Wednesday, June 5, 2019

Another Interactive Test of the Oceanic National Blend of Models

We recently completed a comparison of several models looking for the best extended forecast. The apparent winner in that case was the NBM. There are arguments on why this might in fact be expected to be best for extended forecasts; we will come back to that.

For now we have another, equally crucial test at hand. And in this case it looks like an ideal way to make this test, because the NBM is notably different at 78 hr out than the "competitors," namely GFS, FV3-GFS, and GEFS, and to the best we can estimate it, the ECMWF.

The vessel we are following is moored off of Flynn Reef in the Great Barrier Reef, 30 nmi east of Cairns in Queensland.  He needs winds solidly less than 20 kts to make progress on the last leg of his 9,000 mile row (actual miles rowed, not great circle) from Neah Bay, WA to Cairns AU.

We will use Sat Jun 8, 12z as our test point, which is 78h from the most recent model runs at 06z Wed, Jun 5.  Below are the meteograms for this period at that location that we obtain from LuckGrib.

Note: you can click one of these to zoom it, then subsequent clicks takes you through the set. 

The above is our guess of the ECMWF from The 3 AM shown is AU local time; add 10h to 12z to get local time = 22 LT.

We will add more forecasts, every 12 hr or so. to see how things evolve.

For the moment, we would not have confidence to recommend chances of wind well below 20 on Fri / Sat, but that might change.

========== The next day:  Thursday Jun 6 ==========

Jacob needs winds well below 20 (~ 15 or so) from the SE, or he can also make progress to the west with winds of 20-25 if the direction is more easterly, that is ideally due east (090) or as far south at 110 to 120 at the lighter end of the speeds.

So far all forecasts are 20-25 at SE or even more southerly, which is no go.

 Below is the NBM meteogram for Jacobs present position

The test case we are following here is on Sat, but that wind, even if it pans out, is not a go situation.  On the other hand, we see some indication of winds going more easterly on Friday (tomorrow), still strong however.

The Cairns forecast for now also has indication of going a bit easterly on Friday... whereas all other forecasts now for before or after friday is the ole 20-25 going to 30 at SE.

Friday 7 June

Strong Wind Warning for Friday for Cairns Coast

East to southeasterly 20 to 25 knots, reaching up to 30 knots offshore at times.

We also get this indication of some more easterly from the FV3

A narrow window tomorrow.  This moment is just before daylight on Friday, so we will pass on this info to see what it looks like on the water.

----- added 04z Jun 9-------

In retrospect he did take off Friday, and indeed did get to Cairns, but it was a long hard row. We have not heard from him since arriving, but we do know the winds in the region from Cairns observations shown below.

The NBM from 84 hr out called for 21 from the SE, the actual winds were 23 or so. This is about as close as we could want. In this case the FV3 and the GFS were both over 25, also from SE, so this is not such a conclusive distinction between NBM and FV3 GFS.

On the other hand, a more subtle and encouraging verification is the wind did indeed back around to the east on Friday and called for in NBM and FV3, and that was what triggered Jacob to leave.  The wind did not at all go lighter and we are not sure of the direction at the boat, but it was a long tough row to get to cairns.  

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