long Island.

Here’s the discussion straight from the NHC explaining why they issued the forecast they did at 11:00 AM:

This pattern evolution should cause Joaquin to turn northwestward in 24 hours or so and then turn northward. After 36 hours, the guidance remains very divergent. The Canadian, GFDL, HWRF, and NAVGEM models forecast Joaquin to turn northwestward and make landfall over the Carolinas and mid-Atlantic States. The ECMWF continues to forecast a slower northeastward motion taking Joaquin near Bermuda and out to sea. The UKMET and GFS are in between these extremes showing a generally northward motion. Given the spread and the possibility that the 1200 UTC guidance could show additional changes, the forecast track after 36 hours is nudged only slightly to the east at this time. The new track lies to the east of the landfalling models, but to the west of the GFS, UKMET, ECMWF, and the various consensus models. Further adjustments to the track may be needed later today depending on how the models do (or do not) change.

Given the fact that it’s a compromise that splits the difference between hard left and hard right, I’m going to skip posting it this time around. The forecast map is over at the National Hurricane Center’s website if you want to take a look at it. Hopefully things will be clearer at the 5:00 PM or 11:00 PM EDT advisories.

Long Live the Euro

They’re popping bottles in England today as the European model seems poised to have landed a decisive win in the battle of the computer algorithms. Hurricane Joaquin is encountering a complicated weather pattern in which one small change could have a dramatic impact on the final outcome. For the past few days, we’ve lurched from one model run to the next in an attempt to nail down Hurricane Joaquin’s ultimate track; most models said it would veer west into the United States, while the European model held steady for days in insisting that the storm would head out to sea.

Thankfully, the GFS (American) model has swung around to the Euro’s point of view, sending Joaquin parallel to the East Coast before hanging a right near Atlantic Canada and heading out into the open ocean. This is not a done deal, however. The above graphic is a spaghetti model showing the different tracks Joaquin’s eye takes according to different models. The resulting tracks look like spaghetti—closer lines indicate greater consensus than lines that are spread out.

Even though the GFS and Euro now show an offshore solution for Joaquin, there are some models that still show Joaquin making landfall on the East Coast. You can’t let your guard down yet—anyone from Charleston to Boston needs to watch this storm like a hawk. If this storm does make landfall, it will turn an already-dangerous flooding situation into a disaster.

Prepare Anyway

The list below is the same as the one I wrote for yesterday’s post about Joaquin, with an added point about pets. It’s important information, not only to prepare for the hurricane, but to also prepare for the potential for extensive inland flooding from the big rainfall event that will precede any potential effects of the hurricane.

  • With already-saturated ground, it won’t take much wind to knock down trees and power lines. If your municipality’s water pumping station loses power and they don’t have a backup in place, you lose your running water.
  • Make sure you have enough non-perishable food and bottled water to last everyone in your household a week or longer. Canned food like ravioli, peanut butter and jelly, bread, durable fruit (for example, fresh, whole apples hold up well), stuff like that.
  • Don’t forget about food and supplies for your pets.
  • Just before the worst of the storm, fill up your bathtubs and sinks with water. You’ll need this water to pour in your toilet tank to flush if water service goes out.
  • If the power goes out, you’ll need plenty of batteries to power flashlights and radios. Candles work for lighting, too, but you need to watch them like a hawk. The only thing worse than a bad storm is your house burning down during a bad storm.
  • Think about your cell phones—portable chargers or car chargers are a must. Make sure you have another way to communicate (and old flip phone or landline) in case something happens to your cell phone. If you have an old cell phone lying around, they can still dial 911 even if it’s not connected to a paid service anymore.
  • Keep your car as full of gas as possible and make sure the battery isn’t on its last gasps. If your power goes out, your car will serve as your giant, expensive phone charger, if nothing else.
  • Keep some cash on hand. If the power, telephone, and/or internet go down, you won’t be able to use debit or credit cards.
  • Make sure you have prescription medicine to last you a week or longer.
    Prepare a first aid kit complete with stuff like bandages, peroxide, antibacterial cream, pain medication, and stuff to calm down an upset stomach.
  • Make sure you have enough personal hygiene products—stuff like toilet paper, deodorant, pads and tampons, toothpaste, and all that. Don’t forget hand sanitizer and baby wipes in case the water goes out. Keeping your hands clean could prevent a nasty illness.
  • Photograph and document valuable belongings in case they’re damaged or lost during the storm. It’ll help for insurance purposes, if not just to look back and remember them one day.Keep important documents (social security cards, birth/death/marriage/divorce/immigration/deed papers, diplomas, business documents you’re hiding from the government, etc.) in a watertight, safe location. Put them in one waterproof container after the other if possible.

Flood Safety

With the amount of rain expected to fall over areas where the ground is already saturated, even areas that don’t normally flood could see significant problems with so much precipitation on the way.

If you live in a flood zone, you more than likely already know what to do. If you go under a flood or flash flood warning, get to higher ground as soon as possible. If it’s too late, get as high in your home as possible and let emergency crews know where you are so they can come rescue you during/after the event.

Make a mental map and think of all the routes you take on a normal day. Check around to see if those roads flood when it rains heavily—make sure you have a couple of routes to get to work/school and back home if one or more of your routes is flooded out. If at all possible, stay home during the heaviest rain.

The number one reason people die in floods in the United States is because they tried to drive across a flooded roadway, underestimating the depth of the water only to drown before help could arrive. It doesn’t take much water to lift a vehicle and carry it downstream—only a foot in most cases. Even large vehicles like pickup trucks can stall out and/or get hurled downstream.

It sounds like common sense—it is!—but do not drive through a flooded roadway. Every year, thousands of people do it, and many of them get stuck and force rescue crews to risk their lives to swim out there and rescue them or recover their bodies. There is nothing on the other side of a flood that’s worth risking your life and the lives of those who have to rescue you.

Full forecasts from the National Hurricane Center are issued at 5:00 and 11:00 AM/PM, with position and wind updates every three hours in between. Local National Weather Service offices are responsible for issuing flash flood watches/warnings, as well as rainfall forecasts for individual locations.

[Satellite Loop: NASA and NOAA | Jet Stream: Tropical Tidbits | Spaghetti Model: WeatherBELL | Rainfall Map: author | I updated this post at 4:52 PM to embed a new map showing updated rainfall predictions from the WPC.]

Email: dennis.mersereau@gawker.com | Twitter: @wxdam

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