Saturday, July 2, 2016

Vic-Maui Race Day 1, 2, (3) Winds

The Vic-Maui race in 2016 has 4 starts, each at 930 am on July 9 to 12.  This note is about available wind data during the first few days of the race.  This would also, of course, apply to anyone sailing out the Strait, headed to Hawaii on any date.

We have gained fresh experience recently with regional wind models while working on the R2AK planning and analysis for our fast friends on MAD Dog. The best wind data available for the start are commercial products, and as such are only legal up to the starting gun. These winds are the main topic at hand, but once underway we must rely on free pubic data, which would include:

GFS (28 km),  available all the way to HI, but not too valuable till out in the ocean.

NAM (12 km), available from the Continental US run (CONUS) that goes about half way across and then again in HI region, but the NDFD would likely be better for that.

NAM CONUS coverage

NDFD (3 km). This is almost by definition the best free, public data, but it only goes out to Lon 133º W, and then is available again in HI, as shown below. It can be useful in the Strait as well. See The National Digital Forecast Database.  This is not strictly "model forecast," as any one of several models might have dominated its production on any given run, but rather it is the digitized forecast of the NWS using whatever model or input they chose to use.

NDFD HI coverage

All three of the above are available from saildocs underway.

For the start the free hi res data are the NDFD (above), but the best data is likely to be one of these:

HRRR (3 km).  This (High Resolution Rapid Refresh) model is updated hourly,  but only extends out 15 hours, and to get all 15h you must download 5 files. It is available from the Ocens WeatherNet app. Ocens offers short term accounts for this access as well as a 3-day free demo.  I am proud to have taken part in convincing our friends at Ocens to offer the grib format of this important data.  In the R2AK planning, there were several cases where this was hands down the best forecast. For leg one, it remained correct, despite all other models being wrong, as well as the NWS and CND text and VHF forecasts being wrong.

HRRR data. 15h of forecasts in 5 files. Goes north to Cambel River... ie perfect for the R2AK run to Seymour Narrows.

With that said, that is not the only data we used and benefited from.  We also used the

PredictWind PWC/G (1 km, 8 km). The smaller regions in the Strait are 1 km; the coastal regions are 8 km. See

This product has several advantages. First it is super easy to access in Expedition or by email, and the 1 km hi-res models extend out 36 hours,  compared to 15h with HRRR.  They also have a convenient (Mac or PC) app called Predictwind Offshore that lets you either request and look at the data online, or what is often more convenient, it will prepare a template request that you just email to them when you need an update. The larger regions of 8 km are 390 kb each, the smaller regions of 1 km data are 250 kb each.  The 8 km (also hi res) goes out a 7 days—like the lower res GFS, more or less into the realm of the unknown. The navigator is of course going to say that in the ideal world you have both the hi res from PredictWind, and the HRRR from Ocens.  Maybe someday saildocs will offer the HRRR.

Predict Wind also has a weather routing/optimizing feature that seems to work pretty well. You can also use custom polars for the analysis.  For inland waters, however, it does not account for currents, which leaves Expedition at an advantage for that— but I should add here, if you do not have good current data, then you could be better off without using currents at all!  PW does offer and use ocean currents for the ocean routing.

UW WRF (1.3 km).  Unique to our local waters, we should always remember the UW WRF model, which is likely as good as any, but only available as a graphic format;  there is no grib format. The  model is run every 6h and data would typically be 8+ hr old when we get it, and indeed they might not be there when you want them. This is a public service of the UW Atmospheric Sciences Dept.,  with no guarantees.

UW WRF model, run every 6h extends out 60h.

 In fact, this model could be the best model for the region, but it is not updated often enough to compete with the HRRR, which is updated with all the latest actual wind observations every hour.  The HRRR model actually has wind forecasts every 15 minutes, but Ocens has not included that option.

Nevertheless, it is worth printing out the UW data before the start, and with a good connection offshore, perfectly legal underway.  You can figure out how to request the image forecast underway using saildocs—to be added in a future post.

Looking ahead, two articles on the horizon are (1)  the use of a plugin for OpenCPN that *very neatly* lets you load weather maps into your navigation program. We have  been struggling on ways to do this, and simply did not know about that option.  Expedition can do this nicely. And (2) also still working with OpenCPN, which we use in our classes, there is another plug in for OpenCPN that does weather routing!  I have no idea how this works yet; we need to study that and report on it.

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