Joaquin: Many unknowns

“Reports that say that something hasn’t happened are always interesting to me, because as we know, there are known knowns; there are things we know we know. We also know there are known unknowns; that is to say we know there are some things we do not know. But there are also unknown unknowns – the ones we don’t know we don’t know. And if one looks throughout the history of our country and other free countries, it is the latter category that tend to be the difficult ones.” – Donald Rumsfeld

The quote often gets made fun of, but it’s pretty brilliant. Joaquin fits about all these categories.

This is my effort to enlighten friends, family, and anyone else who may respect my viewpoint on my thoughts regarding Joaquin. Much gets lost in a Facebook post or Twitter comment…here’s where I stand as of 4:30 PM CT on Wednesday.

What: A prolonged significant weather event from the Carolinas, perhaps as far north as New England, but of particular concern in North Carolina and Virginia. Wind, river flooding, rainfall flooding, coastal flooding, and beach erosion are all threats.

When: Primetime looks to be Friday to Sunday, with some risks on either side of those goalposts for longer duration.

First things first: This is not Sandy 2.0. There are many meteorological differences, not the least of which is that Sandy had a massive footprint over a huge chunk of ocean, able to generate massive waves that just obliterated the Jersey Shore.

Joaquin will not have a 500 mile tropical storm wind field in all likelihood. This is not me writing off Joaquin. There are similarities to Sandy…no question. But I want folks in Jersey to understand that this is an entirely different animal.

Now that we have that cleared up, let’s talk about the main threat first: Flooding.

Rainfall/Flooding

By far, the aspect of this storm that is probably most concerning to most meteorologists will be the rainfall that will occur…perhaps both because of AND in spite of Joaquin. The clock on the rainfall forecast map from the National Weather Service below starts at 8 PM ET this evening and goes out a week.

093015_WPC Rainfall
7 Day Precipitation Forecast (NWS)

Yes, that’s 7-10″ of rainfall over a broad area. Recent rains have saturated the ground, thus flooding is likely in spots. In fact, some computer models have been hinting at 12-20″ of rainfall in parts of Western North Carolina and Upstate South Carolina. And that particular model is the one taking Joaquin out to sea!

Key point: Joaquin is a point on a map. Joaquin’s impacts (and thus those of the larger weather pattern) cover a massive chunk of real estate, extending from Georgia through Southern New England. Therefore, do ***NOT*** focus on Joaquin, particularly with regard to rainfall risk. It’s going to rain — a lot, regardless of Joaquin’s final outcome.

Coastal Flooding

Let’s talk coastal flooding risk. Here are tidal forecasts for the Chesapeake Bay Bridge & Tunnel, as well as Atlantic City:

Forecast Tidal Surge Chesapeake Bay Bridge & Tunnel (top) and Atlantic City (bottom) (NOAA)
Forecast Tidal Surge Chesapeake Bay Bridge & Tunnel (top) and Atlantic City (bottom) (NOAA)

I want to point out a couple things. Don’t focus too much on specifics here. These charts are complex, but what stands out? Starting tomorrow, tides begin to increase. This is in response to onshore flow between high pressure to your north and low pressure to your south. Notice, we go through 6-7 tide cycles with pretty high tides. This is a problem. What happens is, you have onshore winds that persist, so as each tide cycle passes and gets higher, less water is able to ebb back out, so you end up stacking up water. Particularly in areas with back bays, that water can often get “stuck” there, leading to prolonged nuisance flooding and in some cases moderate to severe tidal flooding.

Key point: Multiple high tide cycles will likely cause considerable coastal flooding issues regardless of the final track of Joaquin. Where Joaquin comes ashore (if it does) will have surge issues to contend with, but even if that does not happen, you need to plan on significant travel disruptions on coastal barrier islands between North Carolina and New Jersey, possibly as far north as Long lsland.

Wind

Here’s where Joaquin’s final track comes into play. If Joaquin goes out to sea, yeah, it’ll be breezy. But it likely won’t be severe wind. If Joaquin makes landfall, we will have strong winds in about a 100-200 mile radius from the center of the landfall point…possibly a bit further out. The winds near the center would likely be hurricane force. To the north, they’d be tropical storm force at times I would think. Additionally, inland wind, coupled with heavy rain would almost certainly lead to downed trees and power lines, and thus power outages. If you live anywhere under threat, it would probably be wise to have a few days of provisions in case long-duration power outages occur.

So What About Joaquin’s Final Track?

I hate this. I really do, but we simply do. not. know. where Joaquin is going right now. In the meteorology community, you’re hearing about the Euro vs. GFS. The Euro is the model that nailed Sandy well in advance, so it has a justifiable blue ribbon reputation. The GFS recently underwent a massive overhaul that aims to improve it. Well, here’s the test. The GFS slams Joaquin into the North Carolina coast at an angle that is extremely rare for that part of the world, and it would likely maximize storm surge potential from about Cape Henlopen, DE to the Outer Banks of NC. The GFS has support from other global models (UKMET, Canadian, as well as the majority of the tropical models that you often see in “spaghetti” maps…which I will not show).

Then you have the Euro. Oh, yes…the Euro. The Euro plays a very complex game of meteorological “thread the needle.” Without going into details you won’t care about, processes take place that force Joaquin to exit stage right out to sea. Again, this result still causes major rainfall in SC, NC, and VA, but the hurricane itself goes away.

Which model is right? I wish I could tell you. This has a lot of meteorologists scratching their heads right now (including myself). The best I can do for you is illustrate probabilities. I have the utmost respect for the National Hurricane Center, as there are great people working there. They have to stick to certain guidelines and in certain storms that doesn’t always work best I think. Thus, I wanted to annotate the 5 PM ET NHC forecast with my own thoughts.

KEEP IN MIND: These are my thoughts only. Consider them an opinion. I am a meteorologist, but I am not a source of official information. Regardless of what I say, please follow your local NWS office’s advice, local media, and direction of emergency managers.

National Hurricane Center forecast, annotated with my personal thoughts.
National Hurricane Center forecast, annotated with my personal thoughts.

7 AM ET Thursday Update: I am revising odds to:
A: 10% (-10)
B: 20% (-10)
C: 5% (0)
D: 65% (+20)

As you can see, I have started from Saturday and laid out 4 crude scenarios and how I feel about them. These probabilities are based on my assessment of the weather pattern and models right now, and they will change over time.

Scenario A: A left hook into Cape Lookout or further south. I give that 20% odds right now. That would be a major strike for North Carolina, Virginia, and southern Delmarva.

Scenario B: A left hook into the Virginia Beach area, the Chesapeake Bay, Delmarva. I assign this about 30% odds. This is what the models seem to be clustering toward. This would be a major hit for many areas from Southern NJ through NC.

Scenario C: This is the Sandy II scenario with a left hook into NJ. I give this about a 5% chance. No models are explicitly showing this. It is an ultra low probability right now, but as laid out above, even if this doesn’t directly hit you, it could be a bad storm.

Scenario D: This is the Euro out to sea special. I assign this 45% odds right now. This may seem high, but I like how the Euro has handled this system so far relative to the GFS, and I have more faith in how it’s placing upper level features that will determine the outcome of Joaquin. Still, if you want to be technical, I have 55% risk of a hit and 45% risk of a miss, so.

Final words: Again, it’s critical that you heed your local emergency management office’s advice. These folks know what they’re doing. They plan for this. If they say you should do something, do it. Again, also, when crunching the mountains of information being thrown at you, consider again that Joaquin is much more than a dot on a map. It’s a lead actor in an intricate stage production, with a LOT of supporting cast members, all of whom will determine the final scene’s outcome. Stay alert, prepare, don’t panic, but use good judgment.