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Old 02-10-2009, 09:10   #16
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Originally Posted by barnakiel View Post
No - I mean the white squall - anybody first hand experience?

I talked to a skipper of a boat hit by a waterspout, but have never met anybody who been thru the famous, and according to some sources - quite common, white squall / microburst.

Anybody?

b.
See above- it was clear air at sea level so I'd call it a microburst. Does that count?
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Old 02-10-2009, 09:46   #17
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Is there any research / info available on microburst-related things over open water (as opposed to over the landmass)?

Do the microbursts happen over the oceans? Or do they need a landmass to form?

It may be a naive question - but PLS observe - tropical cyclones do NOT form over landmasses. Thus, it may be, that microbursts do NOT form over oceans ... (???)

Any data from USCG? Insurance compaties?

I have not seen any other reference to the white squall (possibly from a microburst) than in the movie.

Perhaps Gord?

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Old 02-10-2009, 10:31   #18
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That's what I love about radar, I avoid them all, black or white, waterspouts too!
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Old 02-10-2009, 10:34   #19
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From
Pride of Baltimore - Wikipedia, the free encyclopedia

On May 14, 1986, returning from Britain on the trade route to the Caribbean, what the US Coast Guard later described as a microburst squall, possibly a white squall, 250 nautical miles (463 km) north of Puerto Rico struck the Pride. Winds of 80 knots (150 km/h; 92 mph) hit the vessel, capsizing and sinking her. Her captain and three crew were lost; the remaining eight crewmembers floated in a partially-inflated life-raft for four days and seven hours with little food or water until the Norwegian tanker Toro came upon them and rescued them.
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Old 02-10-2009, 10:38   #20
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Originally Posted by Cheechako View Post
That's what I love about radar, I avoid them all, black or white, waterspouts too!
I kinda doubt it would show up on radar ( there was not much entrained water)- and it was quick.
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Old 02-10-2009, 10:50   #21
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... Do the microbursts happen over the oceans? Or do they need a landmass to form?...
I don't know.

A downburst is a strong downdraft which includes an outburst of potentially damaging winds on or near the ground.

If the diameter of the downburst is less than 2.2 miles (4 km), it is called a microburst (by definition).

A microburst produces straight-line winds, which can be greater than 104 mph (167 kph), and as much as 168 mph (270 kph)

Studies have shown that they predominantly occur in the High Plains and western U.S.: particularly in unstable, very dry low level environments with surface temperature-dew point spreads of 30 to 50 degrees and an area of mid-level moisture as a source for the weak showers.

There are other, less studied, types of micrbursts, some of which may occur over water.

Microburst Handbook
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Old 02-10-2009, 10:53   #22
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On land, they're reported here in the Midwest every year or two.
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Old 02-10-2009, 11:05   #23
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Good point, maybe a micro burst wouldnt show up on radar. I know thundercells do and Water spouts do... I assume the thundercells show up from the cloud density and electrical activity as well as any water...?
Hmmm.... rethinking...I guess a microburst would show up because of what it causes on the surface of the water right?
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Old 02-10-2009, 11:15   #24
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barometric change??
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Old 02-10-2009, 12:18   #25
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Good point, maybe a micro burst wouldnt show up on radar. I know thundercells do and Water spouts do... I assume the thundercells show up from the cloud density and electrical activity as well as any water...?
Hmmm.... rethinking...I guess a microburst would show up because of what it causes on the surface of the water right?
Dunno- for us the wind came first then just surface spray. No significant waves. I really don't think there'd be a lot of time to react, but FWIW we didn't have the radar on. The clouds bottoms were pretty high though and no lightning.
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Old 02-10-2009, 12:40   #26
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What we called a micro burst.

Five or six years ago on the Weeki Wachee river. We had just pulled up to the dock in the jon boat. Aboard were grandma and grandpa, mom and dad, and the two sons. It had rained on and off for a couple of hours - nothing new in Florida in the summer time with thunderstorms that normally provide 20-40 knot winds as they hit. Wind started picking up so grandma and grandpa and wife were told to hop out first and head for the house. Off they went. Sent the the boys next as I tied the bow. Wind picked up a lot - wow, I thought, that is high. First three at the house with the door open, boys in mid yard, me on dock. Wind went WAY HIGH. The door to the house could not be closed (I took a second to wave a warning to the wife). The boys went to ground and I jumped back into the jon and hunched down on the bottom. 15 seconds later only mild breeze. We were all stunned at the ferocity of it, looking at each other like "What the heck was that". All OK. Some limbs down. All items in back yards of the houses as far up river as I could see had moved. Some items between houses were to the street or over it. Weird. Scary.

So that was it for me/us.
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Old 02-10-2009, 12:41   #27
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... maybe a micro burst wouldnt show up on radar. I know thundercells do and Water spouts do... I assume the thundercells show up from the cloud density and electrical activity as well as any water...?
Hmmm.... rethinking...I guess a microburst would show up because of what it causes on the surface of the water right?
Yes, automatic detection of microbursts with Doppler radar data is possible.
Traditionally, manual detection is performed by meteorologists who scan through the volumetric radar data for appropriate signatures, bringing to bear human powers of pattern detection and analysis. More recently, automatic systems have been devised to perform this detection using computer techniques together with fuzzy logic.
Still, I THINK (?) Airport wind shear warnings are mostly issued based upon the observation of precursor conditions.
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Old 02-10-2009, 12:57   #28
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I was crossing Lake Livingston in Texas in a Starwind22 and watched a thunderstorm start down the lake.

The thunder had been getting more and more ominous and I was trying to make it back to the marina but was about a half mile short when I got hit.

I had already tied down all the sails, closed up the hatches and put on my big offshore type lifejacket as soon as things started looking bad.

I was looking down the lake toward the damn and watched as that entire area just disappeared into a white mist.

The wind was now blowing so hard the waves were going flat. Just before the bulk of the white cloud hit me I turned the boat into the wind and firewalled the throttle.

An 8hp Evinrude is not the best power source when you want to get anywhere in a hurry.

The rain had the finest drops I've ever experienced. It was like being in a really big garden sprinkler all of it pointed at your face.

I was trying to keep the boat pointed into the wind but was slowly starting to fall off to starboard and when I pushed the tiller to get back on course the boat fell off more. It was at that point I realized we were going backwards with the engine going full throttle into the wind. I put the tiller hard over to port and let her come around to run with the wind.

She came round like a shot, almost on her beam ends but quickly stood back up and ran before the wind for a few more minutes until the wind slacked off to about 25kts.

I could once again see where the marina entrance was and I beat feet for cover. The lightening was now coming thick and fast and all I wanted to do was get off the boat and away from the mast.

I flew into the marina and into my slip like a racecar coming to the pits. I jumped off, threw a single dockline on a cleat and beat it to the marina store for cover.

The little blast lasted less than 15minutes but was one of the more scarey times I've had on a boat.

The anemometer at the dam clocked a 72mph flat line wind. I can"t say for sure how strong the wind were I was but I've never seen waves blown flat before and the ultra fine rain was as strange as it gets.

A lake version of a white squall maybe?..............m
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Old 02-10-2009, 13:15   #29
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Yes, automatic detection of microbursts with Doppler radar data is possible.
Traditionally, manual detection is performed by meteorologists who scan through the volumetric radar data for appropriate signatures, bringing to bear human powers of pattern detection and analysis. More recently, automatic systems have been devised to perform this detection using computer techniques together with fuzzy logic.
Still, I THINK (?) Airport wind shear warnings are mostly issued based upon the observation of precursor conditions.
Cool, but i don't know how much that's help us out on the water.
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Old 02-10-2009, 13:20   #30
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The rain had the finest drops I've ever experienced. It was like being in a really big garden sprinkler all of it pointed at your face.
Didn't have that, just surface spray (felt like I was being pelted by BB's but it may have been part rain, who knows- I was otherwise occupied and didn't look up)

Pretty interesting- was it rain or surface water for you?
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