Advice on storm watching …

Well, it’s that time of year again. The annual angst-fest known as hurricane season. This is my semi-annual post on how to find information, interpret the outlooks, think about invest areas, ponder track models. If you know what you’re doing you can skip this one, but if you want my view on how to reason with hurricane season, need a refresher, or just want the usual dose of snark, read on …

Lots of media personalities, bloggers, and random people who stop me in parking lots think they have the inside scoop on hurricanes. Forget apps or pack animals overly fond of adult beverages. The only really reliable public source of hurricane forecasts and data for the Atlantic and East Pacific is the US National Hurricane Center (https://www.nhc.noaa.gov). Your first stop is to examine the tea leaves known as the Tropical Weather Outlook. It’s the first thing you see when you go to the NHC site. While the graphic is of some use, the really valuable information is in the text that accompanies the graphic. It is right below the picture. You can select the region (Atlantic, East Pacific, or Central Pacific – Hawai’i), and the time frame – 48 hours or seven days. As of today, the picture is rather boring:

So let’s look at an example from last year:

Here is the text that goes with the above graphic:

ZCZC MIATWOAT ALL
TTAA00 KNHC DDHHMM

Tropical Weather Outlook
NWS National Hurricane CenteButr Miami FL
200 AM EDT Fri Jun 16 2023

For the North Atlantic…Caribbean Sea and the Gulf of Mexico:

Eastern Tropical Atlantic:
A tropical wave located near the west coast of Africa is producing disorganized showers and thunderstorms. Environmental conditions appear to be conducive for gradual development, and a tropical depression could form during the early to middle portions of next week while the system moves westward at 15 to 20 mph across the eastern and central tropical Atlantic.
Formation chance through 48 hours…low…near 0 percent.
Formation chance through 7 days…medium…40 percent.
Forecaster Cangialosi

These messages follow a set format with a very careful use of language that makes it really easy to decide if you need to panic or not. Each potential system is described and, if it is real threat, the following phrase will appear: Interests <somewhere> should <do something> . If this phrase doesn’t appear, then the storm is nothing to worry about in the short run (next day or so), and probably not over the next week. If it does appear, it’s easy: if you are <somewhere>, then <do something>. If you aren’t , no need to worry yet if at all. Generally the pattern will start with “Interests in <somewhere> should monitor the progress” and once the storm actually spins up more specific actions will be detailed in the forecasts for the storm. The next thing to look at are the two “Formation Chance” lines, for the next two days, and over the next week.

At this point for out example, the system described above doesn’t even really exist yet, the global models were showing a tropical wave moving off the coast of Africa potentially spinning up in to a system with a closed circulation – the first stage of tropical storm formation. Over the next two days there was little to no chance; but conditions were somewhat favorable over the next week as it moves out over water, so the forecaster gives it a 40% chance of becoming a tropical depression. Here’s what it looked like as the sun comes up … can you find it?

It’s a blob of clouds on the north edge of the Inter-tropical Convergence Zone (band of clouds). In fact this storm did spin up and become Tropical Storm Bret.

The stages a storm progresses through are: a potential disturbance that is mentioned in the outlook, then as the forecasts start to converge it will be assigned a temporary ID in the Automated Tropical Cyclone Forecast (ATCF) system, then once it becomes either a sub-tropical or tropical storm, it will be assigned a permanent ID. ATCF ID’s consist of the storm basin (AL – Atlantic, EP – East Pacific (off of Mexico), CP – Central Pacific (Hawai’i), WP – West Pacific, IO – Indian Ocean, and SH for Southern Hemisphere. The basin is followed by a two digit ID number, and the year. The numbers from 90 to 99 are reserved as temporary ID’s and are recycled. These are so-called “Invest Areas”. This allows the computers to start tracking the storm before it is really technically a storm; if and when it does become a tropical system it gets a sequential ID starting at 1. So the first storm of the year will be AL012024, the second AL022024, and so forth.

Often you will see the ATCF ID shortened to just the basin and storm number, leaving off the year – AL92. If that’s not enough, in order to increase confusion and ensure only professionals understand this (seriously, as a hold over from the era when every byte of computer space counted, and since the TC Vitals system uses it), there is also a shorter version of this identification that consists of a single letter and just the two digit ID. So in some places you will see it as “Invest Area 93L” – the “L” being shorthand for AL (Atlantic). Be careful, because in the shorthand system “A” is actually the Arabian Sea, so Cyclone Biparjoy, that made landfall on the border of Pakistan and India, had the ATCF ID IO022023, but the shorter designation was 02A.

Generally it is my policy not to comment on a developing system until it is at least assigned a temporary ATCF ID. There are just too many tropical waves and potential disturbances during the year, and it’s just not worth getting excited about each and every one of them since I don’t really care about clicks. In addition, prior to that time, dedicated models and vortex tracking are not being run, so there isn’t much data to base any discussion on (of course that doesn’t stop some people from rattling on incessantly).

Ok, our clouds out in the ocean have gotten organized, and NHC has started advisories. Aside from restocking your snack supply you ate binge-watching the latest streaming release, what do do? Simply check out the NHC “Key Messages” products, which are nice summaries of the situation. A list of them will appear at the very top of the NHC web page whenever there is an active storm. While I have to check on the storms every hour for research purposes, you don’t: if the storm is more than five days from land, all you need to do is check once a day. As it gets closer, twice a day will do, usually first thing in the morning and then early evening, and start to check in to your local media to see about closings or evacuations. Just don’t get freaked out if they get overly excited – if the NHC key messages start to use phrases like “life threatening” pay attention, but otherwise beware the hype. That said, be aware of your risks. Now is the time to check the FEMA web site for checklists and get ready. It is especially critical to make sure your insurance is up to date – and remember if you didn’t have to buy flood insurance for a mortgage, that doesn’t mean you aren’t at risk of flooding! If you are in a hurricane evacuation zone, you probably need it. And since there is a “lock out” period of 30 days, don’t wait until a storm forms – by then it’s too late.

And, of course, here is where I plug NOAA weather radios. It’s the most reliable way to get alerts and even routine daily weather. During hurricane season your local NWS office will include information on storms, and if one threatens your area issue alerts.

What about tracking? Of course at some point you might want to fix yourself a plate of spaghetti. As, everyone knows the spaghetti harvest is in spring, as this classic BBC documentary from 1957 describes. Just don’t eat it raw, or from a chief who can’t cook or piles on too much seasoning. By spaghetti of course I mean the various hurricane track and intensity models that media personalities and bloggers love to talk about, but more often than not grossly misuse.

Here is an example from a storm from the soon-to-be Bret last year, with a few key models highlighted …

For being a disturbance that wasn’t really a storm yet, this forecast was actually a very consistent picture. Part of the reason for that is the “steering” forces (middle to upper level winds) were fairly strong and well behaved. More often than not track models for developing storms look like squashed spiders.

Before discussing track models and forecasts, I want to make one thing very clear: for the vast majority of people and applications, the only track and forecast that matters is the official forecast from the National Hurricane Center and the subsequent local forecasts from your local weather service office (for the US at this link, click on the map for your local info). If you want to understand what goes in to forecasts or find tracking and the science behind forecasting interesting, fine. But unless you are one of the limited number of actual professional tropical cyclone specialists in the world (and that doesn’t include the TV and internet forecasters for the most part – not criticizing here, but this is specialized work), you shouldn’t be trying to sort out this stuff and make decisions based on the raw track models (in other words, don’t eat the raw spaghetti). So be careful who is cooking your spaghetti, and who is serving it as well! If you use an app or source of some kind make sure the data is timely, and not being filtered or distorted in order to keep you engaged and clicking. I’m suspicious of most apps, even ones that claim they are “free” really aren’t, they are tracking you and selling your data for marketing purposes. Just use the NHC/NWS web sites. They don’t need to track you (the FBI and CIA does it for them 😛 ).

In this case, AL922023 – the future Bret – did not have an official forecast track, just the general area in which the storm may form and move as shown on the seven day outlook. And since there are no “magic words” there was nothing to do or worry about.

However, you’ve been warned, and understand what follows is for educational purposes. Great! Tropical cyclone research and science is really interesting stuff. It is first of all important to understand the various classes of models. The simplest are the “climatology and persistence” models. One of the oldest and most famous is actually called “CLIPER,” for CLImatology and PERsistance. Despite being simple, these models actually do a fair job out to three days or so in many cases. They also don’t need very much information, in some cases only the current location and where the storm was 12 hours ago. This map shows four of these models:

The cyan line is persistence. In other words, if the storm keeps going in a straight line at the same speed it has been moving over the last 12 hours, this is where it will go. The yellow line is from a model known as HURAN, an acronym from HURricane ANalogs. This was one of the first forecast models used by NHC. While it is no longer in use there, I run an updated version of it “in-house” on storms around the world so that I have a single global reference model. It has another advantage, it estimates the uncertainty of the forecast. The greenish line is the CLIPER model run by NHC. This is their reference model for computing forecast accuracy. Again, the only thing CLIPER “knows” is where the storm is, where it has been, and how past storms of similar strength behaved (computed from a regression model). From a forecast standpoint, if you can’t do better than that you are wasting your time. The dark amber line is a modified version of CLIPER that NHC runs, the Trajectory CLIPER.

Statistical/Persistence models are a good reference as to how hard the storm track is to forecast. If the more sophisticated models are close to these tracks, that means the storm is probably being “well behaved” – in other words, it is acting like past storms. If they deviate, it is a good indication there is something “different” about his particular storm.

The second class of models are those based on the global dynamical weather models that are used in every day forecasting. The US model is known as the Global Forecast System (GFS). For historical reasons it is labeled “AVNO” on most track maps (it used to be known as the global Aviation model). The European Meteorological Centre’s Integrated Forecast System model is commonly called the European Model (EMC), likewise, there are Canadian (CMC) models, for Pacific storms the Japan Aviation model is used, and so forth. These models are complex dynamical models that, in the past, were too coarse to fully resolve hurricanes. However, over the last 20 years, they have become detailed enough to become fairly good at simulating hurricanes. In addition, these models can be run in “ensemble mode” to create probabilistic models. Here is what the GFS run looked like.

The primary, “deterministic” run is the blue line. This is the run based on the “best estimate” of where the storm is, and what the atmosphere around it is like. The “cloud” of thin gray lines are various probabilistic runs. These runs are based on trying different initial positions for the storm – especially for a weak, disorganized system, we may not really know where the center of the storm is! Other variables are upper level winds, etc. The orangish line is the mean of the probabilistic runs. By looking at the details of these runs one can figure out what the storm track is most sensitive to, and how good the “primary” run is . HOWEVER these are not “stand alone” tracks – they can only be evaluated in the context of the primary run! So here is a key warning: not all lines on these spaghetti maps are of equal weight or validity! I sometimes see local broadcasters in the Southeast cherry pick the model closest to their viewing area to highlight. That’s outrageous, but sadly more common than it should be.

By comparison, here is what the Canadian model shows for AL92:

The third major class of models are detailed, dedicated, hurricane specific models such as HWRF and successors. I’ll discuss them when we have a more mature storm with some examples to look at, since this post is already too long …

In terms of overall accuracy, each year NHC produces a report discussing how accurate the official and model forecasts are. Generally the official subjective forecast is the best – and is very rarely “worst”, which is something people don’t think about. A good, even great model can get spoofed and create a monumentally bad forecast – humans can often catch those kinds of mistakes. Human interpretation is still needed – so best to stick with the official forecast. But the track and intensity models are the “raw material” that a forecaster uses to create their forecast, and understanding them can help you understand what the forecaster is facing in terms of uncertainty.

As a final reminder, social media is a terrible way to get storm information, Recent changes to Facebook and Twitter have made a bad situation even worse, and sites that don’t pay them to “boost” posts are throttled. They sort and display posts by profitability and popularity, which means an older post with more circulation (but old, possibly inaccurate info) may be seen before later more accurate info. So make sure you check nhc.noaa.gov for current info.

As storms spin up I’ll post more notes on the science behind hurricanes and how we track them, more on the “cone of shame” and other NHC products, and so forth. I hope you found this interesting and useful!

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PS: No, I can’t stand Jimmy Buffet, for anyone who thought there was a veiled Parrot-head reference in the first paragraph. Here’s some serious music for hurricanes and storms 🙂