Typhoon Allyn was one of the most destructive to pass Guam. Although the eye passes some distance to the South, damage was severe over most of the island. the following is the conclusion of a diary of events during the 10 hours of the storm’s passage over the island.
“1705K: The eye of the typhoon passed approximately 45 miles to the south of the station between 1615 and 1630K. Our pressure has risen two millibars now and should continue to rise as the storm moves on.
“1720K: An item of interest might be that when the air freight terminal went to pieces, there were several cars wrecked. One in particular, a Ford, is folded up just like an accordion and is one complete wreck. Several other cars are almost as bad. The front end of the terminal building here is beginning to sag and the operations sections has a large hole in it. Doesn’t look good if these winds continue as they are.
“1800K: Forecast diminishing winds and eye passage given to radio at 1715K to be relayed to [other bases]. Courier from Harmon arrived 1730K and was given forecast. Wind at this timeis definitely swinging to south presently southeast at 70 knots with gusts to 85 knots.
“1915K: Forecast given … that winds would be 30 knots by [midnight], present winds SE at 50 knots with gusts to 60 knots.
“2200K: The winds are slowly dying down, but still holding steady around 40 knots with gusts in the 50s. Our pressure is on the rise still and by 6 hours everything should be well under control. Light rain is continuing to fall with intermittent heavy showers.”
So in the time span from noon until 10 p.m., the conditions went from showers to dangerous winds back to rain showers. The result was catastrophic. Nearly $20 million (1949 dollars, about $200 million in 2012 dollars) was done to military installations. The economy of Guam was also severely impacted. Most – if not all – of several important crops were destroyed: breadfruits (100% lost), vegetables (90%), banana (75%) and so on.
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.
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.
- 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.
- 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.
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.
What is rawin? What is the hydrogen shack? What is Antrac? What is a T-6? Well, I’m learning as I transcribe this, too. I’ve provided links to other sites that provide more information, but some things are still a mystery to me. For instance, Antrac appears to be related to air traffic control (that is, what I’ve learned from web searching). But I could be wrong.
The following is an hour of notes from Typhoon Allyn.
“1437K: Just went outside to check on the T-6′s at the east end of the ramp. They are not in sight. Don’t know whether they have been moved or whether they are out of sight on the low end of the ramp. It is very difficult to stand erect in the open. Andersen AFB is estimating 85 knots. No buildings have blown down but trees are starting to go over. The pole for the Antrac antenna is swaying about six feet at the top. One pole has gone down at the Rawin shack. The banana trees have been uprooted. Rawin reports that the T-6′s were still on the ramp the last time they went by.
“1445K: The corrugated roof on the inflight kitchen quonset is starting to tear off. One section is gone completely and another is starting to rip off. Estimate that the Antrac pole will stay up another hour or hour and a half.
“1455K: Capt. Myers just returned from quarters area, he said that the large hangar doors just went through th PLM hangar as he came by. Heavy rain just began to fall and the visibility has been reduced to less than one eighth of a mile and the wind is now hanging at about ninety knots. The rain is in sheets and horizontal with the ramp. Debris is beginning to fly and the inflight kitchen is still holding its own. The wind tee is just about demolished.
“1510K: The station is being used as a fire control center for this area. The fire marshall has men stationed and is standing by himself for fires that are reprted into this station. The observer will not be able to take psychrometer readings much longer as it is impossible to stand against the wind.
“1515K: Numerous power lines have blown down, and island power is due to go off at anytime. We can’t get the emergency power unit to work.
“1520K: The lights just went out. No emergency power as yet, but repair crews on the way. Estimating the winds at 80 knots and the visibility at three eighths of a mile in torrential rains.
“1530: Pressure is dropping on an average of four millibars per hour and the tendency is still down. The bottom is really falling out of this. Sheet metal is now tearing off of the depot hangars and the Rawin shack is OK; however, the hydrogen shack is going. The doors have been blown off and it shouldn’t last much longer. Debris is traveling along the ramp at about twenty miles per hour.
If you missed it, read the introduction to this article.
Before we continue the narrative, one should have an understanding of the time conventions in these posts. The U.S. military uses time zones named by letter. The “Z” time zone is the same as the UTC, the Universal Time Coordinate, which is the time in …. Guam – in the Western Pacific – is in the “K” time zone. So times listed in the report as “K” refer to local time. For instance, 17:00K is 5 p.m. local time. To learn which letter your time zone corresponds to, visit this web page describing time zones. Keep in mind that the following spans a three hour period.
Page 4: “Running diary of approach of Typhoon Allyn:
“Arrived at Harmon at 1145K on the 17th and set up shop. Things proceeding normally with winds increasing slightly. The nine light indicator at this station won’t last too long from the indications. It is warbling loudly and the count of the flashes at this time is impossible.
“1315K: Wind has now picked up considerably and the reports from North indicate that they are abandoning the station as the radar tower is about to topple over. We are estimating the winds at this time and cross checking with the Navy. The wind at Harmon is now tearing the inflight kitchen apart. The pressure is falling ominously. We are taking readings every 15 minutes and estimating the wind every 5 min. Also, setting up to take readings with the sling psychrometer and trying to keep an accurate count of all the happenings as they occur.
“1322K: A piece of wiod just went down the ramp must have been a 6×6 and 10 feet long.
“1325K: The rawin tower is no longer visible. Winds must be in the vicinity of 70 knots [80 mph] at this time.
“1336K: [A] communication man just came in and said that JMP is going off the air. They are evacuating the station. We are now out of contact with the rest of the Pacific area.
“1355K: Winds are really beginning to blow now. It is whistling thru all the wires, and the poles next to the stations have quite a list to them. Estimating the winds at 60 knots at this time. Wind tee is hanging on by shreds. Communications are out as they have evacuated both the Weather Central and Guam Broadcast stations, so we are out of contact with everyone but Navy. Rain is coming down in sheets and visibility is getting bad. Visibility at 1/2 mile at this time.
“1420K: Low scud 200 feet [high covering] about eight tenths [of the sky] and [completely overcast] stratocumulus clouds just above, moving beter than 50 knots. Antenna pole at the edge of the building now has a 6 foot oscillation.
The mystical nature of tropical cyclones is that they even form at all. They begin as convective cells (what could be called large thunderstorms). What appears to be a disorganized grouping of storm cells, can organize, begin spinning and in no time, appear to be a fully organized system. Of course there are very technical descriptions as to how this occurs, but from satellite imagery, it can be amazing to watch. While some of the larger convective (colder) cells can appear to be a separate system, they often are actually part of the original circulation. Here are a couple examples recently brought up on the talk forum at talk.cyclonecenter.org, both of which had two significant landfalls.
This system was interesting in that it is a system that began in the Gulf of Thailand – considered the Pacific Ocean – then moved west into the Indian Ocean, eventually making landfall in India as – potentially – a very strong cyclone. Of course I must qualify that statement because of the differences in the best track data. The graph at right shows the best estimates of the storm’s intensity, in maximum sustained wind speed. The system gained strength near day 2, then crossed into the Bay of Bengal and regained strength. At landfall in India, it was likely between 70 and 150 knots, kind of a large range. Some of these differences in intensity are due to the data available to each agency. Another could be in the interpretati0n of the imagery.
A recent talk post from ibclc2 noted the features in Typhoon Gay during its development in the Gulf of Thailand. The organization of the system is beginning to take shape. The convective cell near B is close to a banding feature (if you were doing a detailed classification). But it is not, since the region between it and the central part of the system is not warm enough (it needs to be red or warmer, see the field guide for more information). The portion near A appears to be an embedded center. But upon further review, there appears a warm spot just north of the darkest blue colors. It could be the beginnings of an eye, but only time will tell … and it does. In the next few images, that small warm spot becomes an eye just prior to making landfall on the Kra Isthmus. So how would you classify it? Well it’s likely best left as an embedded center with no banding. While there is the hint of an eye, the primary characteristics of an eye (cold cloud surrounding a warm center in a circular fashion) aren’t complete yet.
An image of Dennis recently noted by bretarn showed a large system. Similar to Gay above, the satellite image showed a cold center (A) with a large cold band to the east. The convection near A is showing some circulation, so the center is somewhere below that cold cloud cover. So it is an embedded center. Like the Typhoon above, this is an image just prior to an eye emerging. The next question is what to do with B. It is definitely associated with the system, because it appears to be wrapping around the circulation center near A. The region between A and B is warm, with the warmest color being red. So for a detailed classification, this might be considered a banding feature.
In its own right, Dennis was a very severe system, making landfall in Cuba and in the Gulf on the Florida panhandle. However, its fast movement lessened the impact. It is also less memorable because its Gulf landfall was eclipsed by Hurricane Katrina later in the season. Nonetheless, the name was retired from the North Atlantic hurricane names after the season.
In today’s society of 24-hour news and reporting via satellite, it is not uncommon to have unending first hand coverage of a hurricane, tropical cyclone, or typhoon as it makes landfall. In 1949, however, such an account was quite rare. At NCDC (NOAA’s National Climatic Data Center) we have historical records produced by the Air Force during the period when they flew aircraft into typhoons in the western North Pacific. One such report is the “Consolidated Report” which they produced for each typhoon. This report often includes the analysis of current conditions and forecast maps. It contains summaries of reconnaissance flights, communications, meteorological condition summaries and often a damage report.
One typhoon from 1949 – Typhoon Allyn – passed quite close to Guam. The forecasters there included in their “Consolidated Report: Typhoon ‘Allyn’ November 14-24, 1949″ a rare addition: a running diary of the typhoon’s approach to Guam. Over the next few days, I’ll be reproducing the diary here for those interested in a first hand description of the landfall conditions. While this doesn’t contain video feeds, or interviews with local residents, it provides insight into the strength of these violent storms and those who had to work through such conditions. This reproduction of that report is dedicated to those who provided forecasts to our armed services and helped protect lives and property during those years of service at Guam and other forecast offices in the Pacific.
Page 4: “During the morning of 17 November, the wind strengthened to 30 knots [34 m.p.h.], and the dark sky and falling barometer gave sure indications of the advent of the storm. Arrangements had been made for Clark [another Air Force Base] to accept forecast responsibility. Also, Haneda had been instructed to perform the functions of the Typhoon Warning Center, for it appeared certain that Guam’s contact with the [outside world] was to be terminated abruptly and for an indefinite period. Acting on instructions to retain responsibility as long as possible, the Center almost overplayed its hand. The plan called for the Center to issue bulletin 13 [bulletins are their term for a warning] by 17:30Z. Clark was to issue bulletin 14; however 15 minutes before the bulletin 13 was ready for transmission, the communication station ceased operations. It was only by special arrangement that this final message was transmitted. By 04:00Z, 17 November, the surface wind was near 50 knots [57 m.p.h.] making the weather station an unhealthy place due to the proximity of a 40 foot radar tower; consequently, all personnel evacuated to typhoon shelters.
“Due to the fact that the weather station at Harmon Air Force Base was located in a typhoon proof structure, it was manned throughout the storm. The following remarks have been taken from a log kept by forecasters who operated that station, beginning 17 November at 11:45K (01:45Z).”
The remainder of this diary chronicles the ensuing 12 hours of the typhoon’s interaction with Guam.
To be continued…
One of the challenging aspects of determining the storm type in Cyclone Center is the inability to view a storm snapshot in context. While classifying a set of images, you do not know which storm you are viewing and how that storm had been evolving before those times shown to you. This can lead to images that can be misleading to classify – one such image is the “false eye” storm.
A false eye is a circular feature of warm cloud that at first glance appears to be a genuine tropical cyclone eye (the center of a powerful tropical cyclone). Since we cannot look at other times during the process to see if the feature persists, we must look for other clues to determine if the feature really is an eye or not. The primary thing to look for is the storm structure outside of the suspicious eye. Does the storm look well organized? Are there distinct and tightly wound spiral bands? Are cloud tops very cold or not so much? Consider the following examples, all examined and discussed in the Cyclone Center Talk feature.
The black circle indicates where an eye could possibly be analyzed. But look at the cloud patterns outside of the “eye” for confirmation. Here we see no organized spirals and no circular eyewall (the cold ring the typically surrounds the eye). The clouds are certainly very cold, which is sometimes an indication of strength; but the overall lack of organization leads me to conclude that the “eye” feature is actually just a gap in the cold clouds and not really an eye at all. I would probably classify this as a weak spiral band type pattern, but nothing more.
The second example is from a very complicated cloud pattern, typically seen in what meteorologists call the “monsoon trough” region. This is an area where the ocean waters are very warm and atmospheric winds tend to come together in the lower atmosphere, creating a situation that is quite favorable for thunderstorms and sometimes tropical cyclones.
The black circle again indicates a circular area of warm clouds that may be mistaken for an eye. What I immediately notice is that there are two distinct areas of thunderstorms, labeled “1″ and “2″. Area 1 is showing some signs of organization, shown by the black lines, which indicate a turning or spiraling of the clouds. Little organization is seen in area 2, which is essentially a large blob of thunderstorms at this point. The eye in the middle is actually just a gap in between the 2 systems – there is no organization in clouds around this area.
I classified area 1 as a spiral band pattern. The center of area 1 is probably very close to the circled area (follow the black lines in). Since we are only classifying one system at a time in Cyclone Center, I ignored area 2.
To contrast the two examples above, lets look at a real eye. Keith was a very strong tropical cyclone that exhibited a well pronounced eye feature.
At first glance we immediately notice the features of an eye pattern storm: distinct spiral band features, high degree of symmetry, and cold/circular clouds completely surrounding the eye. Although there are even better examples of eye storms, I would classify this image as a mid-level eye pattern. The storm intensity is probably in the Category 2 to Category 3 range on the Saffir-Simpson scale.
I hoped that this helps you to become a better Cyclone Center classifier. Look for more help articles like this on a more regular basis throughout the next few months.
- Chris Hennon is part of the Cyclone Center Science Team and Associate Professor of Atmospheric Sciences at the University of North Carolina at Asheville
Even though the 2012 Atlantic Hurricane season has passed, CycloneCenter is still up and running, and is making progress through not only classifications on the website, but also promoting awareness to the public as well.
Last week members of the CycloneCenter science team attended the meeting of the American Association for the Advancement of Science (AAAS) in Boston, Massachusetts. There we got to engage with members of the science community, as well as the media. As a result, CycloneCenter has appeared in many different articles on websites, including Discovery News, Seattle Times, and even the French Embassy! It’s great to see that the media is focusing on citizen science. Without you, our efforts would not be possible!
In addition, we have recently passed the 150,000 classification mark! We once again thank you for your participation, and want to remind you to keep on classifying!
While there are only some results to talk about, the CycloneCenter science team is still active in presenting at national conferences. Last month was the AGU annual meeting, and this month was the annual meeting of the American Meteorological Society. Dr. Ken Knapp of NCDC presented an overall view about the science of CycloneCenter to a nearly packed group of tropical meteorologists. There was a lot of interest in the subject, including some chatter on the official AMS twitter account. This is a great example of how powerful social media can be.