Wednesday, September 28, 2005
Aggie Preparation for Hurricane Rita
Texas A&M bookstore located on the "Aggie" north side of campus.
Sunday, September 25, 2005
What's up with them buoys?
I've spent a lot of time over the past couple days watching the buoys and tide gauges along the Texas and Louisiana coast to get an idea of what our project sites would be experiencing during Hurricane Rita. Unfortunately, my buoy watching experience was seriously disappointing - either something is wrong with them or my idiotic conspiracy is true!
As a brief explanation, the Saffir-Simpson hurricane classification is as follows (note: wind speed refers to sustained wind speed):
Based on a review of the NOAA data stations (1. NOAA Tides Online, 2. National Data Buoy Center, 3. National Hurricane Center), the highest wind speeds (gust - not sustained wind) recorded at the land station near Sabine Pass was 99mph with a maximum sustained wind speed of 82mph (2). The offshore buoy (42001) that had the lowest air pressure (close to 27in - which suggests the Hurricane passed directly over it) was even more disappointing with a measured wave height less than 35 ft and wind speeds near 50mph (reported during the storm) (2). While these two values correspond (to each other) based on wind/wave analysis (calculations that predicted the fully developed wave height based on a sustained wind speed) - they differ drastically when compared to the wind speeds reported by the National Weather Service and what the expected wind speed should have been based on the Saffir-Simpson Scale. I obtained a final final plot from buoy 42001 which shows (I'm guessing) information not posted in the Hurricane Rita update windows that shows the maximum wind speed near 90mph (created after the storm) (2).
Even the storm surge was less than that predicted for a stronger storm, ranging between 2-5ft along the LA and TX coasts (1).
While not a big deal to the general public, this discrepancy is cause for concern among coastal and ocean engineers as buoys and near shore data stations are the source of historical wind conditions that are used to create statistics that give us an idea what the probability is for a storm to occur during a projects lifetime. Not having correct wind conditions could distort the statistics and result in analysis that underpredicts the wind speeds for a particular area and projects that are under designed.
And, while I'm glad Rita didn't come ashore as a stronger storm, I'm disappointed that the tide gauges, buoys and other stations did not record better data - blah!, I wanted to watch it come ashore numerically!
Of course, for those interested in an alternative explanation Bob and I (because we obviously have nothing better to do) created a great theory that would explain why the buoys didn't record higher winds, waves or surges - and true to form it involves a government conspiracy...
As a brief explanation, the Saffir-Simpson hurricane classification is as follows (note: wind speed refers to sustained wind speed):
Based on a review of the NOAA data stations (1. NOAA Tides Online, 2. National Data Buoy Center, 3. National Hurricane Center), the highest wind speeds (gust - not sustained wind) recorded at the land station near Sabine Pass was 99mph with a maximum sustained wind speed of 82mph (2). The offshore buoy (42001) that had the lowest air pressure (close to 27in - which suggests the Hurricane passed directly over it) was even more disappointing with a measured wave height less than 35 ft and wind speeds near 50mph (reported during the storm) (2). While these two values correspond (to each other) based on wind/wave analysis (calculations that predicted the fully developed wave height based on a sustained wind speed) - they differ drastically when compared to the wind speeds reported by the National Weather Service and what the expected wind speed should have been based on the Saffir-Simpson Scale. I obtained a final final plot from buoy 42001 which shows (I'm guessing) information not posted in the Hurricane Rita update windows that shows the maximum wind speed near 90mph (created after the storm) (2).
Even the storm surge was less than that predicted for a stronger storm, ranging between 2-5ft along the LA and TX coasts (1).
While not a big deal to the general public, this discrepancy is cause for concern among coastal and ocean engineers as buoys and near shore data stations are the source of historical wind conditions that are used to create statistics that give us an idea what the probability is for a storm to occur during a projects lifetime. Not having correct wind conditions could distort the statistics and result in analysis that underpredicts the wind speeds for a particular area and projects that are under designed.
And, while I'm glad Rita didn't come ashore as a stronger storm, I'm disappointed that the tide gauges, buoys and other stations did not record better data - blah!, I wanted to watch it come ashore numerically!
Of course, for those interested in an alternative explanation Bob and I (because we obviously have nothing better to do) created a great theory that would explain why the buoys didn't record higher winds, waves or surges - and true to form it involves a government conspiracy...
Saturday, September 03, 2005
Katrina, Andrew
For my sister, I've written a brief summary of the difference between Hurricane Andrew in 1992 and Hurricane Katrina in 2005.
As shown in Figure 1, Hurricane Andrew made landfall in south central Louisana while Hurricane Andrew made landfall just east of New Orleans, shown in Figure 2.
Figure 1: Path of Hurricane Andrew, 1992
Figure 2: Path of Hurricane Katrina, 2005
A close up of New Orleans, shows a better picture of what the differences are, shown in Figures 3.
Figure 3: New Orleans
The most notable difference between the two is the location where landfall was made. Hurricane Andrew storm passed to the west of New Orleans and would have reduced in strength prior to hitting New Orleans. To simplify the analysis of the 2 storms, I'll neglect this and assume that Andrew passed New Orleans at the same strength it made landfall at.
To further simplify the analysis, I will just refer to wind direction and setup. There are of course other factors that amplified the differences between the two storms, such as pressure, size of the hurricanes, the rivers/channels that flow through New Orleans, and then there's wave dyanmics, and other coastal processes, but wind provides the simpliest explanation.
Hurricanes rotate in a counter clockwise direction. For a storm that passes to the west of New Orleans, the wind direction would have been to the north and east. This is important because the wind would have pushed water away from New Orleans rather than directly at it. In addition to waves, the wind would create a buildup along the northern shore of Lake Pontchartrain, called setup. This is what happened during Hurricane Andrew.
Hurricanes that pass to the east of New Orleans would have had a wind direction to the west and south. This would have pushed water directly onto the levees protecting New Orleans, like Katrina did. The water build up would have run along the levee, down channels, sort of probbing for weak spots.
Now, from my sources through work, the levees were built to withstand a category 3 hurricane, and Katrina was on the upper tolerance of the levees design. Tack on that sections of the levee had sunken by four feet (much of LA is sinking and losing more than an acre of wetland every 30 minutes that protect LA from storms and the gulf, but that's a whole different story.
If you're interested I recommend reading Bayou Farewell by Mike Tidwell. I also have some other Coastal studies at work) and were not repaired due to budget cuts and other constraints, its easy to see how such a disaster occured.
As shown in Figure 1, Hurricane Andrew made landfall in south central Louisana while Hurricane Andrew made landfall just east of New Orleans, shown in Figure 2.
Figure 1: Path of Hurricane Andrew, 1992
Figure 2: Path of Hurricane Katrina, 2005
A close up of New Orleans, shows a better picture of what the differences are, shown in Figures 3.
Figure 3: New Orleans
The most notable difference between the two is the location where landfall was made. Hurricane Andrew storm passed to the west of New Orleans and would have reduced in strength prior to hitting New Orleans. To simplify the analysis of the 2 storms, I'll neglect this and assume that Andrew passed New Orleans at the same strength it made landfall at.
To further simplify the analysis, I will just refer to wind direction and setup. There are of course other factors that amplified the differences between the two storms, such as pressure, size of the hurricanes, the rivers/channels that flow through New Orleans, and then there's wave dyanmics, and other coastal processes, but wind provides the simpliest explanation.
Hurricanes rotate in a counter clockwise direction. For a storm that passes to the west of New Orleans, the wind direction would have been to the north and east. This is important because the wind would have pushed water away from New Orleans rather than directly at it. In addition to waves, the wind would create a buildup along the northern shore of Lake Pontchartrain, called setup. This is what happened during Hurricane Andrew.
Hurricanes that pass to the east of New Orleans would have had a wind direction to the west and south. This would have pushed water directly onto the levees protecting New Orleans, like Katrina did. The water build up would have run along the levee, down channels, sort of probbing for weak spots.
Now, from my sources through work, the levees were built to withstand a category 3 hurricane, and Katrina was on the upper tolerance of the levees design. Tack on that sections of the levee had sunken by four feet (much of LA is sinking and losing more than an acre of wetland every 30 minutes that protect LA from storms and the gulf, but that's a whole different story.
If you're interested I recommend reading Bayou Farewell by Mike Tidwell. I also have some other Coastal studies at work) and were not repaired due to budget cuts and other constraints, its easy to see how such a disaster occured.
Thursday, September 01, 2005
Post-Katrina Aerial Photos
NOAA posted images of the damage caused by Hurricane Katrina here.
I was looking through the aerials along Grand Isle, LA where we have a coastal shoreline stabilization project and saw written out of debris "HELP!" God help the poor soul trapped on Grand Isle, hopefully the Mayor made it out to the island with plenty of supplies yesterday. He had called to let us know that the roads were blocked and that he would be traveling out in a boat to survey the damage.
Out of curiousity, I took one of the photos and georeferenced it using a georeferenced aerial image from 2004 that we had at work. The rectification isn't perfect, but it's close enough to get an idea what happened. The aerial is of the southwest tip of Grand Isle, near Caminada Pass. The first picture was taken in 2004, the second after Hurricane Katrina.
2004 DOQ Aerial Image of the Southwest corner of Grand Isle
2005 Post-Katrina Aerial Image of the Southwest corner of Grand Isle
2005 Post Katrina image overlaid on top of 2004 DOQ
I was looking through the aerials along Grand Isle, LA where we have a coastal shoreline stabilization project and saw written out of debris "HELP!" God help the poor soul trapped on Grand Isle, hopefully the Mayor made it out to the island with plenty of supplies yesterday. He had called to let us know that the roads were blocked and that he would be traveling out in a boat to survey the damage.
Out of curiousity, I took one of the photos and georeferenced it using a georeferenced aerial image from 2004 that we had at work. The rectification isn't perfect, but it's close enough to get an idea what happened. The aerial is of the southwest tip of Grand Isle, near Caminada Pass. The first picture was taken in 2004, the second after Hurricane Katrina.
2004 DOQ Aerial Image of the Southwest corner of Grand Isle
2005 Post-Katrina Aerial Image of the Southwest corner of Grand Isle
2005 Post Katrina image overlaid on top of 2004 DOQ
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