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Old 20-02-2009, 16:44   #1
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Musical lows in the Pacific

This looks like a game of musical chairs, played by lows in the eastern pacific:

We start with two lows in 24 hours: image

Move up to 4 lows in the game at 48 hours:
image

And then back down to 3 lows at 96 hours:
image

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Old 20-02-2009, 19:15   #2
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those are the same lows...

...being drawn by three different forecasters. Note the names listed in the title box after "FCSTR." The 24-hour forecast was drawn by Rowland, the 48 by Collins, and the 96 by Shoenberg. It's not a matter of musical lows, just musical forecasters.
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Old 20-02-2009, 22:01   #3
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On our second trip to New Caledonia from Brisbane, Australia, we faced a similarly confusing situation.

There was a cyclone 200 miles north of New Caledonia, but it was poorly organzied. We were about 500 miles from New Caledonia to the southwest. We downloaded the Australian weather fax that said the storm was headed toward Australia. Next, we downloaded the New Zealand weather fax that said the storm was headed toward New Zealand. Within twelve hours, the New Zealand weather fax said the storm was heading back toward Australia.

It is frustrating to figure out our storm avoidance plan when the weather faxes sent the storm southwest, then southeast, and then southwest again. The problem was that in a poorly organized cyclone, it's hard to pick the center of the storm on the satellite photos and using all the tools available to meteorologists. Once a particular forcaster picks the center of the storm, the next forecaster may pick a different location for the storms center, and that creates the impression that the storm has moved in a different direction. What really happened was that the forcasters had different opinions about the location of the storms center, and there was very little movement of the cyclone over the twenty-four period when we were trying to figure out the best method of storm avoidance. Situations like these create a lot of confusion.

When I was in the Navy staitioned at Roosevelt Roads Naval Station in eastern Puerto Rico, we had lots of tropical storms and hurricanes pass by each summer. In one memorable storm, there was a hurricane going through the northern windard islands heading our way. Before it got to Roosevelt Roads, the hurricane downgraded in intensity, and the navy meteorologists lost track of the center because it was poorly organized. It actually went directly over our base. When it emerged on the north side of Puerto Rico, it quickly reformed into a hurricane. I remember talking to one of the weather men on base, and they told me that they lost track of the storm until it reformed to the northwest of us.

There are lots of no man's lands in big patches of ocean where there aren't many weather observations. In those no man's lands, there are black holes where nobody is fully committed to giving accurate weather forecasts. On the trip from New Zealand to Fiji and New Caledonia, storms can happen that aren't shown on the weather fax because New Zealand and Fiji don't spend resources predicting weather far from their shores.

The moral of the story for me was that I always got weather information from more than one source. After I get all the information, I put it together to come up with a coherent storm avoidance plan.
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Old 21-02-2009, 04:53   #4
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...The moral of the story for me was that I always got weather information from more than one source. After I get all the information, I put it together to come up with a coherent storm avoidance plan.
That's my motto, Dave! During hurricane season, I have maybe 30 websites that I keep up with.
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Old 21-02-2009, 08:09   #5
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There are lots of no man's lands in big patches of ocean where there aren't many weather observations.
Hasn't QuikSCAT changed this, though? We now have windspeed data for all the oceans that is accurate and extremely detailed, and this is used to feed the major weather forecast computers. Of course the computer models use a grid that is too large to properly locate or model these tight low-pressure systems, but aren't humans at least looking at the QuikSCAT data?

(Disclaimer: I'm just guessing about most of this.)
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Old 21-02-2009, 10:53   #6
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Hasn't QuikSCAT changed this, though? We now have windspeed data for all the oceans that is accurate and extremely detailed, and this is used to feed the major weather forecast computers. Of course the computer models use a grid that is too large to properly locate or model these tight low-pressure systems, but aren't humans at least looking at the QuikSCAT data?

(Disclaimer: I'm just guessing about most of this.)
I'm not expert on weather, but I did sail around the world looking at weather faxes, grib files, and whatever else I could get my hands on.

On my tradewind circumnavigation, I found that the weather faxes were the most helpful. At least they identified the major weather systems coming my way, and I could use my barometer and cloud patterns to tell when the highs, lows, fronts, and convergence zones were arriving in my area. Also, the weather faxes were readily available and frequently updated. I downloaded them several times a day in some instances.

We used grib files a great deal, and they showed wind strengths and directions, and often they were right on the money. Also, often they were wrong. They are not designed to deal with hurricane and cyclones, so they are not particularly helpful when you need them the most.

I saw many cruisers afflicted with GRIB PARALYSIS. This disorder meant that they would not start on passage until they had favorable grib files. Sometimes they waited in port for weeks before their interpretation of the gribs was "favorable", and they felt like they should leave.

By the time I completed my circumnavigation, I changed the name of the GRIB FILES to "GRIB FANTASIES". The reason I did that was because people were looking out a week ahead of time with their grib files, and then they sailed off to fantasy land because the grib files said that things would be good five days out. We found that grib files were fairly accurate for a maximum of three days into the future most of the time. Anything beyond that time frame was delusional thinking on board Exit Only. And if there were any major tropical storms or hurricanes in the area, we didn't place much confidence in the grib files because they are not designed to deal with extreme weather.

I have seen buoy weather, grib files, QuikSCAT, and many other sources of information. My favorite remains frequent weather faxes in combination with my barometer, swell size and swell direction so that I can tell what is coming my way.

When my grib files make sense, I use them, but I don't trust them to predict my future. When I am sailing offshore, what I want to know most of all is what the weather will be in one or two weeks. Grib files and QuikSCAT don't predict the distant future, and the future is what I want to know.

It required a lot of mental discipline on board Exit Only to not take a trip to fantasy land while looking at the grib files and other weather data. It required even more discipline to frequently download weather faxes, record barometric pressure, and then interpret all the data in a sensible manner. I actually had to turn on my brain and think about what was happening in my weather world.
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Old 21-02-2009, 12:49   #7
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Hi, Paul.

The availability of satellite data has added a lot to the picture, true enough. As you said, QuickScat is one good source of wind data for remote areas, and "surface cloud drift" using visible and IR imaging is another. They require analysis by trained meteorologists, and the manipulated output is available on sites like the University of Wisconsin's Cooperative Institute for Meteorological Satellite Studies (CMISS) These types of sources tend to be fairly large scale in scope, and so are good for analyzing macro weather goings-on. For the weather that you would see over a few days cruising in your boat, I agree with Dave that weather faxes and GRIB data are the most helpful, and are the easiest to obtain, since they can be downloaded directly to your laptop via SSB and Pactor modem no matter where you are. A lot of the more sophisticated stuff requires a broadband connection, which means finding an Internet cafe ashore.
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