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Old 22-07-2011, 21:45   #1
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Weather Odd in Caribbean

Quote:
AN ACTIVE TROPICAL WAVE IS APPROACHING THE WINDWARD ISLANDS
ALONG 18N55W TO 11N57W MOVING W TO WNW NEAR 15 KT. SATELLITE
IMAGERY INDICATES BROAD CYCLONIC FLOW IS AROUND THE WAVE AXIS.
TOTAL PRECIPITABLE WATER IMAGERY ALSO SHOWS A SURGE OF DEEP
LAYER MOISTURE IS MAINLY W OF THE AXIS. SCATTERED
MODERATE/STRONG CONVECTION IS FROM 12N-15N BETWEEN 56W-61W
Hmmm.

Seems to be heading south west which is a bit weird.
Last 3 sat pics showing the bottom section developing south towards Tobago.

Hope it passes over before developing.

The current tracks all show it heading WNW... weird.

Would be happy with some thoughts from those watching Caribbean weather.


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Old 22-07-2011, 22:21   #2
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Re: Weather odd in Caribbean

Tropical waves crossing the Atlantic at this time of year is quite normal. Look at the various wind/wave charts at Noaa - Radiofax Charts - New Orleans
- - Pay particular attention the the ITCZ as it snakes up and down across the Atlantic. Currently the western end is above Trinidad which keeps the Tropical waves away from there. For the next 3 months, Grenada will get Tropical waves at about 4 t 7 day intervals. As the summer progresses you will notice the Tropical Waves turning into Tropical Storms as soon as they cross over the Windward Islands. As the summer progresses into August and especially Sept/Oct you will see the Tropical wave "spin up" into Tropical Storms while still east of the Windwards. These need to be watched carefully.
- - Down below the NOAA wind/wave charts is the Surface Charts section. Look at the "Surface analysis (E half)" for what is actually out there at the time of the chart. The actual position of the ITCZ versus the forecast position in the wind/wave charts will tell you a lot about what can get to you. You will notice that the Tropical Waves start out real low around N10 degrees but as the wave moves west it shifts north and you end up at the lower tail end in Grenada. A little extra wind for the wind generator and rain but not much else. The last 3 years there were rather boring. My favorite kind of weather boring.
- - If you know how to read pressure charts you can get the 17 day forecast based on the GFS model from: Maps : Weather Underground
- - You need to click on "animate" to get the individual days to load and then loop. The probability of actual formations is rather low on these charts as you go beyond 4 or 5 days. But they will give you a feel for the trend for the next two weeks or so.
- - Satellite photos from: NWS Southern Region - Central Atlantic Infrared Loop
will give you the current and recent past of what's out there. You can turn on the Lat/Lon grid to see how it matches with the NOAA Wind/Wave charts. You can turn on SST and see the sea surface temperatures across the Atlantic. Historically you need about 30 deg to get storms going in mid-Atlantic. You can turn on the HDW-high and see the wind arrows of where the storm system is heading.
- - You can call up the Sahara Dust charts at: Saharan Air Layer (SAL) - Split Window - Combo - Latest Available
They will show which parts of the Atlantic are being shielded by airborne Sahara dust. If the dust (red and yellow) stays south towards the equator there are few if any Tropical Storms. If the dust clouds move north and uncover the Tropical Atlantic waters, the waters can heat up and spawn some nasty storms.
- - For the last 3 years the dust has been staying south and we got little of anything in the Grenada region. What did spin up curved north and went towards the mid-north Atlantic before it got to the Windwards.
- - Don't get too hyper about what you read and hear on "government wx" reports. They tend to be over-inflated towards doom and disaster. Look at the real charts yourself and the satellite loops and you can see what is developing and where it is going.
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Old 22-07-2011, 22:36   #3
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Re: Weather odd in Caribbean

osirissail, that was an extremely tasty meal. And my simple ir and water vapor animated satellite guess was much the same on current conditions. But your views on picking future ripening canes was instructive.
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Old 23-07-2011, 05:11   #4
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Re: Weather Odd in Caribbean

Mark,

The wave you looking at is the one that NHS thinks may develop into something interesting once it reaches the Bahamas. The part you saw heading SW is simply the counterclockwise rotation that began developing a couple of days ago as it moved westward. This link shows the development MIMIC-TPW. As Osirissail mentioned, this is the normal state of affairs in the Caribbean during the summer.

BTW, looks like another one beginning to spin east of the Cape Verdes.
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Old 23-07-2011, 06:27   #5
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Re: Weather Odd in Caribbean

Quote:
Don't get too hyper about what you read and hear on "government wx" reports. They tend to be over-inflated towards doom and disaster. Look at the real charts yourself and the satellite loops and you can see what is developing and where it is going.
And on the other side of the coin, don't get too hyped up by all the yacking by amateur meteorologists predicting what is going to happen ten days or two weeks out. I personally think the national hurricane center stuff gets better and better each year, particularly when it is far away from US landfall. In other words, what they are saying and showing for the Caribbean is pretty good. But as US landfall gets imminent they start hedging and fudging and they try not to be too precise, to the point that you can't really hear the actual position and track on NOAA Weather Radio once the storm is within a day or so of your position. They just keep repeating warnings to evacuate, etc. But, the Internet stuff from the NHC remains quite good right up to landfall.
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Old 23-07-2011, 06:47   #6
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Re: Weather Odd in Caribbean

And don't forget the simple rule of 3, 3 days out 300 miles of variation posible, 2 days out 200, and a day out 100.
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Old 23-07-2011, 06:55   #7
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Re: Weather Odd in Caribbean

Cruising is fine when sailing in the right season. I can surely tell this is no longer the right season.
In the last month theres been more and different Cirrus cloud; cumulus convection making trade winds clouds shoot straight up, a number of days with disparate clouds at all levels, squalls that seem a little more variable in direction and course and with more variable wind speeds.
Its all much more 'interesting'. And one wonders if September will be too interesting!

Quote:
As the summer progresses you will notice the Tropical Waves turning into Tropical Storms as soon as they cross over the Windward Islands. As the summer progresses into August and especially Sept/Oct you will see the Tropical wave "spin up" into Tropical Storms while still east of the Windwards. These need to be watched carefully


I've noticed some of the archive tracks show a upgrade in Category when the cross the islands and had wondered if it was an illusion or not. Thanks for the confirmation.
Spinning up to the east of the WI is the tricky bit because we get less warning than others. However, they should also be of less intensity here...

Thanks for everyones thoughts and links.

Mark
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Old 23-07-2011, 07:10   #8
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Re: Weather Odd in Caribbean

In practice, virtually nobody can tell where a Tropical Storm/Named Storm is exactly going outside of 2 days or about 48 hours (+/-). If you look at the Probable Path projections of the NHC/NWS for more than 48 hours you will see a cone of probability that widens to over 500nm. Which means in the eastern Caribbean the storms could hit anywhere from Grenada to Antigua. But when you get down to 48 hours and less the the cone of probable path tightens to a couple hundred miles. What with big storms being a hundred miles wide, you now have a reasonably good idea if you are "in play" to get some nasty stuff.
- - It takes about 12 to 14 hours to motor-sail to Trinidad from Grenada which is enough time to "get out of Dodge" if the storm is likely to cross over the area. I was in Grenada for Hurricane Ivan and would never stay there if threatened with that situation again. So thereafter during August to November, I kept my boat ready to move/depart in a hour or less. One year we got down to 42 hours before the storm hooked a right turn and went north. But we had already packed everything away and got the lines shortened down.
- - I use the word "motor-sail" as within 48 hours or less the huge effects of the low pressure system will negate the trade winds and actually cause winds to come from the west. The old folklore in the eastern islands is that if the winds die to nothing or reverse it is time to head for the high ground, something big is coming.
- - Basically, there is only one raw source (not counting the French for the French Islands) of weather data in this hemispheric area and it is the NWS/NOAA and their satellites. You can and do have internet access to all the basic data in chart and photo versions and can use them to either agree with the NWS/NHC forecasts or disagree.
- - Having been in the meteorology business for over 55 years I can heartily recommend Steve Dashew's "Mariners Weather Handbook." It is quite thick, and if you can successfully get through it you will have a very good knowledge base on weather as it can affect cruising. See: SetSail Blog Archive Mariners Weather Handbook: A Guide to Forecasting & Tactics I have it on CDrom as the actual book is very thick and heavy.
- - The guys back in Miami sitting in a concrete building with no windows really don't have the level of vested interest you have sitting on your boat bobbing in the bays of the eastern Caribbean. Any and all sources of weather information are valuable in helping you to visualize and decide what to do. So, IMHO, learning how to read and interpret the weather charts and photos puts you in "command" of your future and the safety of your boat and crew. Which is what long term cruising is all about.
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Old 23-07-2011, 07:42   #9
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Re: Weather Odd in Caribbean

Quote:
Originally Posted by osirissail View Post
The old folklore in the eastern islands is that if the winds die to nothing or reverse it is time to head for the high ground, something big is coming..
That happened yesterday evening. Wind went into the north and then north west.

Yes, tanks full, ready to go, courses plotted etc.

Quote:
the level of vested interest you have sitting on your boat bobbing in the bays of the eastern Caribbean. Any and all sources of weather information are valuable in helping you to visualize and decide what to do. So, IMHO, learning how to read and interpret the weather charts and photos
Yep. Certainly good for learning the weather of an area.

I much prefer the idea of being here than further north. Those people have much further to head south if they try to run, and have a higher change of being in the dangerous quadrant if they make a mistake.
Here, I would be very unlucky to get onto the dangerous quadrant in a run to Trinidad or V.


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Old 23-07-2011, 12:05   #10
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Re: Weather Odd in Caribbean

This wave's the strongest one we've had so far this season, at least up here in the Leewards. I managed to get a quick round of golf in this morning before the heavens split open about noontime. Then came the lightning, gusty winds up to 40 kts, and lots of rain, about an inch per hour for the last three hours. The good news is that my cistern is overflowing!
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Old 25-07-2011, 10:44   #11
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Re: Weather Odd in Caribbean

Since we all can't have Osirissail along, the next best thing is to sign up for NOAA's storm/hurricane emails. They update every six hours when there is a storm around, they carefully tracked Cindy who was born and died in the oblivion of the North Atlantic last week. Whch brings us back to Mark's first post, the weather is odd, how can a tropical storm form in the North Atlantic where the water is much cooler?
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Old 25-07-2011, 17:17   #12
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Re: Weather Odd in Caribbean

Quote:
Originally Posted by Hannah on 'Rita T' View Post
. . . Which brings us back to Mark's first post, the weather is odd, how can a tropical storm form in the North Atlantic where the water is much cooler?
Answer: Because the government meteorologists are increasingly illiterate like most of the population. Cindy should have been called an "Extra-tropical Storm" which is the same thing but formed above the Tropics. Tropical storms form in the "Tropics which is a region of the Earth surrounding the Equator. It is limited in latitude by the Tropic of Cancer in the northern hemisphere at approximately 23 26′ 16″ (or 23.4378) N and the Tropic of Capricorn in the southern hemisphere at 23 26′ 16″ (or 23.4378) S.
- - If the "Extra-tropical Storm" forms and tracks just offshore of New England it would be termed a "Nor'easter." because the primary wind on land would from the northeast.
- - Like most folks including myself, laziness is a major impediment to being properly understood. Lazy language when combined with not understanding the complexities of a language are increasingly changing the language. For instance, there are no "Lobsters" in the Caribbean. The have always been and been referred to as "Langosta" which is a regional name for the "clawless" version. The Clawed version found in the northeastern regions of the North America are properly called "Lobsters. But now you will see, read and hear the restaurants and markets in the Caribbean adopting the name "lobster" rather than "Langosta."
- - Same with cyclonic storms with winds above 64 knots. In the Tropical Atlantic they are called "Hurricanes," while in the rest of the world they would be "Typhoons."
- - Also maybe it is just the result of the increasing "globalization" where people from all over the planet have access through the internet to all the meteorology data and would rather have only one term/name for the same weather condition anywhere in the world rather than having many "regional specific" names.
- - Cyclonic storms do not need "hot" water to form, they form in the winter as well as the summer months. Upper air eddies from the jetstreams can start a low pressure area rotating and you end up with a cyclone/extra-tropical storm/Tropical Storm/etc.
- - For the Caribbean, if you access the satellite photos at: http://www.srh.noaa.gov/srh/tropical...l_ir4_loop.php and click on "HDW-high" you can see the if there is any rotation in the upper air systems which will convert a tropical wave into a tropical storm.
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Old 29-07-2011, 06:57   #13
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Re: Weather Odd in Caribbean

Well theres a wave turning odd and anti-clockwise.

Its very low down at 8N 39W

Its heading due west at the moment. NHC says W to WNW at 30% chance of development in 48hrs.

Passage weather shows a track to hit BVIs.

Certainly its south enough to be a very southerly track if it goes the wnw route.


Thoughts from the weather guru's?


Mark
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Old 29-07-2011, 07:04   #14
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Re: Weather Odd in Caribbean

I note Wind Guru has an interesting week for Puerto Rico.

But I spose they are using the same model as Passage Weather.

Fine for me if it goes that far north, but its very early days yet.
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Old 29-07-2011, 08:47   #15
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Re: Weather Odd in Caribbean

To make weather forcasting more confusing, there can be 8 different computer models of a weather pattern. Programed by 8 different groups many from different countries. Nobody can guess where a jetstream will be greater than 24 hours in advance.

The most accurate forcast is "what you see is what you get".
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