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Old 04-08-2020, 08:04   #61
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Re: What weather information makes you take action when offshore?

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Originally Posted by s/v Moondancer View Post
We left Guam heading north for Japan and there was absolutely nothing on the satellite weather systems to worry about. Two days later and 250 nm north the satphone gribs showed a cat2-3 two days behind us and heading straight over our course!

My wife immediately said, "Saipan looks nice" and we changed course 90 deg to starboard!

Pays to have a good coms system, we would have been one of those boats that just disappeared and good to have a real mariner as a wife and partner.

Phil,


What exactly did you see there that you call a 'cat-2'.


Gribs do not show cat-2 anything features - you will see winds, maybe in the spiral form that may suggest something, but I cannot recal ant text data in gribs, nothing that pops up as a 'cat-x'.


???


Do you mean you interpreted the grib data as a 'cat-2' or do you have onboard a software that does that? If so, what is the package name?


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Old 05-08-2020, 13:11   #62
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Re: What weather information makes you take action when offshore?

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Phil,


What exactly did you see there that you call a 'cat-2'.


Gribs do not show cat-2 anything features - you will see winds, maybe in the spiral form that may suggest something, but I cannot recal ant text data in gribs, nothing that pops up as a 'cat-x'.


???


Do you mean you interpreted the grib data as a 'cat-2' or do you have onboard a software that does that? If so, what is the package name?


barnakiel
I can’t speak for them but pretty easy to look at the GRIB data and see if the winds are with in the Cat 2 range etc. Of course, from our perspective, any cyclonic activity worthy if a category is worth avoiding.

Always nice to use the synoptics with the GRIB models (plural on purpose) as more interpretation from a real meteorologist and details on the front type or category of storm but they are not all as good as NOAA’s so sometimes GRIBS are as good as they get despite their shortfalls.
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Old 05-08-2020, 13:23   #63
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Re: What weather information makes you take action when offshore?

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A graphic demonstration of one of the shortfalls of gribs. The computer models make necessary assumptions that simply don't reflect the real world. Accordingly we don't see cold fronts (or their wind shifts) and deep, compact cyclonic events get smoothed over. Further you see only one model without the benefit of all the other data meteorologists use to generate synoptic charts: other models, ensembles, balloon data, satellite imagery (visual, IR, radar), VOSP, etc.
Very much agree synoptics are the gold standard but I still like to also use GRIBs in conjunction as sometimes you see things that may or may not happen before they appear on the synoptics. For example in the Marshall Islands one time an intense low bordering on a TRS was showing on GFS but not ECMWF and not at all on the weather fax. When we downloaded the discussion on Saildocs we could see that the meteorologists were watching the potential system but not with enough confidence to put it on the weather fax until the next day. The extra day of warning, even if potentially a false alarm, was welcome.

Concur the GRIBs are not as good as showing cold fronts as weather maps but we usually also download precip on the GRIBS to show where the frontal patterns are.

One advantage having upgraded to the Iridium Go and Predictwind a few years ago is we can be more greedy in our downloads covering a larger area, greater granularity, more parameters and multiple models. In areas with good synoptics we also use the Go to download synoptics and satellite images from FTP sites rather than use our old weather fax.
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Old 05-08-2020, 13:40   #64
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Re: What weather information makes you take action when offshore?

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When we downloaded the discussion on Saildocs we could see that the meteorologists were watching the potential system but not with enough confidence to put it on the weather fax until the next day. The extra day of warning, even if potentially a false alarm, was welcome.
At the risk of sucking up a bit, it sounds like you are an above average consumer of weather information.

NOAA and UKMET both show the forecaster in the title box. I don't remember about DWE. I keep track. Some forecasters only put in what they know is there and some put everything they think might be there. I like the latter guys. As you say, I'd rather be prepared than surprised. That means sometimes yesterday's 48 hr forecast is more useful than today's 24 hr forecast.

I look at GriBs if I can get them as a supplement to synoptics. If I have to make a choice, synoptics everywhere except the mid South Pacific where there aren't any. *grin* As you say, multiple models can be informative. Same reason I look at 500 mb charts. Also RTOFS and OSCAR are great tools.
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Old 05-08-2020, 14:15   #65
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Re: What weather information makes you take action when offshore?

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I can’t speak for them but pretty easy to look at the GRIB data and see if the winds are with in the Cat 2 range etc. Of course, from our perspective, any cyclonic activity worthy if a category is worth avoiding.

Always nice to use the synoptics with the GRIB models (plural on purpose) as more interpretation from a real meteorologist and details on the front type or category of storm but they are not all as good as NOAA’s so sometimes GRIBS are as good as they get despite their shortfalls.

I always use both (at work) but sailing I often have only one.



Perhaps the new Musk gadget will bring us somewhat more accessible networking soon.


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Old 05-08-2020, 14:23   #66
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Re: What weather information makes you take action when offshore?

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Originally Posted by Auspicious View Post


(...)



synoptics everywhere except the mid South Pacific where there aren't any. *grin*


(...)



I think also in the Indian the coverage is very patchy iffy. Remember out of Aus there was a good coverage towards maybe half way, but beyond there was a big black meteohole. RSA service was mickey mouse - including at least one time receiving a wx fax containing data I think 3 days old.


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Old 06-08-2020, 08:06   #67
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Re: What weather information makes you take action when offshore?

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At the risk of sucking up a bit, it sounds like you are an above average consumer of weather information.
Or just a risk averse weather geek ...
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Old 06-08-2020, 11:19   #68
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Re: What weather information makes you take action when offshore?

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Or just a risk averse weather geek ...
Guess we are all risk averse.
The question is what is really practical for the typical cruiser with 1-2 crew on board at remote areas. The equipment is not the issue, but the knowhow, deep experience and time to analyze all sources of data and get into a practical decision are all indeed impressive!.
All that, vs., say, PredictWind, IridiumGo and in shore friends support (if possible) and alike are probably what the most of us can plan on - just to be practical and as risk averse.
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Old 06-08-2020, 11:42   #69
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Re: What weather information makes you take action when offshore?

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All that, vs., say, PredictWind, IridiumGo and in shore friends support (if possible) and alike are probably what the most of us can plan on - just to be practical and as risk averse.
I simply do not agree. PredictWind is just gribs. Untouched by human hands. No consideration of alternate models. No ensembles. No overhead imagery. No VOSP. No discussion from professionals (OPC, NHC, UKMET, DWE -- not the little guys, some of whom are my friends).

Time is a red herring. I spend 15-20 minutes in the morning on weather while I'm drinking coffee. It takes me longer on boats with only gribs because I have more data and less information. I may spend a few more minutes in the evening in case the day's dataset has changes. Change means instability and therefore uncertainty and therefore risk. Do you compare today's gribs with yesterdays? Today's 24 hour forecast with yesterday's 48 hour forecast? I do, and with synoptics it takes seconds. Granted I'm faster now traveling with a multi-head computer but I've done it for years on just a laptop.

Pushing decision-making offboard is an abrogation of responsibility. Turning decisions over to computers is in my view foolhardy.

Gribs are at best a supplement to real forecasting, and at worst they are misleading. Iridium GO! isn't relevant. You can get synoptics over a GO! as easily as from weather fax (although why you would want to is a question). Satellite services are generally easier and look something like the cell phones we're all comfortable with. They don't work like cell phones. They are more fragile, slower, and getting the data to a meaningful computer is more complex than other technology. Starlink may change that but you can't buy Starlink yet and we don't know how fast it will be at sea level or what the price points may be.

People are going to do what people will do. That doesn't make those decisions well advised or indeed practical.
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Old 06-08-2020, 12:53   #70
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Re: What weather information makes you take action when offshore?

Since we began to do ocean crossings in 1998 we have used SSB to receive weather information, starting with WEFAX images, on the laptop. The images we preferred originally were satellite photos and synoptic charts. By 1999 we learned how to receive grib files and we depended heavily on them.

For the next two decades we continued to obtain our weather in this way, augmented by highseas forecasts over SSB and textual weather forecasts received over SSB into the laptop. There are a multitude of weather info choices on Saildocs and there are choices of weather models and options for Grib files.

Using saildocs we have received text versions of several webpages of weather information, such as NOAA Tropical Weather Outlook. These sources give us the big picture and warnings.

Listening to other vessels check in on the radio nets we get reports which we can compare to the overall pictures we've received by fax and gribs.

Finally, a good weather eye outside and watching the barometer helps us notice oncoming local events.

We have eschewed all the other technical equipment based solutions and shore based weather routers. Our system is a bit backwards but we get the benefit of the latest models and forecasts in a simple and reliable way.

We have always done our own weather forecasting.

This little gem was not on any forecast:
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Old 06-08-2020, 15:23   #71
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Re: What weather information makes you take action when offshore?

What weather did you get on the other side of this cloud?


I am asking as we got an identical formation when sailing below Madagascar and towards RSA. I took all canvas down, lashed down the hatches, etc. .... and waited ....


To my biggest surprise, the weather behind the cloud was benign and indifferent. (sic!)


So I am wondering if the same cloud formation can mean more than one kind of wx event.


And where did you take this image?


Cheers,
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Old 06-08-2020, 15:26   #72
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Re: What weather information makes you take action when offshore?

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What weather did you get on the other side of this cloud?
I can't speak for wingssail. In my experience that looks like a front. What that means depends on the pressure and temperature on each side. If the differences are small, you don't get much. If they are big you'll see a big wind shift and potentially squalls.
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Old 06-08-2020, 15:56   #73
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Re: What weather information makes you take action when offshore?

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What weather did you get on the other side of this cloud?

I am asking as we got an identical formation when sailing below Madagascar and towards RSA. I took all canvas down, lashed down the hatches, etc. .... and waited ....

To my biggest surprise, the weather behind the cloud was benign and indifferent. (sic!)

So I am wondering if the same cloud formation can mean more than one kind of wx event.

And where did you take this image?

Cheers,
barnakiel
This was indeed a front. It occurred between Thailand and Indonesia (Sumatra). The short story and chart is here: <Wingssail Images-Cruising Photos from Around the Pacific>

The wind, Westerly, increased to over 40 (we've seen worse). We'd stuck the jib before it hit and ran off thinking it would pass in a few minutes. It did not. After several hours of flying under main alone towards an unknown and unseen Sumatran lee shore, we turned back upwind and slowly waited it out. The wind died off around midnight, 10 hours after the passage of the front.

Funny thing, I was taking photos, oblivious to the danger, when Judy came on deck and yelled, "Jesus Christ, we're going to get hit, get the jib down!"

This photo shows what it was like after the front blew over us.
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Old 06-08-2020, 18:04   #74
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Re: What weather information makes you take action when offshore?

There has been a lot of good information mentioned on this thread. I have been passaging since 2003 and my route planning method hasn’t changed in that time. FWIW -- First I use OpenCPN on a laptop together with a pirated copy of the CM93 worldwide charts for route planning. A copy of the charts were given to me by a Danish single-hander I met and at the time, I didn’t realize they were pirated....honest! (I am sooo ashamed to be still using them!).

Second, I download gribs from Home Page (free) for the region I am passaging. I have used both SSB and Iridium phone for this task. I don’t have an IridiumGo but assume it has the same capability. I typically get 12, 24, 36, 48, 60, 72, 96, 120 hour forecasts at a 2 degree grid spacing, Wind speed, Wave height and Pressure. I display the grib using OpenCPN which overlays the weather on my plotted route and allows me to see (interpolated of course) wind speed, wind direction and wave heights along my planned route. I also download NOAA’s offshore forecast for the region I’m in. There is little point in downloading every few hours since these forecasts are only re-computed every 12 hours or so. As far as I am aware, all of these other weather services are based upon the same models that you can get for free from the Home Page website. You can select which model you want to use but I’m not going to go too deeply into that here.

Third, If you are close enough to shore to get cellular service, the Windfinder forecasts the wind-surfers all use, are quite good, especially if you are trying to pick a window to go “uphill” against wind and wave.

Fourth, I have used commercial weather services in the past but in truth, what they have provided mostly is a warm fuzzy feeling that “someone” is watching over us. On more than one occasion, I have chosen to ignore the recommended routing and make my own decision based upon my own evaluation and risk assessment.

Finally, if you have radar, use it. It’s the best tool for evaluating squalls, their speed, direction and intensity. If you see a big, solid band of light moving at speed towards you on the display, take the sails down and turn the engine on. Easy enough to put the sails back up once you find out what is on the back side of those clouds.
Fair winds,
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Old 08-08-2020, 12:56   #75
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Re: What weather information makes you take action when offshore?

The approach of a weather system is difficult to interpret (at least it is for me as I haven’t made weather forecasting a science on my boat) and the presence of squalls that are short-lived are generally not evident on GRIBs or synoptics.

The thing is when does a squall become a weather system? I did a passage NZ to Fiji two years ago and experienced a series of line squalls about three hours apart throughout a day. Winds of 40kn for an hour or two, driving rain, then back to 15-20kn and sunshine with the next squall visible on the horizon. But then in the early evening, a squall that looked like all the others approached and windspeed went to 40+Kn but it stayed with us through the night and most of the next day. It was great as we had it on the port quarter with just a reefed main up doing 9kn. But then it was followed by total calm for 12hrs.

I’m kind of inclined to look at GRIB-derived forecasting (PredictWind) over quite a wide area and use that to “predict” my expectation of coming weather. After all, the computer modelling was designed by meteorologists who hopefully know their stuff and I have had a great deal of success applying the info to obvious signs on the boat (the sky, the sea state, the barometer).

The only time in recent years that I depended on a shore-based weatherman (one of impeccable reputation), we got caught in an unpredicted squash zone that gave us sustained 80kn and 40ft seas for 36hrs. And I’m quite sure he used synoptic charts for his forecast.

Whilst home, I often download PredictWind forecasts for our sea area then watch the actual weather as a comparison and I must say, the level of accuracy is well within an acceptable range for me.
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