2004-09-03 FCST: Ivan (Atlantic)

[David Wolfson]

The satellite looks spot-on. Maybe the Navy has a satellite they're not telling NOAA about? :?

 

[Patrick Kerrin]

Originally posted by Jeff Snyder
... GOES 10 satellite, which, per the chart on http://www.ssd.noaa.gov/PS/SATS/goes-eclipse.html , eclipses currently from 0800z-0950z and then from 1020-1030z. The satellite perspective of the Carribean from GOES10, however, is very \"angled\".

It is quite an angle ATTM. See the CSU GOES 10 IR full disk (currently also 0600 UTC):

http://www.cira.colostate.edu/Special/Curr...x/G10full40.asp

I am just guessing, but the NRL Monterey Marine Meteorology Division may have an effective perspective shifting algorithm that they use to provide the nice "overhead" view in question.

 

[David Wolfson]

They're just starting to catch it on Grand Cayman. The first big squall of the main circulation is hitting and they had over an inch of rain in a few minutes. Steady winds nearing forty gusting to seventy, baro starting to drop fast.

 

[MClarkson]

total rainfall allready up to 10 inches at http://www.weatherincayman.com/

looks like ~2 inches over the last 20 minutes.

 

[MClarkson]

another 2 inches in the last 10 minutes

"Rain Rate: 15.16 in/hr "

 

[Steven Williams]

Thats a ridiculous rain rate. Will it be accurate. :shock:

 

[MClarkson]

http://www.weatherincayman.com/

seems to be down now

 

[Thomas Loades]

The Caymans are definitely in the thick of it now — the eye is south of Grand Cayman (or what I assume is Grand Cayman), and probably won't passs over the islands, so they've got a couple of hours of eyewall to look forward to.

 

[Tim Vasquez]

These graphs from Caymans are quite interesting... looks like anemometer broke at 90 mph:
http://www.weatherincayman.com/currcndx.htm

Tim

 

[David Schuttler]

I like this chart as it looks like after it broke it took a little while to quit spinning

http://www.weatherincayman.com/zf1ej/vws1325.jpg

 

[Glen Romine]

Originally posted by Tim Vasquez
These graphs from Caymans are quite interesting... looks like anemometer broke at 90 mph:
http://www.weatherincayman.com/currcndx.htm

Tim

If you look at the time stamps on everything, all of the data stopped at 8:10 am, which coincides with when the extrema occurred. Also, interesting that the wind direction was northerly early, then shifted around to the south west for the max at the end of the data record - suggesting the peak winds recorded were on the southeast quadrant of the hurricane, yet the island is actually in the northeast quadrant - so I'm not sure about any of these measurements when combined with the obviously faulty rain rates.

Glen

 

[David Schuttler]

Rain rates are off from wind blown rain ???

 

[Glen Romine]

Originally posted by David Schuttler
Rain rates are off from wind blown rain ???

I can't know for sure - but most rain guages are tipping bucket type. In that case, only water falling into the funnel will be counted - and rain rates are not changed by the horizontal wind (rain drops are moving horizontally with the wind, and fall at the usual speed). The wind shouldn't cause the bucket to tip assuming a reasonable instrument design. So, a few possible explanations: Rain accumulating on another surface (such as a roof top) is close enough to the rain guage to get blown into it. Or, if the rain guage is close to surface water (ocean, pool, flooded ground), water could be lifted up by the wind and considerable quantities of spray are being caught by the rain guage. Not the rain accumulation for today is 72 inches - which is six feet of rain. When you consider the size of the rain guage opening - that is a huge amount of water that would have entered the rain guage. More likely, the units are incorrect (mm/hr), or the instrument or software are not functioning properly.

Glen

 

[Austin Ivey]

I completely believe the rain rates reported by the station.

I own a vantage wireless pro and I've gotten a rainfall rate of 7.27in/hr here in new mexico during a monsoon storm in july. The rain collecter cups are very large and are shaped so as not to be skewed by wind blown rain. The rain falls into a 24 inch (tall) cup and then is measured in .01 inch increments by a scale like device that tips back and forth when it fills with .01 inch of rain.

Also remember that the 15in/hr reading could have only happened for 30 seconds or less...depending on how fast the scale was tipping back and forth. So if it would have kept raining at that rate...15 inches of rain could have been recorded in an hour. The real total was probably far less than that (for one hour).

I totally believe that 15in/hr is possible in the 6th strongest atlantic hurricane in recorded history.

Actually if you look at the scrolling "climatology bar" on that web page, it says the maximum rainfall rate for the month was 96in/hr. This I might have a hard time believing, but until you've actually seen a tropical rainfall in the tropics (not florida) you can't understand really how "hard" the rain comes down in those areas.....particuarly when enhanced by a major tropical system.

 

[Glen Romine]

Originally posted by Austin Ivey
I completely believe the rain rates reported by the station.

We don't nkow the sampling rate for the reported rain rates - but the world record 1 minute rainfall rate would equate to 108 inches per hour. So, the 98 in/hr would be close to world record status if true. Also, the rain total of just over 72 inches would be a new world record if verfied. It is an intense hurricane - but I just don't buy it.

Glen