Hurricane Florence and Potential Local Impacts

Alex

the hype surrounding hurricane Florence has recently picked up some steam on social media, so I’d want to take some time here to outline a little of what we know and what we think may happen over the next week or so. 


I’d like to offer the following discussion with a couple of disclaimers:


1) Tropical cyclone intensity is notoriously difficult to forecast even with the best weather models we have. This is a symptom of the fact that tropical cyclones are governed by things that are very small in scale, and therefore not easily resolvable on weather models.


2) A bad intensity forecast will feedback onto the track forecast, thus creating errors in the track forecasts. Therefore, many of the raw model output maps you might see on social media may be misleading, and without good interpretation by the forecaster may paint a picture totally different than what may happen.


So with that being said, here we go. Hurricane Florence is currently sitting over the south central Atlantic Ocean and is currently a category 3 hurricane. This storm intensified MUCH faster than any model (or forecaster) expected, and did so in a region otherwise not particularly conducive to intensification. Amongst other factors, the temperature of the water in the region over which the storm intensified is not particularly warm. So keeping in mind that the intensity forecast has not been great thus far, we need to take track forecasts with a grain of salt. 


That having been said, the larger scale pattern that has brought much of the heat were currently experiencing is associated with what’s known as a “ridge” of high pressure. The wind around a ridge spins clockwise, and if the storm develops to the southeast of the ridge, it MAY be steered in our direction. BUT the storm may still be captured by an area of low pressure (known as a trough), which would bring it back out to sea. 

So what’s the upshot? Model guidance has trended towards the trough missing the hurricane, thus allowing the ridge to steer it further west towards the mid-Atlantic. Current ensemble and operational model guidance has gradually shown this trend, and given that, my level of concern has begun to slightly increase. At the moment, I’d handicap a landfall of this storm in our area at somewhere around 30%, but that may go up or down depending upon the evolution of both the intensity of the hurricane itself, as well as the larger scale flow pattern. 


For official guidance, I’d reference everyone to the National Hurricane center: nhc.noaa.gov. They issue forecasts every six hours or so and are extraordinarily good at what they do.


So what should you do? Not get freaked out. This is all still hypothetical and very much subject to change. In a certain sense, I’d rather see guidance showing us this type of forecast a week out, as it 1) alerts us to the possibility; and 2) gives it all plenty of time to change. 


With all of this in mind, please note that many social media outlets love clicks. They will post all kinds of crazy weather maps and exclamation points in hopes you’ll see it. Official sources like NHC and NWS are the best for things like this, so just keep that in mind as you read things on Facebook. 


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sprout

Thx WxNut for the probabilities. 

Will not go into panic-mode, but it's a good reminder for me to start stocking up on a few gallons water for hurricane season now.


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max_weisenfeld

Just to say that I am following Florence as well.  The uncertainty and variation in the model output is enormous. 

Unfortunately, one of the models just spit out a projection that hits Long Island hard. Social media and the commercial weather sites are going to jump on this run in the next few hours and you will see a lot of hype.  But this is one plot line, and they are not showing the spread of other tracks from this and the other models. 

It is still way too early to get freaked out here!  We are over a week away and getting very inconsistent runs.


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conandrob240

Potential timing would be helpful. No panic here. Been in the eye last year for Irma. But knowing possible hit date would be useful.


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Alex

One positive that I'm seeing in much of the morning guidance so far is even though the storm continues to trend westward (which, btw, would be a historic track for a number of reasons), the wind isn't quite as strong as it should be for a storm of that intensity. Basically, the lower the pressure, the stronger the wind should be. But sometimes, storms don't follow the rules. Again though, intensity forecasts kinda suck, so it's still pretty up in the air (no pun intended). Still lots of moving parts here, but that big ridge over SE Canada is definitely going to create some problems.


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Alex
conandrob240 said:
Potential timing would be helpful. No panic here. Been in the eye last year for Irma. But knowing possible hit date would be useful.

 Thursday - Friday.


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conandrob240

thank you! Have work in CT Weds-Thurs. Ferry back to LI might be out. Lol


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drummerboy

Hurricane Who-now?


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max_weisenfeld

Florence.

There are also two storms behind it that are getting interesting.  A slow season is heating up.

Details tonight or tomorrow, unless Dr Wxnut is ready to weigh in again.  I want one more model cycle before I have to explain again why I cannot give you any certainty where this one is going to go.


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Alex

Given that all of the morning guidance is now available, I'll weigh in again. I think a US landfall is all but imminent, and the possibility of that landfall being of a major hurricane relatively high. The question of course remains where. Model guidance has consistently been shifting the storm south, a trend that is evident on satellite as well. The loss in latitude is due to both a weakened storm (right now, that will change) and the record setting SE Canada ridge. Given this southward drift, the odds that the storm is able to recurve out to sea continues to decrease.

Many of the operational forecast models are making landfall somewhere around the Outer Banks, with the ensemble models show more spread (as expected). This leaves all sorts of possibilities on the table. The ECMWF (European) ensemble (known as the EPS) is showing an especially interesting set of solutions, with a bifurcation in possible tracks. The EPS simulates the storm 50 times using slightly different initial conditions in order to produce an "envelope" of possible outcomes to give us an idea of "all" the possible scenarios (all is in quotes because theres some issues with this, but for our purposes we'll say its good enough). This mornings EPS shows two clusters of solutions: A cluster of tracks that make landfall somewhere between the Outer Bank and Delaware; and a cluster that make landfall much further south, somewhere between Georgia and North Florida. At this time, I'd still lean towards the northward solution, but that's more of a gut feeling than science to be perfectly honest. If this trend south were to continue however, I think an interesting scenario of a Florida landfall and then perhaps a re-emergence into the Gulf is possible. Although unlikely, its not impossible.

As for us, I don't think were totally out of the woods, but I'd handicap a significant landfall in our area as being pretty low right now. That said, many of the models take the hurricane and curve it back towards us as a tropical storm a couple of days after initial landfall, so we can't rule out heavy rain and some gusty winds at some point.  

As for the systems behind it, they're anyone's guess at this point. It's been a quiet year up until this point (at least in the Atlantic), but we knew that wasn't going to last. 


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ctrzaska

Thanks for all that. 


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mrincredible

So, reasonable actions:

1. Check the generator and let it run for a few minutes

2. Buy a case or two of water

3. Buy some extra batteries ... no more than a 6 month supply

4. Get the propane tanks filled



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conandrob240

still Thurs-Fri?


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Ridley
conandrob240 said:
still Thurs-Fri?

 According to Dr Wxnut’s link, looks like Wednesday afternoon/evening for landfall


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Alex

yes probably a Wednesday landfall down south. Our area impacted a couple days later. 


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Alex

(potentially impacted)


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Alex

NHC's technical discussion tonight is a little ominous. Anyone with family anywhere between Jacksonville and Norfolk should be reaching out and making sure they're prepared. Still plenty of uncertainty on the track, but this looks like the real deal. 

https://www.nhc.noaa.gov/text/refresh/MIATCDAT1+shtml/080251.shtml?

The initial motion estimate is 265 degrees at 6 kt.  Florence is
expected to continue moving slowly westward for the next 48 hours
under the influence of a weak mid-level ridge over the western
Atlantic.  By days 4 and 5, an exceptionally strong blocking ridge
is forecast to develop between Bermuda and the Northeast U.S. and
build westward, keeping Florence on a west-northwestward trajectory
with a notable increase in forward speed by the end of the forecast
period.  It feels like a broken record to mention that the overall
guidance envelope keeps shifting southwestward, and the official
forecast is moved in that direction.  Unfortunately with such a
large well-defined steering current from the ridge becoming likely,
the extended-range risk to the United States keeps rising, which is
confirmed by the majority of the latest ensemble guidance.

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bluepool

Some of the models show a scenario where the storm makes landfall around North Carolina and then moves up the coast toward us... seems less likely but makes me nervous anyway.


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max_weisenfeld

Time to talk about Florence.

This is going to be a long post, but the bottom line is this: although it is too soon to be certain, in the last days large scale weather patterns have caused the forecast track of the hurricane to shift west, and the likelihood that Florence will make landfall on the US coast is rising sharply.

At this time, the most likely landfall would be between Jacksonville, Florida, and Norfolk, Virginia. The track of the hurricane and the trends in the forecast make it unlikely to make landfall directly on New Jersey.

This is very likely to be a major hurricane, with high winds, high tides, and a great deal of rain. People in the southern coastal areas of the USA should be keeping an eye on this storm and beginning to make preparations.

Expected landfall between Wednesday evening and Thursday night. NHC 5-day cone of uncertainty is the first picture below.

Relevant to New Jersey, after landfall, if the storm follows the current plots, the storm, no longer by then a hurricane, may swing up the Appalachians and back east across the northeast bring rain and some wind, although nothing to compare with what those who get it off the ocean would experience.

Now some detail.

Florence has degraded this morning and is for the moment a tropical storm. The conditions that caused this are passing, though, and the storm will re-form into a hurricane shortly. The second picture below shows the GFS model tomorrow night. You can see Florence in red. To the north, over Canada and Greenland, in blue, is a high pressure ridge. This ridge is what is keeping Florence from the original track, which would have been north and out to sea.

The third picture shows Tuesday night into Wednesday morning. The Canadian high has moved east, allowing Florence to turn more to the northwest, heading for the Carolinas. You can also see Hurricane Helene over just east of Africa. For the moment, Helene looks to stay out to sea. Let's wish her well on her journey, far away from us.

The last two pictures are just to give you two images of the level of uncertainty with Florence's track right now. the first shows the GFS model (the US National Weather Service's Global Forecast Model) for Wednesday night, which is really the limit of any sort of real accuracy. You can see there is quite a bit of spread even there in the forecast track possibilities (each of those lines is a possible forecast tract from that one run of the model). That last image is the Euro (the European forecast model system) showing all the possible tracks in it's forecast.


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max_weisenfeld

They are going to be naming invest #9 "Isaac" in a few hours.  That will be three active storms in the Atlantic.


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max_weisenfeld

Florence update.

Much of the data fed into the models when storms are offshore comes from satellites. But, even when the storm is still 1,000+ miles offshore, there are amazing people who will fly airplanes into the storm itself to take measurements. Yesterday afternoon, the planes were able to probe Florence for the first time. As a result, we have more accurate model runs this morning, and the news for the southeast coast is not great.

Satellite images reveal Florence is strengthening again as expected, and the eye is redeveloping (image #1 below). When the NOAA Hurricane Hunters flew through the eye this morning, it was again at hurricane wind speeds. The storm will most like now intensify rapidly. It is expected that Florence will reach cat 4 as it approaches the US coast later this week.

The next few days still look as they did yesterday, with the high pressure ridge steering the storm west until Wed when it will begin a slow turn north. With the addition of the flight data, the models are coming into better consensus on track for the next five days, with an increasing likelihood of landfall Friday between Jacksonville and Norfolk, with the bullseye right now between Myrtle Beach SC and Bald Head Island NC.

After that, there is more uncertainty, especially in the influence of a high projected to occur in the Ohio Valley. This high may slow or stop Florence's forward progress for a time, creating the possibility of many hours of very heavy rain for wherever the storm stalls.

The first image is a current (as of 11:00 this morning) view of Florence. You can see the eye re-forming. On the NHC cone (second image) you can note how the landfall and timing are very similar to 24 hours ago. The last two images are this morning's GFS and Euro, showing how similar the central (mean) tracks are, and how tight the spread of various solutions are for the first 3 - 4 days, which illustrates the models' growing consensus for that time period.

Oh, and for what it is worth, today's (and tomorrow's) weather is courtesy of the remnants of formally hurricane Gordon.

I will be offline until tomorrow night. A sweet new year to those celebrating.


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Alex

This storm has a very real shot at becoming the first category 5 hurricane to make landfall in the United States since 1992. The large-scale pattern and overall atmospheric and oceanic conditions ahead of this storm are very, very conducive to rapid intensification and maintenance of an intense hurricane. The only thing that I think could preclude a category 4+ hurricane at landfall would be a timely "eyewall replacement cycle", in which the inner-core of the hurricane effectively reorganizes itself on the fly. Unfortunately we don't have a great understanding of this phenomenon and have virtually no way to predict it.

If you have any family or friends in the coastal Carolinas, please make sure they evacuate. In addition to the destructive wind and storm surge, it is likely to stall over the area for a day or two, bringing with it the risk of an extended period of heavy rain. One model has 8 feet of rain falling adjacent to the NC/SC coast. 


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drummerboy

well, that's not good news. And hopefully the (rather rare) 2 storms behind it won't amount to much.



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Alex
drummerboy said:
well, that's not good news. And hopefully the (rather rare) 2 storms behind it won't amount to much.



Nothing particularly rare about the storms behind this. But one will stay out to sea and the other is expected to dissipate before it makes any kind of US impact. The latter is still up in the air though.


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drummerboy

Yes, I meant to say that if they turned into 3 hurricanes, that's kind of rare. So far, it's 2 out of 3. From what I read, they occur about every ten years, except the last triple was just last year. So a triple so soon would be kind of an outlier.


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Alex
drummerboy said:
Yes, I meant to say that if they turned into 3 hurricanes, that's kind of rare. So far, it's 2 out of 3. From what I read, they occur about every ten years, except the last triple was just last year. So a triple so soon would be kind of an outlier.

 Yeah, no. It's not kind of rare. Its peak hurricane season. This is what happens.


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nakaille

Just take appropriate precautions, everyone!  Know where your flashlights and batteries are, stock up only on real essentials (water, wine, whatever!) and be prepared to help your neighbors, friends and family.


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DottyParker

Thanks for the crucial info regarding Florence.  I came upon this article from Newsweek which makes some observations already noted by our crack team here. 


www.newsweek.com:  The Bad Thing Florence Could Do: Think Hurricane Katrina 2005.

https://www.newsweek.com/bad-thing-florence-could-do-think-hurricane-katrina-2005-1112835


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conandrob240
nakaille said:
Just take appropriate precautions, everyone!  Know where your flashlights and batteries are, stock up only on real essentials (water, wine, whatever!) and be prepared to help your neighbors, friends and family.

 ? Wait, why? This isn’t supposed to affect our area in any significant way. Do you mean if they are in NC/SC?


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