Sunday, September 1, 2019

BuoyCAMs and Hurricanes, Part 2.

We have an earlier note and video on the use of NDBC BuoyCAMs to watch approaching and passing tropical storms, and indeed detailed info on use of BuoyCAMs in general. We have now renamed that article Part 1, because it is now easier to do what we discussed there, and hence this Part 2.

All the recent TV news about Dorian in the Atlantic led me to look into this again, where I learned of the new shortcuts available now. ( In passing, we have to recommend that the news media should read the Mariners 1-2-3 Rule to realize they were forecasting landfall way too early in the history of the storm, or at least they were doing so without adequate qualifications. At 3 days out the track location* is uncertain by ±300 nmi, and they started calling landfall a week out—not mentioning that the historically most common track does indeed turn north and not go ashore at all. )

To anticipate watching the storm on a BuoyCAM, here is the type of data display we would like to see in Google Earth (GE), and even ideally in our phone versions of GE, and we want this display to be new and updated every time we look at it. This is not a standard GE display; we have to create this ourselves.

Screencap from GE showing NHC track line and cone of uncertainty along with
interactive locations of the NDBC BuoyCAMS. 

When you click a point on the storm track showing in GE you get this type of position report, which will change with each new advisory.

Within GE you can just click a BuoyCAM to see something like this:

This does not tell us too much yet, except there are high seas, which accounts for the misaligned horizons. Get a better view in the computer version of GE by right clicking and choose Open Image.  In a phone version, the image can be tapped then pinch zoomed. To go to the image in the main buoy site just google its number "NDBC 41010," and we can then double zoom to get the max resolution.

Referring back to the top image, we see that this storm could pass right over or very near at least 3 BuoyCAMs as it heads north.  With that said, here is what is new.

We can set up GE now with just a few steps, and it will refresh for us throughout the history of any one storm. The only way we could do this earlier was tweaking the track images individually at every new Advisory, but now the track and cone data are available as KMZ files for both NHC tropical storm zones.

Part 1. Get the BuoyCAM file at NDBC, then on the left click BuoyCAMS, and see on the bottom right of next page a small link to the KML file.

This file when opened in GE (or drag and drop it) plots the interactive buoys on the ocean map of GE. Install once and save; no need to update. This is the easy step. Also this one remains valid for all storms or indeed year round regardless of storm season.

Part 2. The NHC track and cone files are located the NHC site; find them under Analyses & Forecasts / GIS Products menu item.

There are a lot of data on this page. What we want for now is in the top line, by ocean.

A typical link looks like:

With this we see what is new and an improvement, and what remains an issue still calling for custom work.

This file name means:  an Atlantic (AL) storm; in particular storm 05 of the 2019 season, and it is the latest update of the cone of uncertainty data. Storms in the Pacific are labeled EP for Eastern Pacific.

Storm numbers can be determined from the annual lists found in the Archive link at NHC. Find the storm number by just counting down. Dorian is 05 of 2019, Erin is 06. In the EP, Juliette is storm 11. We also need to know these storm numbers to request the text Advisories by email when underway, as explained in our text, Modern Marine Weather. These are the primary and indeed mandatory sources for tropical storm forecasting.

In the previous approach we loaded and georeferenced the NHC image of all active tracks, but then discovered that NHC changes the specs on these images on each Advisory update, so that it was tedious to keep these properly positioned in GE.  This is an improvement in that the mapping is automated so that step is removed, but we are limited to looking at one storm at a time. That is not a problem. The next storm will have a file name AL062019_CONE_latest.kmz.  Note that capitalization matters on these file names.

If we want to see what is going on right now, meaning which buoys are on the storm track in the latest forecast, we can just download the track and cone KMZ files and then open them in GE on our computer or phones and compare to the BuoyCAM locations. But this method will not auto update,  so we cannot just look at our phone anytime later and see the latest configuration.

Here is the tricky part we have to work around.  A KMZ file is just a zipped set of KML files. You can verify this by taking any KMZ file and changing the extension to ZIP and then uncompressing it with whatever tools you use, such as Unstuffit on a Mac, or WinZip or WinRar on a PC.

The NHC KMZ file called "AL052019_CONE_latest.kmz" that looks perfectly generic to the storm, is actually a specific Advisory report on that storm, such as Advisory 37a valid at 2 PM EDT zipped up with the generic name "latest." In short, this file will not update automatically in GE.

So we have to work around this. We know where the file is located that is updated, but we need to automatically fetch that file anew each time we look at the GE presentation. This can be done with a GE menu option called Add / Network Link.

In the Name line you can put anything. Then add the link to to track, as shown, and in the Refresh tab choose hourly and in the View-Based Refresh choose On Request.  Then save and repeat for the cone file. These two files will then auto update each time we open the file, or we can right-click the file name in the My Places list and choose Refresh. I have checked this in both computer and phone and it works. The video at the end here will illustrate the setup in a computer and in a phone or tablet.

That is how we set this up to see the picture at the top of this note in a computer version of GE, which will then auto update.  When you are ready to look at the next storm, either go back to NHC and get the new storm 06 file link, or use the Get Info link on the GE file and change  05 to 07. As it turns out in this case, storm 6 has come and gone (at higher latitudes, but you can still see its track if you like. The next Atlantic storm will be 07.

The other issue that is new as far as I can tell is that the iOS version of GE will now open KMZ files, which are zipped files containing one or more KML files. Unless I was making a mistake last year, they would not open then (only KML), but they do now. Unfortunately, there does not seem to be a way to establish a network link from within the GE phone app, so we have to make it in the computer and then send it to the phone.

Once the track and cone files are in My Places in your computer, right click each and save to your downloads as a KML file.  Then mail these to yourself and open in your phone and assign the attachment to GE. The process is illustrated in the video below. You can then see something like this in a phone, and get the same info you would from a computer display.

In short,  you can tell at a glance where the storm is relative to a BuoyCAM from your phone. The NHC Public Advisories along with new data on the track and cone are updated every 3 hours.

If you want to expedite the process for Dorian (AL storm 05), you can download these three files to your computer and move them into GE, or mail them to yourself and open in a mobile device and copy to GE.




For later storms you can edit the link and name in the Get Info page in GE.

Here is a very nice link to the GOES16  satellite image of the storm.

Demo of the procedures

Pictures captured from the eye of Dorian as it passed over buoy 41004... added Sept 6.

For completeness, I should add that NDBC has a version of what we are doing here on their site. I think this was added after our original proposal from early in the storm season last year.

When you go to the NDBC site you will see the storm icons amongst the buoy icons and if you zoom in you will see the latest track and cone as shown below.

This is almost exactly what we are making for GE, except we are concentrating on the BuoyCAM buoys. If you go to their BuoyCAM display (left side  panel) to limit the view to buoys with cams, then the storm track goes away. They are in a sense pointing out that we learn a lot from the raw buoy data (wind and seas) even when there is no camera, and indeed there are far more buoys without cameras than with them.

This picture also reminds me to add this footnote to an earlier statement on track uncertainty.

* Although the track uncertainty is best thought of as growing at +100 nmi a day, meaning that at 72 hours out the track location is ± 300 nmi, we do not need to consider the forecast any worse than that.  In fact, the models have gotten better and better every year, and we can believe that the center of the storm will indeed stay inside of that cone for the first 72 hr of the forecast, and even more likely be in the center of it than on the edges. If that cone does not go onshore during the next 72 hr of forecast, you can believe the storm center is not going ashore... but that does not mean you don't get the full brunt of the system, albeit the "navigable" side. On land in such cases it is usually the water that causes more damage than wind.

1 comment:

Unknown said...

Nice work David!!! very interesting. I have applied your steps and it looks awesome. I have shared this knowledge with my USCGA shipmates.