Manual of Barometry (WBAN) Now Online

This is the biggest news of our day, Sept 29, 2015.

While  working on updates to our Barometer Handbook, we found that the 1963 Manual of Barometry (WBAN) has now been scanned and available as a free download.  Apparently it was scanned the year following the publication of The Barometer Handbook.  I would like to think that our promotion of this rare, amazing book contributed to this?

WBAN is the Bible of mercury and aneroid barometers, as well as the basics of measuring barometric pressure... in fact, i wish there were a stronger way to put that description... maybe the Mother of all books on barometers... and altimetry.  It is the monumental work of Louis P. Harrison, but other than a note in the Preface he does not often get credit for it as he was an employee when he wrote it and this was an official "US Weather Bureau" document, numbered WBAN.

(The US Weather Bureau evolved out of the US Army Signal Corps in 1870s. It spent the 1880s in the Dept of Agriculture, and then became an agency of its own in the early 1890s. It moved into the Department of Commerce in 1965 where it resides today as the NWS in NOAA.)

We have had an extremely rare printed copy for many years, without which our work on barometers in general would have been much more difficult, and probably not as thorough.

It is not easy reading; most of the thousand or more pages are pretty technical... in some cases really specific (ie taking into account your latitude and the shape of the earth when computing the weight of mercury and your height above mean sea level), but if you have a question about how to use barometers for getting accurate pressure, then this is the primary source, and we list is as such in our own books.

It also includes one of the first compilations of the fudge factors used to convert observed pressures at higher elevations to realistic sea level pressures, the need of which was first recognized by the American scientist William Ferrel in the1880s. He called this the plateau effect and these constants are still in use today.*  Ferrel also discovered the Buys Ballot law (which was even acknowledged by Buys Ballot himself) and he was first to apply the concept of Coriolis force to the circulation of global air masses, and as it is generally used today,  can be thought of as having invented that as well... though this has a bit more nuanced history.

Find the pdf here:

Manual of Barometery WBAN
What you do with accurate pressure once you get it is discussed in our books Modern Marine Weather and The Barometer Handbook.

Note that the title page calls the book Volume 1, and the Preface refers to what was intended for Volume 2, but to our knowledge, there is no Volume 2 — when you finish this one, I am sure you will be dying for more, but I am afraid this is all there is.

We also have a list of articles on barometers.

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* Ferrel in the 1880s also showed that the outside air temperature needed to make the conversion between station pressure (ie at elevation) to sea level pressure should not be the present air temperature, but rather the average of the present temperature and that of 12 hours earlier.  We did a study in 2013 that confirms this is indeed the case. See Air Temperature Dependence of Sea Level Pressure Conversions

Grib Viewers — New Developments and Special Features

Parts of this article are outdated. We are working on updating it (Aug 1, 2023) and will remove this note and repost the article with a new date when done. *** marks the point we have reached to date.

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Modern weather work underway relies on “grib data.”  This is sailor’s jargon for surface analyses and various forecasts presented in a gridded binary format called “grib.” These are vector data given for each point on a Lat-Lon grid. High resolution data can be as fine as 0.02º (1.3 nmi) between points,  on up to 1.0º (60 nmi) between points. A grid spacing of 0.5º often meets ocean route planning needs, but but for computed optimum global routing 0.25º is common. For inland work we need the best resolution possible.

Wind speed, wind direction, and sea level pressure are the primary datasets needed for planning, but also available and often useful include the height of the 500 mb surface and wind speed at that level, sea surface temperature, precipitation (rate or accumulated), wind gusts, and simulated radar for squall forecasting.  There are also dozens of other atmospheric parameters that could be useful in special circumstances such as humidity at 850 mb level to help identify frontal boundaries, or wind at that level to anticipate squall motions.

Most of this grib data now in use are the direct computer output of numerical weather prediction models, the most popular of which is the US Global Forecast System (GFS) and as of 2023 we can also get surface wind from the ECMWF model.  Thus we are looking at the same data the professionals use to make their official forecasts. The professional forecasters at the NWS, however, also look at other models we might not have access to. They also have more varied ways to look at the GFS data itself.

Thus it is our obligation underway to check the grib data we use, i.e. compare pure GFS model forecasts with the final manual forecasts of the NWS. These two forecasts (GFS and NWS) will be very close more often than very different, but for crucial decisions, or for fine tuning routes as when racing, we must rely on the NWS forecasts, which brings us to one of the main points of this note.

There is increasing  awareness and availability of the National Digital Forecast Database (NDFD) in grib format.  Unlike all of the other grib datasets, this one is actually created by professional meteorologists who are looking at all model predictions before they create the NDFD forecast. The NDFD grib data are the same we see in the NWS graphic maps. The first entry in the NDFD grib set (h00) is the surface analysis, h24 is the 24-hr forecast, h48 the 48-hr forecast and so on. The difference now is we have these every 3 hours, not just as the traditional synoptic valid times shown on the graphic maps. Unfortunately, the global coverage of the NDFD is limited, but for extended US coastal waters we have good coverage (called NDFD oceanic). In the near future we will get easier access to the National Blend of Models, NBM, which has high resolution and covers most of the Atlantic and Pacific. See Modern Marine Weather.

***You can get the NDFD oceanic grib data with an email request to saildocs (saildocs.com), and now we are pleased to see this appear in commercial products like WeatherNet for PC from Ocens (ocens.com). They offer both standard and high resolution NDFD data in the traditional convenience of the WeatherNet interface. Resolution becomes a key factor underway when we are downloading by sat phone or HF radio. The high resolution of NDFD (0.12º) is not needed for open ocean sailing and it can make the files very large. The high res data are best reserved for forecasts near tropical systems or along coastal waters where you might want to detect diurnal changes in the wind closer to shore or within bays.

The other exciting news from Ocens is they offer the ASCAT scatterometer data in grib format through their WeatherNet service.  This wind data is not a forecast; it is the true wind speed and direction measured on the ocean surface as the ASCAT satellite passed over it—normalized to a height of 10m, the same as the GFS winds are.  We only get this unique data about once a day for any one location, but it is a definitive evaluation of a forecast at the time, which we need in crucial decisions.

It is not a surprise that Ocens would be the first to offer this ASCAT grib data as they were indeed the pioneer in this field. In collaboration with the NWS, they offered the first ever grib scatterometer data from the QuickSCAT instrument back when that scatterometer was working. Unfortunately, it stopped transmitting the type of wind data we need in 2009, which was rather before many mariners got to know the power of the data source. So scatterometer grib data is back, and we hope to see more of it.  In the interim, the Indian Met office launched the OSCAT instrument, which provided very good data for a while, but it too has failed.

The latest scatterometer (past) news is the US RapidSCAT instrument on the International Space Station. For a while it provided a broad swath of data (as QuikSCAT and OSCAT did) but it too has been taken offline. We can, however, count on the ASCAT instruments (on satellites MetopA and MetopB), which  are part of the European Space Agency. You can see and access graphic images of all scatterometer data at Ocean Surface Winds Team website  (google ASCAT).  And this data is available in GRIB format from more than just Ocens. The LuckGrib apps (Mac and iOS) have beautiful presentations of ASCAT data and we can get this data directly from NOAA ourselves (see Modern Marine Weather for details.)

Another new development in grib viewing is a low-cost, high-quality grib viewer and data source for Mac and iOS is called LuckGrib (luckgrib.com/blog). It was developed by Pacific NW sailor Craig McPheeters, created in large part while underway in the South Pacific. LuckGrib has an elegant design and convenient interface, with several unique features added to the standard functionality we expect from a high-quality weather tool. Luckgrib has the most extensive source of weather models of any grib app. It also includes a sailboat weather routing option.  At present LuckGrib and Expedition are the only sources of ASCAT data in grib format.

For more background on the important role of grib viewing software and the acquisition of grib files underway in Mariner's Checklist Before Departure.

Special Features of Selected Grib Viewers
There are many grib viewers for computers and tablets with as many different styles of data presentation and unique features, so I have focused here on viewers that can show NDFD grib data, regardless of where the data files were obtained. It is not uncommon to download a file from one source or viewer and then display it in another viewer. We hope to eventually see more sources offering the NDFD grib files, because these are likely to be the best global data available for the waters it covers. It will take a lot more study to decide if a regional model such as COAMPS or NAM might be better for near coastal waters in some cases. Discussions that favor these over GFS (an almost certainly a valid conclusion near shore) may not have made the same comparison with NDFD.
Special features of several grib viewers are shown in the graphics below.

Figure 1. Ocens Grib Explorer for PC showing ASCAT data on the left.  Each of the individual wind arrows is tagged with the valid time of 1743z, Sept 8, 2015. This is a crucial step in the practical application of this data.  Some viewers capable of showing the Ocens ASCAT grib files do not yet include this important time information. Each ASCAT file includes multiple satellite passes (data swaths) and these swaths have different valid times. On the right is the GFS forecast for 1800z for comparison. Also shown is their “route planner” tool that lets us draw a line between selected waypoints and view the wind and pressure at a specific time along that route.  The tiled display is a unique feature of Grib Explorer for PC.

Figure 2. LuckGrib for Mac has a “measure distance” tool that can be used for route planning. It can be marked in intervals, such as  distance run in one day. Then we can move the valid time slider back and forth to watch wind and pressure vary along the route. The high performance of LuckGrib makes this a smooth and informative demonstration of what we might expect. Then we can adjust the route and look again. This is also a convenient way to study and forecast special diurnal winds such as the Coromuel off of La Paz.

Figure 3. ViewFax from Saildocs is a popular grib viewer for PC with numerous special options. Its overall design is very basic, but it includes sophisticated features in a functional manner.  It displays both ASCAT and NDFD data. It has a direct approach to route planning: you select the starting location of your vessel at the h00 time, along with the intended course and speed.  Then each time you advance the forecast time to the new map, the vessel moves to the corresponding location it would have at that time based on the entered speed and course and a pop-up shows the wind and pressure at the vessel. Also shown here is an over lay of the 500-mb surface heights, which offers a good way to evaluate the stability of the surface pattern and dependability of the forecast. See Modern Marine Weather for details.

Figure 4. Expedition from expeditionmarine.com is a premiere sailing performance and navigation program that includes sophisticated weather routing using grib files. It automatically finds the best sailing route to match your polar diagrams, taking into account not just the wind, but also ocean currents and sea state. You also have the option to scale or rotate the grib files to match actual observations.  Though a long established product, we include it as it does show NDFD data and it has a newly enhanced meteogram feature for viewing wind and pressure over time at a specific point. The examples shown illustrate the different behavior of wind shifts on the two sides of a tropical storm. See an expanded discussion of this topic in an earlier post.

(The once popular ugrib viewer also had a meteogram function, but it did not show NDFD data and it did not have any route planning features.  As of mid 2016 or so, Ugrib is no longer available.)

Meteogram display from ugrib.

Figure 5. Coastal Explorer from rosepointnav.com is a popular echart program that also shows grib weather files obtained from other sources, and indeed it will display the NDFD data. Shown here is one easy way for a quick overview of weather conditions. We set multiple range rings on the h00 vessel position at 50-nmi intervals (6h run at 8.3 kts), then we can step the forecast forward with an estimate of where we would be at that time. This program and the others illustrated here will also show ocean currents to help with route planning. The RTOFS or OSCAR ocean current data are readily available in grib format by email request underway.

OpenCPN for Navigation and Weather Work

 This open source program has a vast array of versatile plugins that make it just as valuable for weather work as general navigation.  It also offers a convenient feature of allowing multiple files be opened at once. You can for example, open a standard GFS wind and pressure file together with an RTOFS ocean currents file.

Figure 6. Here is an example of the OpenCPN weather routing plugin finding a good route through the Gulf Stream. The light blue-green is the strongest current.

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.