Harvey: Worst-Case Scenario Comes To Fruition

By Charlie Phillips AND Mark Ingalls

Tropical Storm Harvey has turned from a severe event into a catastrophic, record-breaking event that may go down as the costliest flooding disaster in the history of the United States. And yes, that includes Hurricane Katrina.

Some important notes before we start:

• If you are in Texas and find yourself in need of shelter, dial 211.
• If water has risen in your home, DO NOT go into your attic. If you can, climb onto your roof so airborne rescuers can spot you.
• Only call 911 when you are in need of life-saving assistance.
• Texas State Parks are offering free camping spaces to evacuees.
• If you are in on the roof in Houston, you can reach the Coast Guard at 281-464-4851, 281-464-4852, 281-464-4853, 281-464-4854, or 281-464-4855.

Last night, an extraordinarily heavy band of rain stalled directly over the Houston metro area, leaving massive flooding in its wake. Although rates have lessened, very heavy rain continues to fall over a wide swath of Southeastern Texas (including the Houston metro area) and Southwestern Louisiana, and it will increase in intensity overnight due to an increase in convection from the heat energy Harvey has absorbed throughout the day.

This is a comprehensive blog, and we will discuss past/current conditions, the forecast for the next week, and the poor model performance leading up to this event. Harvey was initially expected to make landfall as a strong tropical storm or weak hurricane, with heavy but not cataclysmic rainfall totals. The National Weather Service now says that the “breadth and intensity of this rainfall are beyond anything experienced before” and that “catastrophic flooding is expected to continue for days.”

Current Conditions

Rain/Flooding

As with any major weather system, rainfall amounts across Texas and Louisiana vary. Here are some of the highest values we’ve been able to find so far in Texas. Keep in mind that these were recorded at approximately 11 am CDT – current amounts are several inches higher.

Dayton – 27.45 inches
Dixie Farm Road, Brazoria County – 26.76 inches
Santa Fe – 24.50 inches
Pearland – 24.27 inches
First Colony – 23.84 inches
Baycliff – 23.78 inches

Rainfall across the Houston area has already exceeded record levels. Incredibly, there is so much more rain expected that the forecast rain totals on their own would approach or exceed records.

The animation below shows a radar loop of Harvey ending 11 am CDT today. Note the rapid development of the storm as it approached the coast and the extreme rainfall totals as it made landfall and stalled over Southeast Texas.

Full radar animation of #Harvey ending 11 am CDT Sun Aug 27th. Moisture continues to flow north/northwest from Gulf of Mexico into SE Texas. pic.twitter.com/siYkQI7Lz4

— NWS Eastern Region (@NWSEastern) August 27, 2017

Additionally, here’s a satellite loop of the past 7 days showing Harvey exploding from an open tropical wave into a Category 4 hurricane as it slowly moved over extremely warm water in the Gulf of Mexico. Credit goes to the University of Wisconsin-Madison Space Science and Engineering Center (SSEC)

Let’s talk flooding and road closures. Remember, if you see flood waters, turn around, don’t drown. We cannot emphasize enough the need to not drive through floodwaters. I was just watching a special report on ABC News showing a road that had been washed out. You have no way of knowing that a road hasn’t been completely destroyed below floodwaters.

I was going to attempt to provide a list of road closures, but there are just so many. Instead, here’s a map from TxDOT. You can access this map yourself on TxDOT’s website.

Just for funsies, here’s some TxDOT cameras from around Houston. There is so much flooding on Interstate 10 that many of the cameras are out of commission.

Of course, it’s not just the freeways that are flooding.

Buffalo Bayou in Houston. Unbelievable. #houwx #houstonflood #txwx #Harvey pic.twitter.com/grCKUmZYmr

— Mike Prendergast (@MPrendergastTX) August 27, 2017

Pretty much every waterbody of any substance is on the rise this afternoon. The Washington Post reported that over nine trillion gallons of water have fallen over the affected area thus far. One inch of rain over one acre of land weighs one ton. Figuring on the standard eight pounds per gallon of water, one inch of rain equates to 250 gallons of water on an acre of land. When we take that one acre and turn it into the thousands of square miles, and then take that one inch and apply the rainfall totals offered above, that’s a lot of water.

We could never show all of the flood gauges, but we’ll offer a few here. Record flooding is either occurring or expected.

Tornadoes:

Extreme rain is not the only threat to the region. The outer bands of Harvey have been packing several tornadoes, and a myriad of Tornado Watches and Warnings have been issued across Louisiana and Texas over the weekend.

The Storm Prediction Center has mapped out 13 tornado reports associated with Harvey on Saturday, 11 of those in Texas and the other three in Louisiana. Many of these tornadoes have caused damage, mostly just toppling trees in the saturated ground. Some tore off roofs and one is reported to have damaged four apartments in East Bernard, Texas.

As of 3:15 PM Central Time, there have been three tornado reports associated with Harvey today, one in Texas and two in Louisiana.

Pictured below is a shot from John Binns of a tornado that tore through Cypress on Saturday.

Wind:

Current sustained winds with Harvey are 40 mph, making it a weak tropical storm. That’s a far cry from the 130 mph sustained winds it had at landfall, but the fact that it is STILL a tropical storm after being over land since Friday night is a testament to how potent an energy source the nearby Gulf of Mexico is. Additionally, Harvey may also be getting some help from the “brown ocean effect,” which is where saturated soils and flooded areas from the storm’s rainfall provide the latent heat/moisture to sustain it.

Harvey made a direct hit at Rockport, and the damage there is nothing short of catastrophic. Roads to Rockport are largely impassable, and because cell phone service was interuppted, those in Rockport had no communication with the outside world.

Here are some pictures that show the extensive damage to Rockport. I retrieved these from the U.S. Customs and Border Control Flickr Page.

Here’s some drone footage from NBC showing the destruction in Rockport.

And finally, here’s a video from storm chaser Jeff Piotrowski in the eye wall of Harvey on Friday night.

The Forecast

Unfortunately, Harvey will continue to remain nearly stationary and will continue to direct extraordinarily heavy rain into Southeastern Texas and Southern Louisiana through Wednesday. And even after it weakens into a depression and slowly moves northward, moist southerly flow off the Gulf of Mexico will result in heavy rain over the area through next weekend and into early next week. I cannot stress enough how cataclysmic this storm will be for southeastern Texas. There was only one other time in my life when I was this mortified by a storm, and that was Hurricane Katrina.

Unbelievably, Harvey is actually expected to strengthen over the next several days as it meanders closer to the Gulf of Mexico and thus closer to 80+ degree water, which is the energy source for tropical cyclones. Harvey may also be getting some help from the “brown ocean effect,” which is where saturated soils and flooded areas from the storm’s rainfall provide the heat/moisture to sustain it. This same effect happened with Tropical Storm Allison, which caused catastrophic flooding in the Houston area in 2001. Harvey’s rainfall totals have already matched those of Allison, and multiple feet have yet to come. Credit to Tropical Tidbits (Levi Cowan) for the chart below.

Parts of southeastern Texas are predicted to pick up an additional 1-2 feet of rain through Tuesday morning, and could see another 2 feet from Tuesday through next weekend. I am confident that some places will have 60 inches of rainfall from this system by the time everything is said and done, and Houston could be one of those areas. Again, credit to Levi Cowan for the chart below.

Poor Model Performance Ahead Of The Storm

As recently as Tuesday, August 22nd, Harvey was expected to become no stronger than a tropical storm as it entered favorable conditions for development over the Gulf of Mexico, and while it was expected to stall over southeastern Texas, early forecasts had it moving out of the area by late Sunday, albeit slowly. Rainfall totals, while extremely impressive, were not expected to be catastrophic, with the hardest-hit places experiencing 8-16 inches of rain.

But over the next several days, it became apparent that Harvey would be far stronger than originally thought as it stalled over a deep path of warm water in the Gulf of Mexico. Moreover, it was predicted to stall over southeastern Texas for an even more extended period of time, leading to extreme rainfall totals there.

To summarize, intensity forecasts were poor with this storm, and the potential for truly catastrophic rainfall only became apparent a day or two before landfall. And current rainfall totals have already exceed the “catastrophic” scenarios painted by the models.

And this brings up an important point – while track forecasts have improved significantly over the past 30 years, hurricane intensity forecasts have seen much less improvement. In fact, despite the massive improvements in computing power and the huge amount of information available to us via satellites, short-term intensity forecasts are essentially the same now as they were in 1989, which is when we first started keeping verification records of intensity.

The reason for this discrepancy is because hurricane tracks are determined by synoptic (large-scale) features, such as the position/strength of ridges/troughs and their corresponding influence on upper-level winds. On the other hand, the processes that lead to changes in intensity are poorly understood and occur on a much smaller scale, and they cannot adequately be modeled with current model resolution.

I do think that the poor forecasts for this storm – and the corresponding poor preparation ahead of it – underscores the need for a significant investment to improve numerical weather prediction. For now, please donate to the American Red Cross if you are able. Those in the path of this historic storm need all the help they can get.

Charlie contributed to this report from Portland, Oregon.

Mark contributed to this report from St. Anthony, Idaho.