Guest Blogger Margie KieperThursday afternoon update:
Recon once again found no closed circulation in the tropical wave and associated disturbed weather in the eastern Caribbean. And Generalissimo Francisco Franco is still dead.
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Usagi has made landfall in southern Japan in Kyushu, apparently at tropical storm strength or possibly Category 1 hurricane, for those familiar with the US scale -- or as a Severe Tropical Storm or weak Typhoon as classified by Japan Meteorological Agency (JMA). JMA's hourly observations from the Kyushu area and just north, show a low pressure of 973.5 mbar, highest sustained (10-min) winds of around 50 kt, and considerable rainfall: Nobeoka recorded 46.5 mm in one hour, and 183 mm total. The coast of the Kyushu Prefecture, including Miyazaki, Aburatsu, and Nobeoka, experienced the eyewall winds on the northwest side. Cooler water contributed to the rapid weakening.
Usagi is a large storm and its effects are still being felt as it travels over the islands of Japan.
The last vis image from last night showed the eye covered in cirrus; however microwave imagery continued to depict a large eye, with very little remaining convective banding, at the time the northwestern eyewall was over the Pacific coast of Kyushu:
Here's a photo of the waves at the shore in Japan prior to Usagi's arrival, taken by Typhoon Hunter:
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There is still no sign of tropical development in satellite imagery of the much-publicized tropical wave in the eastern Caribbean. We will continue to report faithfully on this non-development, and hope to be reporting on the lack of development of this tropical wave throughout the 2007 season ("Breaking news just in...Generalissimo Francisco Franco is still dead"). However, to quote from the Atlantic TWO, "THE SYSTEM STILL HAS SOME POTENTIAL TO BECOME A TROPICAL DEPRESSION DURING THE NEXT DAY OR SO."
Recon is scheduled for both this area of disturbed weather and the one in the Gulf of Mexico. The Caribbean invest is being monitored by three AF Hurricane Hunters who deployed to St. Croix the day prior to the scheduled mission, but for the disturbance in the northeast GOM the Hurricane Hunters will not have to travel very far from their home base in Biloxi, MS.
For those wondering about the potential of the tropical wave following 99L, all tropical waves in the hurricane season have potential. The experts at NHC keep track of things like that, and they document this information in the TWO (Tropical Weather Outlook).
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I see there are many questions regarding recon. The readings taken at flight level, if about about 300 meters, can be taken as surface windspeeds. Yesterday winds were light and variable (mostly 1 kt to 20 kt) and there was a broad center area of low pressure (a trough). The key readings required for a closed surface circulation will be westerly winds on the SW leg
(winds coming from 240 to 300 degrees). My recommendation: don't bother reading the HDOBS because when the recon flight is completed, the results will be in today's afternoon Atlantic Tropical Weather Outlook.
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Regarding the bridge collapse in Minneapolis -- which I can see outside the office window of my 25-flight-plus downtown location -- weather was likely a factor.
In the 1970s the newest way to build bridges was to incorporate steel encased in concrete. Concrete provided the compressive strength and steel the tensile strength. There are many, many bridges built using this technology, from about 40 years ago, that are still in use today. However bridges that are built today are built of concrete with the tensile support provided external to the concrete, via cabling, beams etc.
The problem is that the two materials contract and expand differently due to changes in temperature, with the steel changing more than the concrete. Over time this would create small stress fractures in the concrete, near the steel, and then over a longer time period this leads to greater fatigue fractures. Eventually the concrete has a catastropic failure and falls apart, and the remaining steel, which does not have significant compressive strength, collapses. This bridge was designed as one long open steel truss spanning the Mississippi, and I expect that the analysis will find that there was a failure of one of the concrete supports. There was a video showing part of the bridge at failure, which showed that the south side of the truss failed suddenly -- the side off-camera -- and that the shock through the truss caused a secondary failure on the other side of the bridge, in the truss, dropping it about 10 feet, for a couple of seconds, before the entire truss collapsed straight down.
Minneapolis has been in a continuing heat wave this week, and it seems each summer is hotter than the norm here, when you used to be able to count summer days above 85 degrees on one hand. We also get temperature extremes on the cold side in the wintertime; minus fifteen is not unusual. It has been hot the last week, and yesterday the high was 93 degrees in the late afternoon, and still 89 degrees at 6pm. This high of 93, followed daily highs of 90, 93, 96, 89, 89, 89, 91, and 91. When the temperature is this high, the steel would have expanded. At the time of the bridge failure, road crews were jackhammering on the roadbed above the truss; this was noted by someone who was on the bridge and was lucky enough to survive. This likely transmitted vibrations into the truss. Harmonic vibrations -- the right ones -- can trigger structural failure in already-fatigued structures. It was likely a combination of factors that provided the "last straw" that led to failure of some key part of the structure, most likely a concrete support. However there is also the possibility that the initial failure was in a key section of the truss that was fatigued by the heat and vibrations, but once the first failure occurred, the shock through the structure would have immediately triggered other failures, leading to a cascade that brought the entire truss down, with shock waves also bringing down the bridge structures on either side.
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