Sides of a Tropical Cyclone, Part 2 Meteograms.

In Part 1 of this topic, we looked at a way to study the wind and pressure on both sides of a tropical cyclone (TC) using any grib viewing program. There are many such programs available and the method outlined does not require any special features. Any of them could be used.  In this note we look at another way to study this that takes advantage of a special meteogram feature of the navigation and weather program Expedition.

In the presence of an approaching TC, we can judge where we are relative to its path by watching the wind speed, wind direction, and pressure from the perspective of being on one side of the storm's path or the other. In the Northern Hemisphere (NH) the right-hand side when facing in the direction of the storm's motion is called the dangerous side, whereas the left-hand is generally more manageable, at least if some distance away from the center, and it is called the navigable side. Part 1 included background on this and references.

The names are in large part based on the fact that the approaching winds on the dangerous side tend to push you into its path, whereas on the navigable side the approaching winds push you away from its path. The sea state on the dangerous side is also notably steeper and more chaotic.

A meteogram is just a plot of the wind, pressure, temperature, etc as a function of time. Time can be plotted forward (a forecast) or backward, a history.  The latter plots are a nice way to see, for example, that wind direction undergoes a prominent veer at the passing of any front.  Using a meteogram as a forecast we can show graphically the behavior expected on each side of a TC, as shown in Figure 1.

Hurricane Guillermo on Aug  3-5, 2105. The same example was used in Part 1. The background and meteograms are from Expedition, version 10.0.12.

Here we see in a much more direct manner what we discussed in Part 1. The blue stripe in each case marks the conditions we would observe from a stationary position over the day the system approached.  The two side points are about 70 nmi to each side, with all 3 being about 200 nmi off—which before any further discussion we have to say are all three very close to this system.  Such intense systems to not emerge suddenly, or if so, extremely rarely.  In this case we would have had at least 3 days earlier to know where this storm was going to be at this time. Thus how we ended up in one of these positions is an entirely different issue!  In short, we would have to say that we are primarily thinking about rare situations in which we did not have contact with the outside world and thus did not have the official forecasts.  But then, even with that assumption, we have to assume further that we did not have a $200 SW radio on board that would have told us the storm location and motion at least once every hour. Such a radio runs on batteries and is not dependent on the ships power.

Looking at conditions during the blue bar, we see first one important factor.  In all three locations we did not see much interesting at all for the first 6 hr, and that is because the closed isobars of the system had not yet reached us.

Once the closed system reaches us we see the expected behavior. On the right the wind builds and starts to veer. On the left we see the wind backing, but it actually falls off a bit, and in any event this far off the axis it never does build much.  This illustrates the value of getting as far as possible from the center of the storm as it passes.

In all three cases we see the pressure going down as the Low center approaches. There is more discussion in Part 1. The main goal here was to shown this new way of studying this behavior.  As it turns out, we have three very large systems in the Pacific right now, so I will try to grab some data and make a video of the use of these metorgrams.

There are other ways to generate meteograms using online resources, once you know the Lat-Lon and time you want. Most of these must be near live times, however. One example is https://ready.arl.noaa.gov/ready2-bin/main.pl  but I recall others that are easier to use.  I will add them here as i find them.

Commercial Echart Ad is Food for Thought

It is not clear that they have thought through the marketing logic here, which only adds to the challenges we face moving into the realm of modern navigation.

[Recall MacDonalds long term request that we "Put litter in its proper place," which has to mean throw your trash on the ground... else it would not be litter.]

From an August 26 email ad.

If they do indeed make 2,000 corrections per day, what is it they are correcting? 

The true charts themselves are not changing anywhere near that rate, even on a global basis. So this simply means they are mostly correcting their own errors in their own proprietary electronic charts. [*]

Thus we learn several things. Good—these charts are getting better every day. Bad—they indeed do have a lot of errors in them. (See related note.)

So the recommendation we make remains the same. When using electronic charting we are still better off with raster charts (RNC) when available. These are direct copies of the latest official charts, which these days are updated every week at no charge. Then if we want the convenience of some commercial vector chart such as this one in a packaged set of electronics of software program, we can then check it with the latest RNC or ENC.

See www.starpath.com/getcharts.

[*] To be fair, maybe they are not just correcting actual errors but adding new information, to an otherwise correct chart. That would have to  be checked, and evaluated. If the addition is something that is already on the official charts, then is that an "error"? If it is adding something that is not crucial, then that is what it is. 

The reason vector charts (official or commercial) will eventually be our main resource is they offer so many layers of information, and are indeed easy to update, even remotely. Some of the information in deep layers is not crucial often, but could be in special circumstances. 

So the 2,000 updates a day shows they are working on this.  My comment here has more to do with the choice of marketing idea. My first impression was with that many updates, they must have a lot to fix.

Sort of like advertising ones level of experience in navigation by citing all the hurricanes they have sailed through.  I would tend to listen more to the person who has sailed all their lives and never been in a hurricane.

Mariner’s Weather Checklist Before Departure

 It is fundamental to safe efficient weather work at sea that these items be checked off and tested before departure. Having it all onboard without prior testing does not count!

(1) Barometer. This is key instrument to any ocean or coastal passage. Check it over a large pressure range using free service at www.starpath.com/barometers,  or just interpolate the isobars to get the correct pressure for your location at the synoptic times from unified map at http://www.opc.ncep.noaa.gov. For electronic barometers, you likely have an excellent one in your phone. Use our free marine barometer app, and read the help file that comes with it—a short course on barometer usage. We have extensive notes on barometers.

(2) Wind instruments.  To measure apparent wind speed and apparent wind direction, and they should be calibrated.

(A nice backup to both of these is the small handheld Kestrel 5500. The barometers on these that we have tested have been excellent. It is easy to check the windspeed driving along in a car holding it out of the window. Using one of these to check your onboard instruments, remember that wind at the masthead can be notably different from wind on the deck.  Might have to take it up the mast.)

(3) Calibrated knotmeter and magnetic Compass, and calibrated heading sensor.

(4) True wind from Apparent solution. We need some procedure to convert apparent wind to true wind that is well tested and practiced. This can be done within the wind instruments themselves or some other electronics box they plug into, or it can be done by inputing the data to a computer and computing it there,. Or it can be done by hand with a calculator, which is best done with one that is programmed to do this. There are numerous smart phone and computer apps for this.

(5) Laptop computer. There are certainly ways to do safe weather work without one, but  a computer makes everything related to weather very much easier, more versatile, and better. I would consider it a required item since so many of our best resources are obtained via the computer. In fact since computers are so inexpensive these days, it is not even unreasonable to set up one with all your nav and wx software and connections and then just clone it to another one which you take as a back up.  For PC users, Acer has several very good low cost laptops. Mac users know what is available.

(6) Communications.  This would mean either a sat phone or an HF radio with Pactor modem.  The sat phone is definitely easier, but day to day usage is more expensive.  HF radio work could be near free once set up, but the investment would be notably more than a sat phone to set up from scratch.  It would be nice to have both, that is if the boat is already set up for HF radio then add a sat phone for convenience and dependability.  If not set up already, it would be harder to justify the expense compared to sat phone only.

There are these days all sorts of other communications options, from satellite broadband to systems that connect everything on the boat wirelessly.  However, the basics are in item (6) and they should be there regardless of the other luxuries.  In a sense, the more you have the more that can go wrong, so you want to be able to pick up the sat phone and make a call, or plug it into your computer and send an email.

(7) Software for email. We need software to send and receive emails with attachments… with no restrictions on what we say or include, which rules out the basic ham radio programs. There are numerous options. Airmail from Saildocs is one. Ocens, Xgate, or UUPlus are a couple other options. Each has unique services or features; the prices vary somewhat, but not a lot.

With (6) and (7) in place you can send and receive emails and email attachments by satellite phone.  All of these offer the option in setup to switch between communicating by sat phone or communicating by Internet.  Underway you will use the sat phone, but once in a harbor with Internet, you switch to that.

On the other hand, for getting set up and tested before departure you would also primarily use the Internet connection, but it is crucial that you just spend the air time and do several transfers by sat phone long before departure date. You want to be 100% certain that this system is working, i.e. send and receive emails with attachments. Turn it on and off, computer on and off, reboot, close all, start again, switch back and forth between sending by sat phone and by Internet, try multiple types of files (discussed below), etc. The main point is to be sure this is all working well before leaving and that you have used it for a couple of weeks at least getting your weather information, as outlined below.

Added in June, 2022: We have preached this last point for 15 years, but still find that this is not always done, and very often leads to no communications or weather data underway. This is an avoidable, serious error.  There are many things to get done before leaving, but this one has to be at the top of the list. It is a pity to not have excellent communications at sea these days with all the wonderful options we have. Please do not add another example to the notable list of mariners who did not follow this advice and suffered for it. Beyond weather routing, if equipment fails or a medical emergency occurs, we need communications. Even in a yacht race where outside "tactical assistance" is prohibited, it is still perfectly legal and good seamanship to get help repairing a failed instrument or system.  It is also not uncommon to use up tons of air time on a handheld sat phone getting instructions on how to implement the email system in the computer, which should have been done before departure.  It is then also a sad time to learn that you bought the equipment from the wrong seller and they do not know enough to help you!  So on the prep list is buy from knowledgeable dealers who can help you... and get that help before you depart.

(8) Software for GRIB viewer. Many, if not most, echart programs include the option to overlay GRIB formatted weather data right on the echart you are navigating with, but these are sometimes limited, so supplementing that with an app that can display and analyze weather data is crucial.

I assume you will have some echart program in a laptop for navigation that is tracking your GPS position. Almost any one of these will show grib files for weather analysis. ( If this has not been planned, i.e. you have a console unit from your navigation electronics doing this tracking, then you may want to consider adding the laptop or tablet navigation option. You can do very much more with your own echart or weather app in a laptop than possible with any of the packaged units which are then restricted to just the chart formats they provide as well as limited navigation tools.)

In any event, it pays to have a stand alone grib viewer in your laptop if you do not have one in your echart program. There are numerous options. For the PC there is Viewfax from Saildocs, qtVlm, Expedition, and many others. For the Mac there are fewer choices, but LuckGrib for Mac or iOS remains at the top of the line for both data delivery, display, and analysis.

(9) Source for grib data. Establish and practice with some source of grib weather files. Saildocs is an excellent source. Many of their download options are included in a convenient Viewfax utility called “Get Data”, but they have much other data that are not listed there that must be obtained by email request to saildocs.  LuckGrib has the state of the art data selection, including ASCAT measured satellite winds and OSCAR currents, which others no longer include. See our Weather Course for details.

And again, it is crucial to download some of the files and learn to use these forecasts before departure.

(10) Text forecasts. Don’t forget the text forecasts. Practice receiving by email the crucial text forecasts, as outlined in another note in the references below.

(11) Seawater temperature. When sailing in the Gulf Stream or any other strong current system, or when sailing in the tropics in general, it is extremely valuable if not crucial to have a through-hull seawater temperature measurement, or some other permanent way to continuously read and display seawater temperature.  For ocean currents the water temperature marks the boundaries of various features, and for the tropics the water temperature is a measure of TS development, i.e. hurricane formation usually require seawater > 80º F.

References:

High Seas Forecasts and Tropical Cyclone Alerts by Email Request

Weather by Satellite Phone

Modern Marine Weather

Barometer Handbook

Mariner's Pressure Atlas

Sailor's Logbook

Starpath online course on Marine Weather

 

 

High Seas Forecasts and Tropical Cyclone Alerts by Email Request

In several articles we point out that standard analysis and forecast maps of tropical systems do not have nearly enough information on them to make weather routing decisions.  We need more information. One approach is to download a GRIB formatted numerical prediction. The GFS is the most popular; the NDFD would be superior if that were available to your waters.

With or without these GRIB files, it remains valuable to also obtain the text forecasts from the NWS, in part because the GFS—or any one single model—can sometimes be quite a bit off on the tropical system intensity.

We have three basic text reports that might be of interest: high seas forecasts, high seas discussions, and tropical cyclone alerts. The basic ones we need to supplement the maps are the forecasts, and these are easy to get.

In principle we can get all of the text reports we need from the NWS FTPmail service, but this requires a very specific format and list of file names. An alternative is the excellent services of Saildocs, which have proven very dependable and versatile; it is relied upon by thousands of mariners worldwide, so we will limit the source to this one.

The eastern half of the Pacific Ocean is in the IMO GMDSS forecast zone called Metarea XII; the western half of the Atlantic Ocean is in Metarea IV. 

To get text report and forecast for Metarea XII (North Pacific)

send an email to query@saildocs.com with the body of the text blank except for 
send met.12  You can put anything in the subject line, which can serve for finding the mail for a repeated request. Be sure there is no signature or other text or graphics in the body.

This is all there is to it.  Try it here.

You can also subscribe to this request to have it sent to you automatically every day.  Send a blank email to info@saildocs.com for details.

For other metareas, use these Saildocs abbreviations

Code	Metarea description
Met.1a	North Part of North Atlantic Ocean (High Seas)
Met.1b	Northeast Part of North Atlantic Ocean (Offshore)
Met.2	East Part of North Atlantic Ocean
Met.3e	East Mediterranean Sea
Met.3w	West Mediterranean Sea
Met.4	West Part of North Atlantic Ocean
Met.5	North Part of South Atlantic Ocean
Met.6n	South Atlantic Ocean North of 60S
Met.6s	South Atlantic Ocean South of 60S
Met.7	Southeast Atlantic Ocean + extreme SW Indian Ocean
Met.8n	North Indian Ocean
Met.8s	Southwest of Indian ocean
Met.9	Red Sea, Gulf of Aden, Arabian Sea, Persian Gulf
Met.10ne	Northeast of Australia (Pacific ocean)
Met.10n	North of Australia
Met.10w	Southeast of Indian ocean
Met.10se	Southeast of Australia (Pacific ocean)
Met.11ior	West part of the North Pacific Ocean (from China)
Met.11por	West part of the North Pacific Ocean (from Japan)
Met.11sW	West part of Pacific Ocean, 0-12S 90E-142E approx
Met.12	East part of the North Pacific Ocean
Met.13	Northwest of Pacific Nord and part of Arctic waters
Met.arctic	From SW corner 67N, 44E to NE corner 80N, 165W
Met.14s	South Pacific south of 25S
Met 14trop	South Pacific north of 25S
Met.15	Southeast Pacific
Met.16	Southeast Pacific between 18S and 3S)

We can also see these reports online two ways. Directly from the IMO see
http://www.jcomm.info/index.php?option=com_content&view=article&id=105&Itemid=37

and we have similar reports from the NWS from this folder:

http://weather.noaa.gov/pub/data/forecasts/marine/high_seas

The files matching metarea XII and IV are  north_pacific.txt  and  north_atlantic.txt

If you are sailing across one of these oceans, you would want to set up a schedule with Saildocs to send you the text report at least once a day, automatically.  This will supplement your maps and GRIB file weather analysis.

You can of course get this information from the HF radio. The USCG broadcasts voice versions of the above forecasts 4 times a day. See http://www.nws.noaa.gov/om/marine/hfvoice.htm

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Any of these services that might potentially be used underway 

should  be thoroughly tested before departure. 

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