Tag Archives: Gulf Stream

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Even a Steady Breeze can be (a) Variable

Our wind preference for crossing the Gulf Stream

No, it’s not a new burgee, it’s our wind preference for crossing the Gulf Stream — and some greens and blues can be degraded to yellow and green by left over swell from Northerlies

As I sit here listening to the first heavy rain in weeks, I decided to share some observations about the wind forecast for the Gulf Stream which are better than anecdotal, if not quite statistically robust. What is important here is the thought process rather than the precise data. The central observation is:

How much a ten day wind forecast varies often escapes us, and forecasts of more than two or three days (text or GRIB) just aren’t very useful for spotting Stream-crossing weather windows. These observations neither transfer nor scale to other situations/areas. [All graphics can be clicked to expand.]

  • Days NoticeSince we have been stuck here in our Catch-22, there have been 11 crossable days (blue green and about half yellow — 11 out of 23) — single days sandwiched between bad ones didn’t count.
  • Persistent forecast for each of those crossable days was available 3, 4, 6, 2, 0, 0, 1, 0, 0, 9, 0 days ahead  — or an average of 2.3 days in advance.
  • If the one nine day outlier is removed, the average drops to 2 days.
  • Since we prefer to avoid the yellow days and single days, this drops to 5 crossable days with 2-3 days notice.
  • Crossable doesn’t necessarily mean enjoyable.

variableStare at the picture from a distance. Columns are the successive forecasts. Rows are the evolution of the individual daily forecasts. The last block in a row is the observed wind on forecast day. The open green boxes capture the histories of the evolving crossable windows. One can begin to see windows don’t announce themselves very far ahead.

obspredSo what have we seen as to observed winds and predictions? The best windows (in turquoise territory) are two or more days long — either leaving time for swell to abate, or time to get farther along one’s route — beyond the Gulf Stream. [The convention with each of the charts that capture wind direction is N = 0, E= 90 and S= 180 or -180 which ever was least ambiguous when plotting, and W = -90.

MaxsHow did these forecasts conditions vary with time? Here are the max easterly (N>E>S) and max westerly (N>W>S) directions predicted through the evolution from first forecast to observed wind.

Interestingly, the observed winds seem to come closer to the maximum westerly prediction and the predicted winds come closer to the easterly maxes. I’m betting this is a jet-stream driven observation, Especially since a deep south jet has been a strong influencer lately.  So can one say if the jet stream is well south, bet on the more westerly predictions? Don’t know, but I think I might since the assumption fails toward safe.

rangeofvariabilityBut just how variable were those forecasts (degrees between E-maxes and W-maxes)? The average variability for any given day was over 90 degrees* during the evolution from forecast to observed.

As you can see the data is choppy, and two of the most variable days were associated with a very good window. So wide variability is not cause for writing off a particular day — especially if one is outside the “last two days” zone.

*Somewhat biased downward by short forecast periods or short evolutions at each end of the data field.

varscatterThere are some features to variability that may be useful (or may be more jet stream). Here we can see the greatest variability was strongly associated with observed winds from the W>S (blue). This doesn’t surprise since these winds are themselves the heralds of change — of approaching Fronts.

However, while the predicted wind (yellow) directions seem to lack correlation with variability, the amplitude of the variability is as great as the observed winds. This tells the story — the best wind directions are the hardest to predict. Or, when it’s forecast to be bad, you can be pretty sure it is going to be bad, and when it’s forecast to be good, go figure.

windowtwoThe widest window (25-28 Jan), the one with one day which had nine solid days of notice, how did the variability play out? Through most of the forecast period, only the 27th looked useful. The other three days offered  no notice.

The bottom line. Be prepared and jump when nature says, “frog.”

It Isn’t Always Velcro…

StucknessVero Beach is often called Velcro Beach because a lot of cruisers stop here and go no farther, to include swallowing the anchor and settling in the area. It is a nice place. But some of us get stuck here (bureaucratic SNAFUs notwithstanding) due to the Gulf Stream weather. As far as crossing the Stream under conditions that meet our criteria (Wind direction, Speed and Seas), this is the longest spate of unsuitable weather we can remember. The curve shows the average (from D-10 to D) of all forecast values predicted for a given day. The green bands are the good stuff. The weather has followed the wavy forecast curve almost slavishly — albeit with teases. At least it is good weather for waxing the deck, meeting even more of the nice folks here, and being stuck here meant being here for a potluck with excellent barbequed pork provided by the marina and cooked by the dockmaster — and a scad of yummy side dishes including Janet’s Spinach Balls.

Window Watching

No, it’s not Hitchcock, and no, we didn’t misspell “washing.” We are back into that mode of looking for and at weather windows for running down the coast from Fort Pierce to West Palm (163°T), W. Palm to Port Everglades (186°T) and Port E to West End, BS (058°T).

Window Watching

Click for Detail

These are the things we consider.

thunderTHUNDERSTORMS We’ve been offshore in thunderstorms. We do not consider that fun. If we are there when then they develop or sweep in, we attempt to avoid them. If we are going somewhere where avoiding them is constrained by shorelines and currents, etc, we wait them out. And sometimes we just get clobbered.

rainVISIBILITY Yes we have radar, but radar in the rain can miss the small stuff, and so can we when its raining. Given the congestion (and floating garbage) along the Florida coast, we prefer not to be coasting in restricted visibility.

GSWGULF STREAM WIND We do not get into even the edges of the Stream when there is a northerly component to the wind. Sustained easterly winds push the Stream toward the beach, so we often find ourselves less than a mile off the beach to avoid the heaviest current and sometimes to pick up the counter-current. Even in a south flowing counter-current the swell from the stream makes its way to the beach. So going coast-wise under sail at reasonable speed pretty much requires a due east or due west wind — rare, and usually associated with a recent or impending shift and, therefore temporary. SE-SW winds mean beating, which can add 25% to the time required. If the headwinds are over 12-15 it becomes a slog.

GSWANCHORAGE WINDS Anchoring in West Palm is problematic. It is an unconstrained wind tunnel N-S (long fetch). Winds over 12 mph without a significant E or W component (and preferably E) turn the anchorage into a very lively place and not one to be stuck in. One really wants to do the two legs in two days.

dollarMARINA DAYS  Marinas are expensive whether they offer a good value or not. For most places, the break-even day for daily rates for thirty days vs the monthly rate is between 9-11 days. So paying for a month and leaving between day 9/10/11 and day 31 is the cheapest solution (if you need marina services and access). But pay for a month and have a window come early, and you better hope the marina is willing to drop back to daily billing.

jetJET STREAM  It’s not on the chart, but the behavior of the jet stream is a big deal. When it hangs around the high latitudes and seldom dips south, the weather windows tend to be often and wide. When the jet stream wobbles its way deeply south and often, the windows tend to be less frequent and narrower. That’s what is going on now.

And so it goes, we’ll trade it for shoveling snow and commuting.

 

Crossing Dynamics

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Our sea surface temperature information overlaid on the NOAA chart (click for large), and our track. The swell and wind information were not adjusted for the Stream. So, the 3-4 footers with 11 second periods predicted were 5-6 with six seconds in the core of the Stream. The West winds 5 kts were more NW at 7 in the core. When the wind shifted through NE to SE its speed never increased enough to be usable.

Sailing East across the Gulf Stream from Fort Lauderdale to West end is pretty easy to predict. Go to the beach look at the horizon. if it’s a nice straight line (no humps and lumps) and the wind is fair for the duration, go. Sailing back from West End or Memory Rock is more of a challenge. Looking out at the horizon tells one nothing. Here one has to rely on weather forecasts, swell predictions, and sea surface temperature information. We are able to receive all three through our satellite weather terminal. Generally they are correct in the “core” information, however, there are things one must infer from the products based on outside sources and experience.

Some thoughts:

  • A fair wind for a sailboat sailing is a moveable feast. The crabbing angle required through the trip can vary by as much as 50 degrees. That nice reach on departure can turn into a beat into stacked up swells by mid-Stream. For us it is better to leave the Little Bahama Bank on a run and be reaching by mid Stream. This means a S to SSW breeze…but these can bring squalls.
  • Swells from one direction are highly preferable. With the Stream is preferable. With the Stream is rare. In the Spring NE is common as large weather systems north of the Bahamas as far as Nova Scotia can send long period swells into the southern US coast for as much as a week at a time, and frequent storms can extend this to weeks. They become almost unavoidable. Recognize they will stack up and come closer together in mid-Stream. Plan for it and shape course accordingly.
  • Sea Surface Temperature isn’t discussed much, but on the edges of the Stream it is a current speed map. Each gradation in color away from the core represents some degree of slowing. Where these decelerations occur, small but persistent eddies can form. Don’t be surprised by momentary loss of speed. Also these deceleration zones tend to be seaweed, jelly fish and trash traps, keep an eye peeled.
  • Lastly. Because of the Stream and the general shape of the coast, even though tides from Port Canaveral south don’t have a lot of range, the tidal flow in the jettied inlets can get quite high (4+kts). Riding these currents in is better than bucking an ebb — especially if it is breaking because of a breeze blowing from the ocean. In addition to having a weather window for crossing it is a good idea to have a current window for arriving. Good current windows will last about seven days and can be copied straight from the Tidal Current Tables.

Back in the USA

If last year’s trip back was a D-, this would be a B-.

The dash in the dark from Mangrove Cay (left at 0404) was lit by lightning flashes from unpredicted squalls –fortunately downwind and at a distance.

When we reached the edge of the Little Bahama Bank, a Gulf Stream southerly eddy had set up. We lost a knot to the eddy for about nine miles.

This year the swell were regular and from the NE only. This worked out well till we got to the fastest part of the Stream and the swell stacked up –like last year. We had to sail a more northerly course to stop the rolling. Not as much as last year, only about three hours this time (not all day).

As we exited the Stream’s main wall to the west (where it was supposed to be this time), we encountered seven lesser walls progressively farther apart as we approached Fort Pierce. We did not have this good fortune last year, and it made up for the eddy off Memory Rock.

Also making up for the eddy, we arrived securely on a flood tide — part of the plan, As a result we had a current boost all the way to our anchorage off the channel in Faber Cove. The boost in the inlet had us moving nearly 11 knots in its narrowest section. We motored the entire distance. The wind never went above 5 knots from a useful direction for more than 15 minutes at a time and there were few of those times. Still, we made the trip in only 11 minutes more than our estimate.

On reaching the coast we were disappointed by the dirtiness of the water and air. Before long we smelled scrub fire smoke, and later the AIS showed a dredge making continuous runs offshore to dump dredge spoil. This morning the water is turquoise, but it won’t be really clear until we return to the Bahamas.

We are thankful for a safe and incident free trip.

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