Unless noted otherwise, color coded speed scales are in meters/second. Multiply by 2 (1.94) to get knots.

Sunday, January 27, 2013

RTOFS from Angie


Angeline Pendergrass from University of Washington, Atmospheric Sciences Department, Leader of our weather forecast team, has set up this super-nice way to download and display the Hi-Res Atlantic RTOFS surface current predictions relative to a real-time location of the boat.

These should update automatically with latest forecasts as well as latest boat position. Recall these computations are made at 14z and valid starting at 00z. The first is essentially a picture of the currents as best discerned from all Atlantic observations then folded into the model predictions. Later pictures are then pure forecasts. Speed changes at whole knots are marked by a contour line.

There are three vessel positions shown: the latest position, the position 24 hr earlier, and the historic or projected position at the time of the forecast. To see the predicted currents at the present vessel location,  scroll down until the two leading positions overlap.  Also shown are the course made good and speed made good over the past 24 hr.

To view the trends, just click open any one picture, then scroll (mouse roll) though the set to implement an animation of the pattern.



00z Today
06z Today
12z Today
18z Today
00z Tomorrow
06z Tomorrow
12z Tomorrow
18z Tomorrow
00z Day after Tomorrow
06z Day after Tomorrow
12z Day after Tomorrow
18z Day after Tomorrow
00z Three days out



Saturday, January 26, 2013

Sat Jan 26 Oultook

There is a lot of activity in the forecasted currents for the next day or so.  It is certainly our first possible opportunity, but we can't be too shocked if we do not see it. There is here one overview showing the Cape Verdes, and then 3 days of predictions near the boat position.

So far we only see a huge leg to the south which makes it look like an eddy going the wrong way, but in fact they are on purpose following the wave direction now on purpose. We will learn more later.

We see an eddy patch flowing south  in the 00z jan 27 data, but it would have to have been farther north to cause this.  We will have to wait to get more data and then look again more carefully.  It is a fairly fast moving patch of current.

Friday, January 25, 2013

Friday Jan 25 00z currents + Note on the forecasts

Here are currents along with boat track to date (have to look carefully for the track off Dakar). We are still a long way from major current influences... according to this RTOFS data.  Keep in mind that the 0h forecast is as much an assimilated picture of known knowledge as it is a forecast, but because there are no sensors in this near region it does remain a model prediction.

I have just received a very good question about the current data, namely: do we trust the current forecast data yet?

The answer has to be: very sorry to say... but NO.

This is all wishful thinking!!

Many tests of this model for the Gulf Stream region have been excellent, but i think they also tweak the model to work well there.  So we are in NEW territory, which frankly to me is  one of the exciting parts of this voyage.  

At present we are not yet automatically collecting the knotmeter speed from the vessel, so we do not have automated current computations yet.

To figure the current while rowing, we need S from knotmeter, H from heading sensor, and COG and SOG from the GPS.  The set and drift of the current is then just the vector that connects those two vectors.  If those two are the same, then the current is 0.

We always have cog and sog. We can figure that simply from the timed position plots, but if we ever lose either the S or the H, then we have to change tactics.

We lose the convenience of reading the currents live from a spread sheet, and have to ask the crew to stop periodically at a watch change and just drift for a few minutes to report back to us the cog and sog.  When drifting (without leeway) the cog and sog are the set and drift.

We need wind data during that measurement, however, so we can estimate any leeway that might be in place.

Thus without S and H if we see them heading anywhere near a strong eddy we will ask for the tests.

also, of course, if they discover they are going nowhere in seemingly good conditions, we can most likely took at the current prediction to see what eddies might be in the neighborhood and from the shape of these  we can most likely direct them to the best way out of it.  Or if we see prominent favorable current on the horizon, we can do the best to direct them toward it.

For now, though, we just wait till things settle down and all instrumentation is working, and watch to see how things evolve.

--david





Tuesday, January 22, 2013

Currents on departure, wed 1-23-13 11z

Planned departure is 11z on wed.  Currents starts setting them south about 30 miles out, which would be about 21z.  

Monday, January 21, 2013

Currents outlook Wed, Thurs, Fri

No real change. Leaving on wed, the stronger favorable currents further west will have dissipated, so no good ride to look forward to. General picture is not bad, but not favorable as it looks like about 1 kt pushing them south, whereas the goal is to stay on the rhumbline if possible. wind on wed looks like 10 to 15 N-NE, but building to 17 to 18 N-NE on thurs and fri, so definitely getting pushed south. we will get better wind forecasts from the weather team. As we have seen often, the wind tends to go more easterly as they get closer to the cape verdes and beyond.

Saturday, January 19, 2013

Prog for wed, thrus, fri made on previous sat.

This is first real look, but still reaching out into time on this.  Departure is scheduled for wed. currents seem to be in the right direction, but no big rides on the horizon. Note they travel very roughly the width of one grid line per day.  these are 1ยบ apart, but i forgot to label them. islands on the left are the cape verdes.






Thursday, January 17, 2013

Outlook for Jan 21, 2013

Still trying to figure way to automate these presentations on some level...

We use the RTOFS Hi-Res Atlantic Model. This gives data for 144h, so 6 days is the farthest we ca look ahead.  No idea yet how dependable the predictions will be.  As of latest word departure is Wed, the 23, so it will be a couple days before we know what that looks like.  Farthest ahead we can see is 21th, which looks here like light current for first 60 nmi (ie first day) then some lift of a knot or so to the west, but this is a rotating eddy, so we really need the animations, which i am working on.