Storm Australian Severe Weather Forum

Severe Weather Discussion => Tropical Cyclones, Typhoons and Hurricanes Worldwide => Topic started by: Mike on 04 February 2009, 06:54:35 AM

Title: Professor Greg Holland /Hurricanes
Post by: Mike on 04 February 2009, 06:54:35 AM
we were fortunate here in Darwin to have Prof Greg Holland from NOAA and AMOS (Australian Meteorological & Oceanographic Society) to give a presentation on his findings over the years titled “Intense tropical cyclones: A bellweather of climate shift and change”.  I did not actually know what bellwether was...but it's from Roman times when they would pick the lead sheep of a flock and attach a bell around its neck, the other sheep would naturally follow the lead sheep regardless and if they were lost all the shepherd had to do is listen for the bell and he would find the whole group!  The things you find out later in life....

Prof Holland was forecasting at the Darwin BoM when Tracy slammed us so he had some storied to tell!  His main focus was on the Atlantic areas - given his expertise there - and displayed graphs from early years to the present and how the trend in SST (sea surface temps for the newcomers) changes vastly change the character of a hurricane and how wind speed is determined to categorize hurricanes.  He said that with a temp change of as little as 0.8 degrees totally supercharges tropical depressions in this part of the world.  Apparently when allotting a CAT number for hurricanes (and cyclones for that matter) they measure them per their m/s wind speeds as they are monitored, so for pure example sake if a CAT2-3 is .  These systems are given their CAT number when the m/s speeds reach 5m/s increments.  We all looked a bit puzzled as why don't the hurricane would not be a higher CAT if it jumped a couple of m/s degrees but he said that we can only monitor wind speeds in 5 m/s blocks, and not single digits, so the authorities use 5 step blocks and then determine a CAT number.

One startling graphic showed how global warming and the SSTs have impacted on hurricane and cyclonic conditions over the last 10 years.  The spike in CAT5 hurricanes was mind blowing.  Whilst the trend was for general CAT2-3 storms, since Katrina just about all the hurricanes in the Atlantic have been CAT5s - something that NOAA just could not have imagined.  It has finally turned a light bulb on to weather forecasters and the like that even with an SST increase of just 0.8 degrees gives a hurricane more than 90% chance of reaching CAT5.

As far as wind speeds are concerned:  A rise of only 3-8% of m/s jumps the frequency of hurricane development in the Atlantic and Northern Australia a rise of thus:  CAT1-2 - 10%, CAT 2-3 50% CAT4-5 100%.  It changes number of overall hurricanes that would form. The 100% for CAT4-5 is relative to a 3% rise, this is what happened last year in the Atlantic basin.  Almost all of the hurricanes had little trouble to reach the highest CAT rating.    So if 1 m/s = 6.3 mph it does not take much to give a different CAT rating in their 5 m/s increments.

His work included assessing these big hurricanes and with regards to building codes in the US - a shocking indictment on the past government.  New Orleans - little known building codes, Florida - has codes but not regulated, Texas, no building codes whatsoever.  He said Australia has by far the best building codes on the planet.  Whilst there was some argument re tropical regions and what winds speed they were supposed to actually sustain, he said that 250km/h was the norm.   Unnervingly he said that if Darwin had taken a direct hit by Monica a couple of years ago - and any CAT5 now for the matter - you can kiss Darwin off the map again.  He said the amount of vegetation that blankets the city and suburbs is like a time bomb - he was blown away by what he saw as he has not been back to Darwin for many years.  Debris is the number one factor in CAT5 damage - he said that Tracy, Katrina and Andrew were 'man-made disasters' not natural.  People that continue to live and build in cyclone prone areas do so at their own risk, akin to our new suburb here which is right smack bang in the storm surge region - governments and developers should never allow dwellings to be built in these risk areas.  Prof Holland remarked that people can shelter from wind, but no-body can escape storm surge.  In Pakistan one area was 28cm below sea level and that surge killed almost 1 million people.

As far as the Australian region was concerned, much the same scenario re all of the above.  Higher SSTs and the importance of monsoonal troughs was touched upon.  He said whilst monsoonal troughs were to be monitored closely, cyclones such as Ingrid and Monica actually formed between land and ocean and still increased to CAT4-5, so the question of such strong storms not completely attached to a monsoon should be closely taken notice of.  Building high rise on cyclone prone coastal regions did not pose any real threat as far as he was concerned, they are built to high standards and he said considering what he went through with Tracy he would had rather been inside a high rise given a choice!  But building low rise in storm surge areas was his big argument.

Prof Holland also emphasized the importance of this country having recon aircraft to fly through cyclones much like the US.  Without airborne dtaa is is extremely difficult and frustrating for the BoM to accurately get information on our cyclones.  Satellites have obviously improved with software,but he said airborne data real time is vital.  He invented the aerosonde and this government rejected the idea and ironically the defence department bought it and uses it for military purposes - so much for the government having it's population's safety in mind eh?  The US recon fleet should be something the Australian government should adopt but manpower and money seems to be used and spent in other useless propositions it appears. 

So as far as these big storms being a bellweather - for sure, they are showing us that global change does indeed have an affect on the globes weather.  CAT5 hurricanes were almost non existent in relative frequency in early years, now they are all too common and increasing with every season.

A very informative night and wish he could have talked longer.  It gave me some valuable information and some of the stats were just incredible.  I'll try and get some data from his actual talk from BoM here has they have a copy of his presentation on their memory sticks I noticed!

Hope this was of interest people...did not take notes so had to think on the fly and have included Prof Holland's homepage for members ->

Title: Re: Professor Greg Holland /Hurricanes
Post by: Colin Maitland on 04 February 2009, 09:10:11 AM
That is brilliant information, I agree that Australia has good building codes for cyclones in QLD,WA and NT. we used to build to what we called W33 - w41 in Brisbane. That is to withstain winds of 33M/s  & 41m/s. The cyclone rating used to be North of King Street Caboolture, but that was later moved way further north.

 Further north  there was W 50 and W60. The ratings now have new names.  But in all honesty there are many flaws in the code, much of the testing was under,what you could say lab conditions, not taking in the variables, but has he said, you have flying debris being a major player in carnage along with low lying areas for tidal surge, and many other things to contend with. I dont think we would have much left if a full CAT 5 hit us directly.

As you said cyclone will intensify as this climate change continues, but it is too late for some of the dwellings already built and where authorities have allowed them to be built.

I have the privilege to build some commercial halls in NSW, and the crews from QLD were shocked at the tie down system , or lack of it.

So how do we use the information you have brought to our attention to educate the public. The building code has to improve a great deal. Darwin incorporated a storm shelter system into the laundry with there designs after cyclone Tracy.

I had a mate who lived in Cairns and used to have  cyclone parties, what they were unaware of, is that the army flew in forty thousand body bags for one of the storms ( I think it was 1992, there was a cyclone 5 times bigger than TC Tracey) that fortunately did not make land fall. I noticed on the news, in Cardwell this week they showed the locals having a party at the pub. The owner said " it was a way they coped with the situation."

Thanks for sharing that information with us, I found it educational, interesting and important.

Title: Re: Professor Greg Holland /Hurricanes
Post by: Mike on 04 February 2009, 10:26:32 AM
Just to add to that since your reply ignited something the professor said on building New Orleans and other cities where those big hurricanes hit some dwellings, there have massive concrete blocks in the roofs to 'stop the houses being uplifted' - when he viewed the destruction he asked one simple question:  Why are they not anchored to the ground?  They did not understand what he meant - he explained that imagine you're inside your home with this huge block of cement in the roof that is supposed to stop your house being lifted, then the hurricane hits and blows apart whatever supports it from underneath.  They got the picture!  No wonder some of those homes collapsed when the owners thought they'd be safe, if the hurricane did not kill you the cement block certainly would and even they were swept away by storm surge causing even more damage!

Even today typically here in Darwin our houses are all anchored some way either by U bolts anchoring the beans to the concrete pillars (elevated homes) and the ground level homes have Reo bars embedded into alternate columns of concrete into the core filled blocks.  even the corrugated iron we have has special clasps that seat under the screw heads that give some level of 'expansion' for the iron to move with the wind.  Whether in fact they will survive a constant battering of a CAT4-5 cyclone who knows, whatever their rated to nothing is 'set in concrete' until the event happens. photo he showed was the levy as Katrina struck.  The photo actually looked like a dam wall that was overflowing and in the foreground was a six foot tree.  The wall of water flowing from over the levy from the storm surge heading toward low lying suburbia was - unbelievable - 28 feet.  it was truly shocking to see this image and nothing was going to survive such a surge.