Hurricane Joaquin forecast: An unknowable storm approaches the East Coast.

How to Make Sense of Category 4 Hurricane Joaquin’s Unknowable Path 

How to Make Sense of Category 4 Hurricane Joaquin’s Unknowable Path 

The Slatest
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Oct. 1 2015 10:17 AM

How to Make Sense of Category 4 Hurricane Joaquin’s Unknowable Path 

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Hurricane Joaquin could hit the United States this weekend. Or not. Either way, there will be significant impacts on land.

Photo by NOAA via Getty Images

Update, 2:30 p.m.: The National Hurricane Center has upgraded Hurricane Joaquin to Category 4 after a hurricane hunter mission investigating the storm found sustained winds of approximately 130 mph and deepening central pressure, both signs of strengthening. 

Looking toward the future, midday weather models continued the trend toward an offshore track for Joaquin. The high-resolution HWRF model joined the larger-scale GFS and European models indicating a future path toward Atlantic Canada or Bermuda. The GFDL and Canadian models, both in the second tier of accuracy, are the only major models remaining to insist on a landfall in the United States, likely in the Carolinas or southern Virginia.

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However, this is not to say that the risk to the United States from Joaquin is decreasing. Latest runs of the GFS and European models—which have high levels of historical accuracy—still indicate 10 to 20 inches of rainfall is likely in the Carolinas over the weekend, regardless of Joaquin's track. That would be enough to break all-time monthly rainfall records for several cities in as little as three days—and create the potential for historic flooding.

Update, 1 p.m.: North Carolina Gov. Pat McCrory has declared a state of emergency for North Carolina. That makes three states—North Carolina, New Jersey, and Virginia—that are bending the rules to prepare for Hurricane Joaquin.

Update, 12:15 p.m.: New Jersey Gov. Chris Christie has declared a state of emergency for New Jersey in advance of Hurricane Joaquin. Christie, who is currently running for president, has pledged to remain in New Jersey until the storm passes.

Original post follows:

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Right now, a major hurricane is threatening landfall in the United States within the next three days. Even worse: Meteorologists—myself included—don’t really know where it’s headed. Since it’s been nearly 10 years since the last storm of Hurricane Joaquin’s strength hit the U.S., it’s understandable that this situation would make more than a few people nervous.

Here’s what we know at the moment:

Overnight, Hurricane Joaquin—which is currently posing a grave threat to parts of the Bahamas—continued its trend of rapid intensification that saw it grow from tropical storm to high-end Category 3 in less than a day. The latest official forecast from the National Hurricane Center predicts Joaquin will reach Category 4 strength later Thursday, if it hasn’t already. On Twitter, NHC director Rick Knabb emphasized the continued threat to the U.S. mainland, saying hurricane watches may be required later Thursday—which would set in motion local preparedness efforts and possible evacuations.

However, overnight weather forecast models have thrown a giant wrench into anything resembling confidence in a likely path for Joaquin over the next few days after it departs the Bahamas.

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For most of the day Wednesday, I talked about the worst-case scenario we might be able to reasonably expect from Joaquin—and that scenario is pretty terrifying: A Category 3 or 4 hurricane landfall in southern Virginia would be catastrophic to a very vulnerable region and could temporarily turn parts of Washington, D.C., into a swamp. It would be like Hurricane Sandy, only for the Chesapeake Bay area.

Thankfully, that scenario is looking a bit less likely Thursday morning. That’s mainly because, over the past 12 hours, the GFS model—America’s flagship weather forecasting tool—for this storm has undergone a dramatic shift from the North Carolina/southern Virginia region that it’s been targeting for the previous day and a half all the way to Nova Scotia, a shift of more than 1,000 miles.

That’s prompted the latest official National Hurricane Center forecast to shift back to the north, toward the New York City metro area, though I don’t think it will remain there for long. That’s because a New York City landfall hasn’t been consistently showing up in any model—it’s merely the NHC’s way of splitting the difference between two very different but roughly equally likely possibilities: a landfall in the Carolinas/Virginia or a track safely out to sea.

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The latest model spread for Hurricane Joaquin covers more than 1,000 miles of coastline, plus a significant chance the storm will turn safely out to sea.

UCAR

Hurricane Joaquin is proving to be an excellent example of the challenges of trying to predict the behavior of a nonlinear system days in advance. Sometimes, that’s just a really, really hard thing to do. There’s a reason chaos theory was invented by a meteorologist. And now, we’re seeing that play out in real time, as possible future paths of a Category 3 or 4 hurricane oscillate wildly over the most densely populated part of the country.

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At the risk of becoming overly philosophical, we’re at a moment in our civilization’s history when stupendous recent technological advances can often make us feel as if we are omniscient. In our pockets, we carry devices that can tell us virtually anything we want, instantly. As much as we may want it to, the atmosphere doesn’t work that way.

To accurately understand what the weather will do days in advance, you have to observe it perfectly—and perfectly understand the underlying physics. We actually do the second part better than the first—there is just no way to launch enough weather balloons or satellites to monitor the entire Earth system, down to the millimeter. On days like today when the weather pattern is especially complex, this uncertainty really sucks, but we sort of just have to sit back and wait to see what the atmosphere will do.

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Hurricane Joaquin near the Bahamas on Thursday morning.

NOAA

In such a situation, it’s best to focus on what we do know:

  • Minor coastal flooding is already occurring along the East Coast from strong onshore winds being funneled between Joaquin to the south and strong Canadian high pressure to the north. That flooding will likely worsen over the next few days, regardless of the track of Joaquin.
  • As Joaquin funnels tropical moisture northward, rainfall totals will be enormous across much of the East Coast regardless of whether the hurricane hits land—we’re talking one to two feet of rain for the hardest hit areas. That will produce flash flooding severe enough to float away cars even in areas far from the coast. It isn’t nearly as dramatic as a landfalling major hurricane, but for many areas, it could be just as damaging. Flooding from heavy rain is more than twice as deadly, on average, as the wind from a hurricane.

Given the potential impact—even if the center of Joaquin moves safely out to sea this weekend—it’s really important to start thinking about steps you might take to be sure you and your family remain safe.

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The latest estimated rainfall projections over the next week. That's a lot of rain over a lot of cities, even if Hurricane Joaquin doesn't make landfall in the U.S.

NOAA WPC

Eric Holthaus is a meteorologist who writes about weather and climate for Slate’s Future Tense. Follow him on Twitter.