So Let’s Talk About the Science of How Climate Change Kicked Harvey into Higher Gear

Harvey is finally on the move.

After making a second landfall early Wednesday, the storm is passing slowly out of the East Texas region that has suffered so much first from Harvey’s initial lashing as a rapidly intensifying category 4 storm, and second from its long-lasting and unprecedented rainfall.

(Harvey rapidly intensifies into a category 4 monster just prior to landfall. This rapid intensification and other climate change related factors helped to make Harvey a more dangerous storm. Image source: NASA.)

At this point we can take a bit of a step back to look at the larger situation. Sure, impacts will probably continue and even worsen for some areas. And due to a historic pulse of water heading downstream, the hammered city of Houston is far from out of the woods.

But as with Sandy and so many other freakish strong storms in a present climate that has warmed by around 1.2 C above pre-industrial values, we would be remiss if we didn’t discuss the climate change related factors that gave Harvey more fuel, that helped it to rapidly intensify, that worsened its flooding — both from rains and from storm surge, and that may have helped to produce a still pocket in the upper level winds that allowed it to stick around for so long.

Warmer Ocean Surfaces Mean More Rapidly Intensifying Storms, Higher Peak Intensity of Worst Storms

Hurricanes like Harvey cannot readily form in cool waters below a range between 70 and 75 degrees Fahrenheit. Ideally, the storms require ocean surface temperatures warmer than 80 degrees (F). And the more heat that’s available at the ocean surface, the more energy that’s available for a storm when it does form.

This energy comes in the form of atmospheric lift. In other words, air rises off the water more vigorously as water temperature rises. This lifting energy is called convection. And the more that’s available, the more powerful storms can ultimately become.

(Sea surface temperatures were between 1 and 2 degrees Celsius above average as Harvey approached Texas. Human-forced climate change is causing the oceans to warm. This, in turn, provides more fuel for hurricanes like Harvey — helping them to rapidly intensify and pushing their peak strength higher. Image source: NOAA.)

According to Dr Michael Mann, Ocean surfaces in the Gulf of Mexico are fully 1 to 1.5 degrees Celsius warmer, on average, than they were just 30 years ago. This warming provides more energy for storms that do form. And this, in turn, raises the top potential intensity of storms.

Some scientists, like Dr. James Hansen, refer to this prevalence of worsening extremity as loading the climate dice. If, in the past, we were rolling with a die six with a 1 representing the lowest storm intensity and a 6 representing the highest, we’re now rolling with something like a die six +1. The result is that the strongest storms are stronger and the absolutely strongest storms have an ability to achieve previously unattainable strengths due to the fact that there’s a lot more energy there to kick them into a higher state.

Increased potential peak storm intensity as a climate change factor does not necessarily result in more tropical storms forming overall. That part of the science on hurricanes is highly uncertain. But that heat engine in the form of warmer surface waters is available for the storms that do form to tap. And that can make them a lot stronger and more damaging than they otherwise would have been.

(Loading the climate dice — changes in frequency of cold and warm temperatures also has an impact on heatwaves, droughts, wildfires, storm intensity, and heavy precipitation events. Image source: NASA.)

As Harvey approached land, it tapped the energy of this much warmer than normal ocean surface. And that energy caused the storm to rapidly strengthen — first from a minimal tropical storm to a Hurricane, and then from a minimal hurricane to a Category 4 monster. Meteorologists tend to call such periods of rapid intensification — bombification. This term comes from minimum pressures that rapidly drop in swiftly strengthening storms — seeming to bomb out. And due to warming, the science indicates that rapid strengthening is also more likely. With some models pointing toward a 10-20 fold increase in the frequency of rapidly intensifying storms by the end of this Century if human forced warming of ocean surfaces continues.

Warmer Atmosphere Means Heavier Rainfall

Related to a warming of the ocean surface (and land surfaces as well) is the basic scientific fact that such warming causes the amount of water vapor in the atmosphere to increase. In total, with each 1 degree Celsius of warming near the Earth’s surface, the atmosphere ends up holding about 6-7 percent more moisture. The properties of this warming-driven increase in atmospheric moisture are described by the scientifically proven Clausius–Clapeyron relation which defines, in meteorology, how atmospheric water vapor content is driven by various factors, including temperature.

If we dig just a little bit further into our understanding of how this scientific driver impacts the atmosphere in a warmer world, we find that not only does the moisture content of a warmer atmosphere increase, but both the rates of evaporation and precipitation increase.

 

(Global warming has brought with it a sharp increase in the number of record-breaking daily rainfall events. This is due to the fact that a warmer world holds more storm-fueling moisture in its atmosphere. This warmer, wetter atmosphere increased the peak potential rainfall from Harvey enabling it to smash records for rainfall rates and precipitation totals. Image source: Increased Record-Breaking Precipitation Events Under Global Warming.)

It is here that we return to the loaded climate dice mentioned above. If, as we find today, the Earth is about 1.2 degrees Celsius warmer than in the past, then the atmosphere holds more moisture. About 7-8 percent more. And since there’s more heat, evaporation is more intense where it does happen. This loads the climate dice for more intense droughts. But since what goes up in the form of evaporation results in a heavier load of moisture in the higher clouds and in the storms that do form, the rains that follow will also tend to be more intense. This loads the dice for more severe rainfall events. And we have a very clear scientific observation that the most extreme rainstorms are becoming much more intense overall (see above graphic).

For Harvey, this meant that more moisture was available to provide the record-setting rainfall amounts coming from that system. Peak rainfall totals from the storm are now at nearly 52 inches. This is the most rainfall ever to occur in Texas from a tropical system in our records. A measure that may also break the all-time U.S. record for rainfall from a tropical storm. And Harvey was enabled to produce such high rainfall amounts by a warmer atmosphere.

Harvey a Brown Ocean Cyclone?

Increasing rates of evaporation and precipitation had one obvious effect in Harvey — they increased the potential severity of rains coming from this kind of storm. But they also increase the ability of storms like Harvey to maintain strength or even intensify over land. If, for example, a storm like Harvey dumps a very heavy load of rainfall over land and if the evaporation from these recent rains has increased in a warming world, then storms like Harvey can tend to draw strength back from what amounts to a small ocean on land.

A recent NASA scientific paper on this issue describes a Brown Ocean effect. The 2013 NASA paper noted:

Before making landfall, tropical storms gather power from the warm waters of the ocean. Storms in the newly defined category derive their energy instead from the evaporation of abundant soil moisture – a phenomenon that Andersen and Shepherd call the “brown ocean.”

…The research also points to possible implications for storms’ response to climate change. “As dry areas get drier and wet areas get wetter, are you priming the soil to get more frequent inland tropical cyclone intensification?” asked Shepherd.

In essence, cyclones are better able to maintain strength or even re-intensify over wet areas of land in a warmer world due to increasing levels of evaporation and it was Harvey’s ability to maintain tropical storm strength over land for up to three days that helped to enable it to keep dropping such heavy volumes of rain.

Higher Seas Mean Worse Storm Surge Flooding

A warmer climate also brings with it the melt of continental glaciers and the thermal expansion of ocean waters. As glaciers flood into the world’s oceans, they rise. And since fossil fuel burning began at the start of the industrial age this related warming of the Earth and melting of glaciers has caused the oceans around the world to rise by more than 20 centimeters globally.

(Global warming increases the base ocean level which, in turn, worsens storm surge flooding. Harvey’s storm surge came in on this higher ramp. Image source: Sea Level Rise Science.)

Such higher seas alone are causing some coastal settlements to flood even on sunny days. But when storms like Harvey come roaring ashore, they do so on a higher overall launching pad. And this produces a multiplier effect for storm surge damages. A multiplier that would not have been there if the world hadn’t warmed.

Polar Warming Contributes to Blocking Patterns That Make Weather Stick Around in One Place Longer

Another climate change related factor that contributed to Harvey’s danger was its persist hovering over the same region. Harvey would not have been as damaging for Texas and the Gulf if it hadn’t hung over East Texas for more than five days. But here, again, we find that climate change related factors appear to be contributing to the increased lingering of various extreme weather producing systems.

To understand how, we need to look at the upper level atmospheric circulation pattern that moves weather systems from place-to-place. In other words — the Jet Stream. Climate change influences the Jet Stream by generating more warming at the poles than near the Equator. This in turn, according to the research of scientists like Dr Jennifer Francis, changes atmospheric slope. Warmer poles, in other words, create a taller atmosphere at the poles relative to the Equator.

(A high amplitude ridge-trough pattern helped to create a stagnant upper air slot in which Harvey stalled. This voiding of upper level steering currents enabled Harvey’s persistence. Some scientists are pointing toward increasing prevalence of these kinds of high amplitude ridges and troughs related to polar warming warming which is an upshot of global warming. Image source: Earth Nullschool.)

Since atmospheric slope and temperature differences between the poles and Equator drive the speed of the Jet Stream, warmer poles cause the Jet Stream to slow down and meander. This generates big ridges and deep troughs. It also appears to assist the generation of large blocking high pressure systems. And all of these features can tend to cause weather patterns to get stuck.

This year, a persistent trough in the Eastern U.S. has generated a consistent stormy pattern and aided in the firing of powerful thunderstorms that produced record rains over places like Kansas City, Missouri. In the West, a persistent ridge has produced record heat and very extreme wildfires while aiding the formation of a very intense flash drought in Montana and the Dakotas. Harvey got stuck in a stagnant pocket between these two relatively fixed weather patterns. A climate change related feature that may have increased the duration of Harvey and facilitated its record rains falling over such a long period.

Other Factors — Interaction With The Eastern Trough

Finally, we can state that Harvey’s interaction with the very deep eastern trough also helped to fuel it. The trough provided a moisture and instability kick to Harvey as it moved over Texas — helping to wring out tropical moisture over the Lone Star State. And if we accept the fact that polar warming contributed to the depth of this eastern trough by slowing down the Jet Stream, then its interaction with Harvey was also a climate change related factor.

Qualifying This Discussion

What can be said with certainty is that climate change did not cause the hurricane. That hurricanes do happen in a normal climate. But this is the same same thing as saying that home runs happen in both middle school and major league baseball. It’s all baseball, but the factors from one to the other have qualitatively changed in an obvious fashion. The same thing happens to weather in a warming world. And it is due to the changes in these underlying factors that we can say without a doubt that climate change made Harvey worse.

What we can also say is that our certainty of all these various climate change related factors involved varies. For example, we can say with very high certainty that global warming is worsening rainfall extremes and that sea level rise is worsening storm surges. We can say with a good level of confidence that the peak intensity of the worst storms is also increasing and that bombification is more likely. And we can say with moderate confidence that climate change is altering atmospheric circulation patterns (an issue that is still under considerable debate).

But the varying degrees of certainty with regards to these aspects do not change basic facts. Your climate is your weather averaged over 30 years. And if the world warms, both your climate and your weather change.

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Harvey Intensifies Slightly Just Prior to Second Landfall

Tropical Storm Harvey, which has dumped more than 51 inches of rain over parts of Texas and flooded hundreds of thousands of homes, intensified this afternoon over the Gulf of Mexico as it continued to move to the North-Northeast.

(Visible satellite imagery of Tropical Storm Harvey late afternoon on August 29th shows the storm slightly re-intensifying before a second landfall with strong rain bands again threatening Houston. Image source: The National Hurricane Center.)

As of the 4 PM CDT advisory from the National Hurricane Center, Harvey’s minimum central pressure had dropped to 994 mb even as its maximum sustained winds increased to 50 mph. This made Harvey a still rather weak tropical storm is it continued to lash sections of Eastern Texas and Louisiana with winds and rains.

Now a 5-day long event since threatening the Texas Coast as a category 4 storm on Thursday, Harvey has produced the worst flooding in Texas state history. In Houston, dams designed to contain a 1,000 year flood are overflowing — increasing already catastrophic flooding throughout the beleaguered city.

(After a brief respite, Houston’s eastern suburbs are again seeing heavy rain from Harvey. Image source: National Weather Service.)

Very heavy rains have fallen over Houston since Saturday. But during the early afternoon hours rains had lightened over the city as the heaviest squalls shifted further east over Beaumont. Recent weather radar imagery from the National Weather Service, however, has shown more intense rain bands again back-filling over Eastern Houston in coordination with Harvey’s recent re-intensification.

Tonight, Harvey is expected to track inland before being pulled northward by a trough and finally leaving Southeastern Texas behind. But not before giving the region one last lashing over the next 12-24 hours or so while dumping another 6-12 inches of rain.

RELATED STATEMENTS AND INFORMATION:

Links:

The National Hurricane Center

National Weather Service

Worst Tropical Rainfall Event in Texas History

Worst Tropical Rainfall Event in Texas History Made More Deadly by Climate Change: Harvey Totals Now Top 49 Inches

We can’t say that Hurricane Harvey was caused by climate change. But it was certainly worsened by it. — Dr. Michael Mann

Harvey is already the worst rainstorm in U.S. history and it’s still raining.Meteorologist Eric Holthaus

******

It’s the fifth day of an unprecedented rain event that one of the world’s top scientists is saying was made worse by climate change. Flood totals as of earlier this morning topped a record-smashing 49 inches. Emergency management officials are saying that this is a 1,000 year flood event (and it could get worse). And the rains are still falling as levees in and around the city of Houston over-top or fail.

If peak rainfall was the whole of this story, then things wouldn’t be quite so bad for Houston and other Texas cities. But with this particularly severe storm it’s a combination of size, severity and duration that has produced such terrible floods. Harvey’s persistent stall has brought very severe rains to a large swath running all the way from southeast Texas in an arc through Mississippi. And a huge flood basin from Victoria to Austin to Lufkin to Lake Charles has now received between 8 and nearly 50 inches of rain as of early Tuesday.

Such a large swath has resulted in a more significant pulse of waters flooding into streams, lakes, and reservoirs. This depth of zonal flooding generates more water pile ups as flows move downstream. Resulting in higher peaks at rivers in places like Houston and putting more stress on water management infrastructure. An infrastructure that was designed to handle the 100 to 1,000 year floods of a gentler climate but not the so-called 1,000 year or worse floods of an atmosphere loaded up with a much greater portion of storm-fueling heat and moisture.

That this will be the worst flood in Texas history by a number of measures goes without question. That the flood was made worse by climate change is a scientific fact. That Texas is still getting pummeled by a tragic blow that is costing both lives and tens of billions of dollars in damages is a foregone conclusion.

At this point, the question we need to be asking ourselves is how can we prepare for more of these kinds of extreme rainfall events — which are surely coming. And how can we honestly work together to reduce both their future intensity and damage? How can we ultimately protect lives and property in a world we have made more dangerous by burning fossil fuels and dumping carbon into the atmosphere? And how quickly can we resolve ourselves to stop making the problem worse?

UPDATED (1)

RELATED STATEMENTS AND INFORMATION:

Links:

Hurricane Harvey Made More Deadly by Climate Change

National Weather Service Houston

The Capital Weather Gang

Harvey is Already the Worst Rainstorm in U.S. History and it’s Still Raining

Houston Levee Failures

 

Houston Levee Failures: Reports Indicate that Reservoirs are Being Strained Past the Spillover Point

DEVELOPING STORY:

News reports Monday night from Houston KTRK indicated that water levels at Addicks and Barker Reservoirs were continuing to rise sharply despite controlled releases starting at 1 AM on Monday. According to these reports, the reservoirs had received upwards of 25 inches of rainfall. The National Weather Service indicated that another 25 inches may be on the way in total. And despite the controlled release, reservoir levels were continuing to rise at a rate of 4 inches per hour.

(Addicks and Barker Reservoirs spill into Buffalo Bayou, which then flows into downtown Houston. Earlier today controlled releases were begun in an attempt to slow water rise in the reservoirs. This release is failing to prevent rapid water rise within and around these reservoirs. Movement of flood waters into the reservoirs is pushing waters into subdivisions near the reservoirs even as risk of levee failure is rising. Image source: Harris County Flood Control District and Weather Underground.)

Such unprecedented rainfall totals caused city officials to warn that: “This event has the potential to exceed a 1,000 year flood plain threshold.” It’s worth noting that the Levees in Fort Bend County were designed only to manage a 100 year flood event and that the expected 59 foot crest of the Brazos River represented an 800 year flood event.

But by evening, very heavy thunderstorms were running in to Houston across Galveston Bay. These storms again pummeled the city with extraordinary rainfall amounts — pushing flood thresholds still higher.

As a result, concern about the communities surrounding these reservoirs is hitting a fever pitch. Flooding is now expected in all of the 41 city subdivisions surrounding Barker and also in all of the 52 subdivisions surrounding Addicks. In addition, three other neighborhoods could see flooding if water flanks the Addicks spillway.

More concerning, however, is this statement from KTRK:

In addition to these neighborhoods, officials have called for a mandatory evacuation of Inverness Forest on Cypress Creek and Northwood Pines on Spring Creek as a result of potential levee failures.

Throughout the day, there have been numerous indications that these reservoirs were under serious stress as more and more water rushed downstream. As of late afternoon, water levels had risen to 105 feet in the Addicks reservoir. And observers of various levees at the time had already noted that water was near overtopping in some places. This tweet from Jeff Linder shows water very close to the top of the Inverness Levee.

By evening, Addicks had topped 106 feet and Barker was at 101 feet with the water still rapidly rising. Meanwhile, a dam upstream in Brazos County burst at 9 PM — further adding to the torrent heading toward Houston. With imminent danger of worse floods approaching, the National Weather Service subsequently issued a very clear warning that residents in the impacted neighborhoods should evacuate before 11 PM (CDT) or risk being stranded. Such a clear warning was an indication that disaster officials expected a high risk that at least some of the impacted levees would be breached or spill over.

Uncontrolled Releases and Failures Begin Tuesday Morning

By Tuesday morning, reports were coming in that the Addicks reservoir had topped 108 feet and that parts of the dam section of that reservoir near Buffalo Bayou was flowing out through the emergency spillway. This spillover is adding more water to Buffalo Bayou — a main river running through Houston and a significant source of flooding thus far. The Addicks Dam, as of 11 AM CDT remained structurally sound and the main issue with the levee at that time was due to uncontrolled spill out through the emergency spillway. As of early Tuesday, officials expected levels at Addicks Dam to peak at more than 110 feet this week. Risk of dam breakage at this time, according to officials, is said to remain low.

Officials, as of late Tuesday morning, were increasingly concerned about a Barker Dam overflow due to rising waters in the Barker reservoir as well. Water gauges at Barker had been put out of commission by the rising waters as of last night. So it is difficult to clarify the situation at the Barker Dam at this time. However, Barker is expected to exceed the 101 foot level in which uncontrolled overflow occurs, ultimately peaking at 104 feet. As with Addick, Barker Dam presently remains structurally sound with no major risk of imminent breakage, according to officials.

Meanwhile, a levee failure has been reported Tuesday morning in Brazoria County, south of Houston, at Columbia Lakes. Emergency officials in the area were very concerned about residents sheltering in their homes in this region — urging all Columbia Lakes residents to “get out!”

(UPDATED — UPDATES TO FOLLOW)

RELATED REPORTS AND INFORMATION:

Links:

Addicks Dam Begins Overflowing

KTRK

KBXT

Harris County Flood Control District

Weather Underground

Hat tip to wili

Hat tip to eleggua

Hat tip to Andy in San Diego

With up to 42 Inches of Rain Already Dumped on Texas, Harvey’s Track Over Gulf Means 10-21 More to Come

By mid-afternoon Monday, a still very wet Harvey had back-tracked over the Gulf of Mexico. The storm has now dumped unprecedented, record-setting rains totaling more than 30 inches over a Houston that is being forced to release dam water into already flooded regions in order to prevent over-topping or worse. Meanwhile, nearby Dayton, as of this morning, had received nearly 40 inches since the storm began on Friday. And as of noon, Baytown, TX has seen 41.77 inches over the sixty hour storm period.

Harvey’s circulation is now located along the coast south and west of Galveston and it is edging slowly back over the Gulf of Mexico. The storm is still drawing copious volumes of moisture up from the Gulf. This moisture flood is still fueling a massive shield of rain and thunderstorms stretching over much of Eastern Texas, a good portion of Louisiana and parts of Mississippi. And with its center now moving back over water, this moisture flow and its related thunderstorms are again starting to intensify.

 

(Harvey’s rains shield reinvigorates as the storm once again crosses into the Gulf. Image source: The National Weather Service.)

Presently, the most intense rains from the system are clustered over Houston (still), adjacent portions of the Texas Coast, and Eastern Louisiana.

As of 4 PM CDT, Harvey had re-intensified somewhat to 997 mb with maximum sustained winds near 45 miles per hour. Over the next 24 hours, Harvey is expected to back slowly southward over the Gulf of Mexico, then turn back northward. By late Tuesday, the tropical storm is again expected to be closing in on the Texas Coast for a likely second landfall late Tuesday or early Wednesday.

Present satellite imagery shows Harvey reintensifying somewhat in the infrared — with stronger storms firing near Harvey’s Center and just to the north in the Houston region. A dry slot of air in the storm, however, is likely to limit re-strengthening as the storm passes over water during the next 12-24 hours.

(Harvey appears to restrengthen somewhat in the infrared satellite as it taps Gulf heat and moisture. Image source: The National Hurricane Center.)

As such, Harvey at present is still a rather dangerous rain event. An event that is now re-gathering some of its strength and intensity as it digs more deeply into Gulf moisture.

Earlier today, meteorologists noted an optimistic wedge of dry air moving into the system from Central Texas. Such a wedge would tend to tamp down rainfall rates over Houston and East Texas. And the region did get a bit of a respite from heavy rains earlier in the day. However, with the moisture tap to that abnormally warm Gulf now re-established, heavier rains are again filling in near the storm center and just to the north.

(NOAA is still showing a potential for in excess of 20 inches of rain in the Houston region even following the massive, historic deluge that has already been unleashed by a hurricane fueled by a record warm world. Image source: NOAA.)

As a result, Houston is likely to get socked with a third bout of very heavy rain tonight through tomorrow with a fourth bout likely on tap for late Tuesday night. And, presently, NOAA now predicts that up to another 21 inches of rain is on the way for the Houston region on top of the already historic totals of 20-40 inches that have inundated the city.

(UPDATED 7)

UPDATE (8): The latest advisory from the National Hurricane Center notes that:

Harvey is expected to produce additional rainfall accumulations of 10 to 20 inches through Thursday over parts of the upper Texas coast into southwestern Louisiana. Isolated storm totals may reach 50 inches over the upper Texas coast, including the Houston/Galveston metropolitan area. These rains are currently producing catastrophic and life-threatening flooding over large portions of southeastern Texas. DO NOT ATTEMPT TO TRAVEL IN THE AFFECTED AREA IF YOU ARE IN A SAFE PLACE. DO NOT DRIVE INTO FLOODED ROADWAYS. Please see warnings and products issued by your local National Weather Service office for additional information on this life-threatening situation.

This storm isn’t over folks. Not by a long shot.

RELATED INFORMATION AND STATEMENTS:

Links:

The National Weather Service

The National Hurricane Center

NOAA

Harvey Moves Back Over Water. Historic Rainfall Will Continue.

Hat tip to wili

Hat tip to eleggua

Harvey’s Flooding Already Catastrophic and Another 2-3 Feet of Rainfall is on the Way

For Houston, a city that hosts a massive oil industry, it’s the climate change related flood version of the Fort McMurray fire. And we may well be witnessing, at this time, a tragedy that we could have at least in part prevented, but didn’t.

*****

Last week at this time, meteorologists were tracking a tropical cyclone moving across the Caribbean. 5-7 day models indicated that the system would enter the Gulf of Mexico by late week. This Gulf was hotter than normal. And for the past three months it had been dumping an over-abundance of moisture into an unusually deep summer trough over the Eastern U.S. This interaction between two features related to human-forced climate change was already producing very severe thunderstorms that generated record rainfall over places like Kansas City, Missouri.

Harvey was very moisture rich. It issued from a tropical convergence zone and monsoon cycle that had hit unusually high intensity — due, at least in part, to abnormally warm ocean surface waters injecting much higher than normal moisture loads into the tropical atmosphere. And early last week there was some serious concern that intense tropical moisture in the form of Harvey could combine with a Gulf and Eastern U.S. weather and climate pattern that had already produced unprecedented rains to generate ultimately catastrophic results.

These fears have now been realized.

As of this afternoon,  parts of Houston and Southeast Texas had received more than 30 inches of rainfall — with up to 26 inches falling in just one 24-hour-period. Hourly rainfall rates at times have hit an equally unprecedented rate of up to six inches per hour. For context, one inch per hour rainfall rates in the past have been considered extreme. Six inches per hour is just off the charts. In many places, the most rain ever to fall over a one day time-frame was breached.

As we have seen so often around the world from globally increasing instances of record rainfall, roads flooded, cars were abandoned, and people were forced to climb onto their rooftops to flee the rising waters. In a Houston that is increasingly looking like post-Katrina New Orleans, more than 1,000 emergency calls for water rescues had been received by this morning. And with rivers hitting never-before-seen heights in a flood-prone city that is also facing the effect of rising sea levels, the rains were showing little sign of abating.

(Pivotal weather shows up to 32 inches of additional rainfall for the Houston region through Tuesday. The storm, however, may last through Thursday or later. Image source: Pivotal Weather.)

As much as 1-3 feet of additional rain is still expected from the storm. In the worst case, this would bring ultimate rainfall totals to 50-60+ inches. In a litany that we are hearing practically everywhere now — this would be the worst rainfall event Texas has ever seen in our records. It might, ultimately, be the worst flood from rainfall the U.S. has ever seen.

Moreover, weather models now indicate that Harvey may slowly track back toward the Gulf of Mexico. If this happens, a storm that is already pulling severe volumes of moisture in from the Gulf could be somewhat re-invigorated. Such a result would bring a second pulse of intense rains to parts of Southeast Texas and possibly Louisiana.

(September 1 GFS model shows remnants of Harvey interacting with a tropical cyclone south of Baja to continue to pull rains over Texas and Louisiana. Image source: Earth Nullschool.)

An additional concern is the fact that later this week Harvey shows a possible interaction with another stationary tropical cyclone forming near the southern tip of Baja in the Pacific. The two storms appear to interact to draw still more moisture from the abnormally warm Gulf over Southeast Texas later this week. Of course, this GFS-based forecast is still longer range — and therefore less certain. But the models do seem to continue to indicate a persistent heavy rainfall potential for an already catastrophically flooded region over an unprecedented long time frame.

This is exactly the kind of extreme rainfall event that some of us have feared coming from a warmer, more moisture-rich atmosphere in which weather systems have tended, more and more often, to persist and produce long-lasting effects. For the sake of all involved, we are now reduced to prayers and hopes that the worst case does not continue to be realized.

(UPDATED 9)

RELATED REPORTS AND STATEMENTS:

Links:

The National Weather Service

The National Hurricane Center

Harvey has Unloaded 9 Trillion Gallons of Water

Catastrophic Flooding Beyond Anything Experienced in Houston

Global Number of Record-Breaking Daily Rainfall Events

Harvey’s Approach Brings Potential Severe 5-Day Rainfall Event for Texas and Louisiana

Pivotal Weather

Earth Nullschool

Hat tip to Greg

Hat tip to eleggua

Not time to Let Our Guard Down With Harvey; Rainstorm Expected to Last 5-9 More Days

As of early afternoon on Saturday Harvey was about to be downgraded to a strong tropical storm after slamming into the Texas coast as a Category 4 monster hurricane packing 130 mph sustained winds. Residents along the coast are just now starting to assess the initial damage from this first major blow. However, the big rain event that is Harvey is just now getting started.

(Harvey’s rains expand over Eastern Texas at 245 PM EST. Image source: National Weather Service.)

According to the National Hurricane Center, the storm’s forward speed has now slowed down to about 2 miles per hour in a north-bound direction. Meanwhile, its shield of encircling rains is expanding to cover most of eastern Texas. These rains are very intense — producing accumulations of more than 1 inch per hour in many locations. And with Harvey stalling out, such heavy rains are expected to persist over basically the same region and at a similar high intensity for at least the next four days. After that time, Harvey is expected to persist and rains of lighter, but still flood-producing force, may continue to fall over parts of Texas for up to five more days.

(Harvey has already dumped nearly 15 inches of rain on some locations. Despite this fact, NOAA is still predicting more than 20 inches of additional rain. Some models are indicating that final totals could range from 40-60 inches in some locations after a 6-10 day rain event. Image source: NOAA.)

It’s worth noting that though up to 15 inches of rain have already fallen from Harvey, the longer range models still show in excess of another 20 inches coming from the storm over the next week. Many models indicate that more than 40 inches of rain could fall in total. And some of our best models yesterday indicated a potential for up to 60 inches in some locations by the time all is said and done.

In other words, this storm is far from over. The main event, in which Harvey may ultimately produce historic rainfall totals, is just getting ramped up. So now is not the time to relax our guard.

(UPDATED 1)

Links:

See Notes on Climate Change’s Influence on Harvey Here

The National Hurricane Center

National Weather Service

NOAA

Rainfall Rising Nearing 15 Inches in Some Locations

Global Forecast System Model Reanalysis

Harvey’s Mammoth Deluge Potential: Some Models Are Showing Storm Could Produce Five Feet of Rain

Media, Texas, and Gulf Coast residents take note: the thing to be most concerned about with regards to Harvey is not its admittedly life-threatening storm surge and strong winds, but what is shaping up to be a potentially historic rainfall event.

*****

The latest update from the National Hurricane Center shows that Harvey continues to strengthen and is now a category 4 storm. Packing 130 mph winds and a 941 mb minimum central pressure, the storm is certainly now very powerful. This new intensity is above the NHC’s previously expected peak strength for the storm just prior to landfall late tonight. The situation is thus becoming ever more dangerous.

But with Harvey, the serious concern we are facing is not just the usual and notably very dangerous high winds and storm surge flooding that go along with a category 4 storm. We are also looking at very severe and long lasting flooding rains that will have the potential to cause damage and disruption for not just months but for years to come.

A Devastating Rainfall Potential

(Southeast Texas has never seen 60 inches of rainfall from a tropical system. But that potential exists with Harvey.)

Consensus models now predict that peak rainfall totals will be around 35 inches in association with Harvey. This is due to the dual facts that Harvey is currently a very moisture-rich storm and that the storm is expected to stall for between 5 and 10 days following landfall. The storm is predicted to hover along the coastline, drawing in an unusually intense flow of moisture from a much warmer than normal Gulf, and to generate severe thunderstorms hour after hour, day after day. And this kind of rain event, if it emerges, could produce a disaster of historic proportions for Texas.

It’s worth noting that rainfall totals could also exceed the consensus forecast. Some models are now predicting upwards of 50 or 60 inches of rainfall by the time Harvey leaves the Texas area later next week (see top image above). The highest rainfall amounts ever produced by a tropical cyclone, in our records, for Texas is 48 inches. But there’s at least some possibility, with the perfect rainstorm that appears to be shaping up in Harvey, that these ultimate rainfall totals will be exceeded and a disaster of unprecedented proportions could emerge. But even if this worst-case doesn’t emerge, a 35 inch rainfall event would wreck untold destruction upon Texas’s southeastern cities.

Harvey strengthening as it moves toward shore

( Harvey rapidly strengthening to CAT 4 as it nears landfall. Image source: National Hurricane Center.)

Normally soft-spoken forecasters like Bob Henson and Eric Holthaus are not mincing words over the potential severity of the present situation. Last night, Bob Henson on twitter asked people: “Please don’t fixate on whether Harvey arrives as a Cat 2, 3, or 4. It’s the mammoth rainfall amounts (up to 35″) that will affect millions.” Meanwhile, Eric Holthaus warned: “This is scary. I have never seen a rainfall forecast like this in my entire career. Texas will be recovering from for years.”

Of course, we could dodge a bullet and rainfall totals could be lower for Harvey. It’s just that this event is currently trending toward a near worst case or worst case deluge-type storm that produces very heavy rains over the same region over nearly a week-long period.

Conditions in Context — This is Not Your Father’s Atmosphere

(The number of record rainfall events has increased dramatically during recent years. An observation attributed to human-forced climate change. Image source: Increased Record-Breaking Precipitation Events Under Global Warming.)

During recent years, a warmer than normal atmosphere has been producing more and more intense rain storms. The number of record daily rainfall instances around the world has been rising precipitously (see image above). This increasing severity is, in large part, due to the fact that human-forced warming amps up the hydrological cycle — producing more intense rain storms and more intense droughts. In other words, the climate dice are loaded for extreme rainfall and droughts in the present atmosphere. And it is in this atmosphere that Harvey has emerged. So we shouldn’t at all discount the fact that Harvey’s potential worst impacts from rainfall are now higher than they would have been even just a few decades ago. And this is one of the major reasons why we are seeing such a historic potential out of Harvey.

UPDATED (4)

UPDATE (5): As of 800 PM CDT the eye of Harvey crossed the coastline somewhere between Corpus Christi and Port O’Connor. Unfortunately, this storm is just getting started as a very severe one week long rain event is about to follow.

UPDATE (6): As of 1000 PM CDT and just following landfall, Harvey’s minimum central pressure had fallen to 938 mb. An indication that the storm was still strengthening as it began to cross the coastline. According to these reports (here and here), this is the 4th lowest barometric pressure recorded for a hurricane at landfall on the Texas coast since 1900. Maximum sustained winds remained at 130 mph with gusts to 160 mph.

Links:

National Hurricane Center

National Weather Service

Increased Record-Breaking Precipitation Events Under Global Warming

Greg Carbin

Eric Holthaus

Bob Henson

Hat tip to Greg

Hat tip to Titania

Hat tip to Wili

Hat tip to Andy in San Diego

Hat tip to Wharf Rat

Harvey’s Approach Brings Potential Severe 5-Day Rain Event For Texas and Louisiana

For the third time in less than one month, powerful thunderstorms have dropped torrential rains in excess of 6 inches over Kansas City, Missouri. In the most recent event, a frontal system dropping down over the U.S. midsection encountered a very heavy load of atmospheric moisture streaming in off a much warmer than normal Gulf of Mexico. The result for Kansas City was the production of a towering boomer that dropped 10 inches in just one night.

Such an intense downpour turned roads into rivers and forced numerous residents to take refuge on rooftops as the waters rose once again. By morning, more than 130 water rescues had been called in across the city.

(NOAA predicts heavy rainfall for Texas and Louisiana over the coming week. Image source: NOAA.)

But this particular extreme event may be a simple prelude for what’s to come as the remnants of Harvey sets its sights on the Texas and Louisiana Gulf Coasts. Harvey is expected to strengthen into a tropical storm or weak hurricane over a very warm and moist Gulf of Mexico within the next 48 hours. Models then predict that it will combine its substantial moisture load with that of the frontal system responsible for such severe flooding in Missouri last night.

Already NOAA is predicting some very significant rainfall amounts over the coming days for the Texas and Louisiana coastal regions (see image above). And Harvey represents a considerable rainfall potential given the fact that it is expected to stall over Texas and Louisiana for the better part of 5 days. With regards to NOAA rainfall predictions, it is worth noting that extreme local precipitation values have significantly exceeded NOAA predictions recently in the case of the most severe thunderstorms.

(2 PM EST assessment of Harvey’s path and potential for restrengthening. Image source: The National Hurricane Center.)

One possible spoiler for Harvey reforming is an upper level low swirling just southeast of Texas. This low could rip Harvey apart. But if this happens, that system would tend to also direct Harvey’s moisture toward Texas, Louisiana and Alabama. In which case, strong rainfall potentials are also likely. However, the National Hurricane Center expects this upper level low and associated squalls to move toward the north and west — generating rainy conditions for Texas and Louisiana ahead of Harvey and creating space for a more powerful and heavily moisture laden storm to form.

Lower than normal precipitation totals in the region of Coastal Texas during the past couple of months may help to alleviate flood potential if the rains from Harvey remain on the somewhat lighter side (2-4 inches) and if the system continues to be disorganized. A more organized system would tend to bring heavier precipitation totals. However, it is worth noting that during recent years, much warmer than normal sea surface temperatures have combined with a warmer atmosphere to spike heavy rainfall totals. A result of human-forced climate change due to ongoing rampant fossil fuel burning.

Links:

NOAA

The National Hurricane Center

Historic Flooding Leaves One Dead

Over 130 Calls Made to Kansas City Fire Department Amid Life Threatening Flooding Overnight

Hat tip to Wharf Rat

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