Archive | April 2013

Is it an Eye?

Identifying eye hurricanes is a main focus for the Cyclone Center team, but it is presenting some challenges for our citizen scientists.  Storms with real eyes are being categorized very well, with 80% to 90% accuracy in storm type.  However, storms that do not have eyes but look like they might are proving more difficult.  Many things, like blurry images or dark blue or white clouded centers have been shown to cause these mistakes.

A bizarre example of an image on Cyclone Center that is very misleading is the storm CYC1981.  The small white circle in the very center of the storm that at first glance looks like an eye is actually the island Niue in the South Pacific.  The satellite image was taken as the hurricane passed over the island, and the white land boundary lines look like the eyewall.

1981047S18181.CYC1981.1981.02.17.0900.47.GOE-3.030.hursat-b1.v05

CYC1981

Unfortunately, with the size of the images on Cyclone Center, it is hard to determine if this storm has an eye, and since having an island in the middle of a storm image is a rare phenomenon, it would be easy to assume that it did.  This image of CYC1981 even stumped most of our science team, so don’t feel bad if it tricked you too.

So how can we tell if a storm is or is not an eye storm?

Many storms look very similar in size and shape to eye hurricanes, but they lack an actual eye.  There are a few things that you can look for, however, to determine for sure whether or not the image you are looking at is an image of an eye storm.

  1. Is the center of the storm surrounding the eye cold?  You can tell this by the color of the clouds—shades of red, orange, and grey signify warm clouds while blue and white areas represent cold clouds.
  2. Is the eye itself warm?  The eye should be made up of warm clouds, usually grey or pink colored.  White and grey clouds are not one and the same; white clouds are very cold and grey clouds are very warm.

If we applied these three steps to CYC1981, we would find that it does have cold clouds at the center, but there are no warm clouds around where the eye should be and the band of clouds around the storm is very weak.

For more information, visit another recent post: How do I classify this? False eyes.

This post was contributed by Brady Blackburn, an intern with the Cyclone Center team from Asheville High School in Asheville, NC.

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Diary of 1949 Typhoon Allyn: Part 3 – The center passes

If you missed it, read the introduction to this article and part 1 and part 2.

This is the strongest part of the storm. Part 4 will conclude the diary and summarize some information from the damage report.

“1605K: Now getting gusts to 100 m.p.h. Everything still holding fairly well. Visibility is less than one eighth of a mile and rain is falling at a rate of about 4 hundredths of an inch per hour. Emergency lights still not working. Believe the starter is out. Pressure still falling. The clouds still the same with a few breaks in the lower stratus with overcast solid above. Ceiling is now about 50 feet.

“1620K: Put in for a call to Clark field and was greeted by a call from Iwo Jima. They want to close down operations there but advised that they stay in operation for at least 24 hours in case of emergency at this station. Gave them the latest information on the storm and our condition. The wind is estimated at 90 knots now and the visibility is almost zero. The ceiling is estimated at 50 feet in precipitation.

“1632K: Corrugated roofing just started tearing off the roof of the terminal, it made a tremendous crash when the section tore off. All of the troops that are using the terminal as a typhoon shelter had looks of apprehension and I can’t say that I blame them. Indications are that the barometer is starting to level out. The crash of sheet metal on the terminal wasn’t the terminal roof apparently but the remains of the freight terminal on the east side of us. Capt. Highley said that it completely collapsed.Visibility has lifted from zero to 3/4 of a mile but the wind still has 110 knot gusts.

“1650K: Report just received from the Rawin crew, who had just left their hut, and they say that all the buildings are going and that sheet metal is flying thick through the air. Looks like the center has passed us as we had a 1 millibar rise in [pressure in] the last 15 minutes, although will wait for one more observation before we draw any definite conclusions. Winds still haven’t decreased although they are beginning to vear into the SE. Maybe its past us.”

Part 4 will contain the conclusion of this diary and a summary of the damage report.