Archive | March 2013

Diary of 1949 Typhoon Allyn: Part 2 – Conditions worsen

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

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.

Page from Consolidated Report on 1949 Typhoon Allyn

Page from Consolidated Report on 1949 Typhoon Allyn

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.

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Diary of 1949 Typhoon Allyn: Part 1 – Preparing for the storm

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.

1949 Typhoon Allyn's path through the Pacific

1949 Typhoon Allyn’s path through the Pacific

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.

A tale of two storms

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.

1989 Typhoon Gay

Time series of the winds associated with Typhoon Gay

Time series of the winds associated with Typhoon Gay

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.

Typhoon Gay during development

Typhoon Gay during development

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.

2005 Hurricane Dennis

Hurricane Dennis in the Caribbean

Hurricane Dennis in the Caribbean

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.

A first hand account of a typhoon landfall from 1949

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.

Damage from 1949 Typhoon Allyn

Damage from 1949 Typhoon Allyn

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…

How do I classify this? False eyes

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.

Odette (1985)

Odette (1985) 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.

Ami (2003)

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.

Ami_2003_falseeye

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.

Keith (1997)

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.

Keith (1997)

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