Faith in Weather Forecast?

[deblen]

Originally Posted by Dockhead

Ken, in smaller bodies of water with a lot of land influence -- there is a lot of chaos in the system, and a lot of chaotic events which can't be forecast, especially in summer. Land creates convection, especially in summer, creates sea breeze and land breeze, creates summer thunderstorms, and creates katabatic winds, all of which is different, and far less predictable, than gradient wind which is create by larger systems and basic pressure differences. The weather models work amazingly well with gradient wind, and so further from land and in larger bodies of water, the forecasts are much more reliable.


But you know the old sailor's weather adage -- "Long foretold; long last. Short notice; soon past." This is of crucial importance to us -- a sudden blow caused by convection or other land effects cannot create a dangerous sea state offshore (what you might get in harbor entrance, over bars, tidal races, etc., may be a different matter). No amount of wind, blowing for less than a few hours, can be really dangerous for a strong cruising boat like yours. Just heave to or run off and let it pass. To get a really dangerous sea state, a lot of energy has to get transferred into the water, over a large geographic area and over a longer period of time.

So what that means is that we don't actually have to worry all that much about unforecast, land-influnced weather events -- dangerous weather events are those that create dangerous sea states, and you can always see these coming pretty far in advance. These events are created by large weather systems and big pressure differences, and you always see that kind of thing at least a couple of days ahead.


Here is what to be afraid of:

Attachment 128727


It's hard to photograph sea state, but this is higher than our first spreader (which is 10 meters above the deck), blotting out the sun and blanketing the sails in the trough. This occurred last year in the North Sea, building up slowly after 24 hours of a F9. Even these are not actually dangerous, except that they are already big enough for the tops of them to start to fall off:

Attachment 128729


So pretty soon you are steering around the breaking ones, praying, and steering cross-ways down the wave faces trying not to speed out of control.

Unfortunately we got hit by one of these, and it was like having a building collapse on you. Knocked us down. An experience I don't want to repeat.


But this was not unforecast. This was a big weather system which was foreseen even a week ahead, and which lasted for a number of days. On the day we sailed, it was supposed to be F8 for three days, which would have been ok as we were sailing downwind, but after 24 hours of it and then building to F9, that was already too much, in the Atlantic Ocean with 3000 miles of fetch.

Right on!!
Beware of shoal water < 50 fathoms with very deep water offshore from it.
All that deep water is trying to climb up on the shoal bottom,driven by wind & tidal current. The result is 3 or 4 sided pyramid shaped seas-very easy to fall off sideways or pitchpole. / Len

[belizesailor]

Originally Posted by meirriba

...

As to reliability you must take everyhing as probabilities. I keep on file a forecast received mid-Atlantic during ARC2003. It warned of a 'major tropical event, gusts over 80kn'.
The actual wind was 15-20kn.

I think a lot of folks miss that concept too, all models are just forecasting probabilities (the heart of any simulation model)...not certainty.

For forecasts that have associated commentary by the forecasters (like NOAAs Atlantic discussion), this can be very valuable in understanding the decisions made by the forecaster. This is also a big plus of using a pro weather router...you can talk to the forecaster and get a better understanding of the reasoning of, and confidence in, the forecast.

Some areas are notoriously hard to predict too, like the corner between Colombia and Panama. I was frustrated with trying to understand that area and discussed it with a pro. Even he said he would not forecast a window in that area more than 24 hours in advance or of more than 24 hours in duration. Just too unstable.

[barnakiel]

For the Med specifically (as well for any other landlocked sea), the subject gets an interesting twist: open sea (ocean) models do not work well over such small patches of water, neither do land models reflect what is going on over a lake this big ...

In the Med, other than discussing huge and well developed systems that will just wipe the whole area nearly irrespectively of the land/water boundary, the sailing weather will be dictated by the land/sea breezes. And our ability to sail well there will be vastly dependent on understanding when the breeze conditions appear and how these are going to create, or influence, the air flow.

So to say, we are imagining two flows: the overall pattern resulting from the highs, lows and fronts; and the breeze pattern resulting from the daily airflow patter over the sea/land boundary. And the two can either add up or cancel out too. To a various degree.

So, IMHO, in the Med, the Baltic, and other landlocked seas, the ideal would be to know the general pattern very well (highs, lows, FRONTS and their expected development) and when these are indifferent and stagnant, on sunny days expect plenty of breeze factor. And if the overall wx patterns are marked and vibrant, expect little breeze effect EXCEPT when the two flows add up. Then sail accordingly (and reef accordingly).

So, to wrap it up: have a boat and skills that sell very well in light winds (if you are a sailing kind of cruiser), motor otherwise. Nothing beat Air France upwind in stiff breeze ;-)

b.

[barnakiel]

Another side dish that I think is worth mentioning: nearly complete lack of local forecasting models in the Med.

As far as I know only the French have anything that resembles a proper met office and universities where people study and develop data harvesting, modelling and forecasting.

We can call it Uncle Sam met effect: sailors tend to forget that the whole N Atlantic is very very well covered by the US taxpayer paid agencies. Step into the Med ... and look at the sky somewhat more often than one might at that wx forecast graph ...

b.

[vlathom]

We sail the Chesapeake Bay..for 40+ years. In addition to the marine weather reports, I check the nearby buoys for current conditions. Recently, we had 1 ft. waves and 5 mph winds from a buoy. We asked a boat coming into the marina what it was like. He said, 4 to 5 ft waves and 20 to 30 mph. I guess buoys are too low to get an accurate reading.

[deblen]

Originally Posted by vlathom

We sail the Chesapeake Bay..for 40+ years. In addition to the marine weather reports, I check the nearby buoys for current conditions. Recently, we had 1 ft. waves and 5 mph winds from a buoy. We asked a boat coming into the marina what it was like. He said, 4 to 5 ft waves and 20 to 30 mph. I guess buoys are too low to get an accurate reading.

You may also be experiencing effects from nearby land,as Dockhead mentioned. Moving a short distance on a partially enclosed body of water,you can go from calm to windy in a few miles. Amost impossible to forecast,because it is not due to a storm,which can be seen coming 1000 mi. away.
/ Len

[fuentes]

I pay attention to and follow hurricane forecasts. The weather people follow them and inform for days. They are worth following! Even if they are hundreds of miles away from you, try and keep track on how it can affect where you are at and where you are headed. Keep in mind if there is somewhere to hide and if you have the time to get there. As a previous poster stated some time back. The shore is where the rocks are. If you are in a protected area, I would not argue and stay put.




As far as the 5-10 day predictions in my area (Sea of Cortez), I take them as a reference not an absolute. Kind of like the marines. Prepare for the worst and hope for the best. Keep a constant vigil for "chubascos"! They can come on very fast. So I believe in proper watch at all times (day and night) while under way. Half way relax in (protected?) area. The winds are constantly changing in speed and direction. Not necessarily what windfinder says. I figure this is sailing. Otherwise I would get a motor boat. I guess that is what makes El Caribe such a nice place to sail during the season! Have a nice day.

[vlathom]

Deblen:
We had the same experience with buoys off shore before crossing from Florida to the Bahamas. Over three years, we found the buoys almost useless. Reads calm and we go out and meet up with 7 foot waves. What is it with buoys?

[Prairie Chicken]

We sail in the Balearics--islands in the Med. After decades in the area I still can't figure out that island wx, but undoubtedly the sea/land breezes are a large factor.

We faithfully check at least two forecasts each day before setting off. (It's the pilot in me; I just can't help myself.) We are routinely amazed by the variation of two or more forecasts, and their lack of accuracy. We do not put much faith in the forecasts. Currently we're using El Tiempo & Windguru.

Having said that, since the advent of internet weather, I don't think we've been caught out once in a gale whereas it used to occur at least once a month if not more often. Access to the met websites allows us to see the 'situation'--highs, lows, what's coming, what's passing, where, when. From that perspective, we've found it extremely useful.

[Kenomac]

Originally Posted by meirriba

The gribs around Messina show ~20kn. What area you have referred to with ~2.2kn?

As to reliability you must take everyhing as probabilities. I keep on file a forecast received mid-Atlantic during ARC2003. It warned of a 'major tropical event, gusts over 80kn'.
The actual wind was 15-20kn.

Please look at the bulls eye in the pocketgrib screen shot. That's where we were when The video was recorded of us in 2-3.5 meter waves and 24-38 knot wind when the forecast called for 2.2 knots as seen in the screenshot. Messina was a day earlier when we were hit by 55 knot wind.

https://m.youtube.com/watch?v=s0HgonCDFxI

[Sulaire]

Ken,

Try predictwind, they show the "jets" that come off the foot of italy very clearly, we have found pw useful as it takes into account land masses, you need to subscribe to get the best out of it, but it is worth it. Throw in a bit of windguru and turkish university forecast gribs and you will have 3 or 4 models to look at, but pw is our go to and has been for many years.

[barnakiel]

Yes. That Venezuela/Colombia hook is similar to wx situation RSA coast Port Elisabeth to Richards Bay: small nasty coastal Low cell often not visible on analysis chart. In RSA the extra factor is that the Low not just pops up but also travels down the coast.

The good news is we know they CAN be there and so we will sail as if we expected one at any given time (=conservative estimates, fast sailing, one eye on the baro the other on the skye).

b.

[Sulaire]

When cruising under the foot of italy, it pays to pay attention to the winds on the top side of the foot,any medium stregnth northerlys there get accelerated through the mountains into jets like this for this coming monday, again pw shows this up well.

[Kenomac]

Thanks Charlie. Predictwind looks and works like a close up version of Weather4DPro. It provides more detailed information. Another arrow in our quiver.

The more I mess with the Predictwind app, the more I like it. It's earned it's way onto the front page of the Ipads and Iphone.

The best thing..... It's free!

[gulfbreez]

In Florida we would get forecast (on TV) that said 2-3 foot seas, I swear when we got around the corner of Sarasota Bigpass it was 6 footers. Typical. That was back in the good ol 90s though and before the Internet went big.